{"collection":"aor","html_url":"https://unchartedknowledge.5gfusion.net/browse/aor/darwin/descent/dm08.htm","path":"aor/darwin/descent/dm08.htm","source_url":"https://sacred-texts.com/aor/darwin/descent/dm08.htm","text":"Part Two - Sexual Selection\nChapter VIII - Principles of Sexual Selection\n WITH animals which have their sexes separated, the males necessarily\ndiffer from the females in their organs of reproduction; and these are\nthe primary sexual characters. But the sexes often differ in what\nHunter has called secondary sexual characters, which are not\ndirectly connected with the act of reproduction; for instance, the\nmale possesses certain organs of sense or locomotion, of which the\nfemale is quite destitute, or has them more highly-developed, in order\nthat he may readily find or reach her; or again the male has special\norgans of prehension for holding her securely. These latter organs, of\ninfinitely diversified kinds, graduate into those which are commonly\nranked as primary, and in some cases can hardly be distinguished\nfrom them; we see instances of this in the complex appendages at the\napex of the abdomen in male insects. Unless indeed we confine the term\n\"primary\" to the reproductive glands, it is scarcely possible to\ndecide which ought to be called primary and which secondary.\n The female often differs from the male in having organs for the\nnourishment or protection of her young, such as the mammary glands\nof mammals, and the abdominal sacks of the marsupials. In some few\ncases also the male possesses similar organs, which are wanting in the\nfemale, such as the receptacles for the ova in certain male fishes,\nand those temporarily developed in certain male frogs. The females\nof most bees are provided with a special apparatus for collecting\nand carrying pollen, and their ovipositor is modified into a sting for\nthe defense of the larvae and the community. Many similar cases\ncould be given, but they do not here concern us. There are, however,\nother sexual differences quite unconnected with the primary\nreproductive organs, and it is with these that we are more\nespecially concerned such as the greater size, strength, and pugnacity\nof the male, his weapons of offence or means of defence against\nrivals, his gaudy colouring and various ornaments, his power of\nsong, and other such characters.\n Besides the primary and secondary sexual differences, such as the\nforegoing, the males and females of some animals differ in\nstructures related to different habits of life, and not at all, or\nonly indirectly, to the reproductive functions. Thus the females of\ncertain flies (Culicidae and Tabanidae) are blood-suckers, whilst\nthe males, living on flowers, have mouths destitute of mandibles.* The\nmales of certain moths and of some crustaceans (e. g. Tanais) have\nimperfect, closed mouths, and cannot feed. The complemental males of\ncertain cirripedes live like epiphytic plants either on the female\nor the hermaphrodite form, and are destitute of a mouth and of\nprehensile limbs. In these cases it is the male which has been\nmodified, and has lost certain important organs, which the females\npossess. In other cases it is the female which has lost such parts;\nfor instance, the female glow-worm is destitute of wings, as also\nare many female moths, some of which never leave their cocoons. Many\nfemale parasitic crustaceans have lost their natatory legs. In some\nweevil-beetles (Curculionidae) there is a great difference between the\nmale and female in the length of the rostrum or snout;*(2) but the\nmeaning of this and of many analogous differences, is not at all\nunderstood. Differences of structure between the two sexes in relation\nto different habits of life are generally confined to the lower\nanimals; but with some few birds the beak of the male differs from\nthat of the female. In the Huia of New Zealand the difference is\nwonderfully great, and we hear from Dr. Buller*(3) that the male\nuses his strong beak in chiselling the larvae of insects out of\ndecayed wood, whilst the female probes the softer parts with her far\nlonger, much curved and pliant beak: and thus they mutually aid each\nother. In most cases, differences of structure between the sexes are\nmore or less directly connected with the propagation of the species:\nthus a female, which has to nourish a multitude of ova, requires\nmore food than the male, and consequently requires special means for\nprocuring it. A male animal, which lives for a very short time,\nmight lose its organs for procuring food through disuse, without\ndetriment; but he would retain his locomotive organs in a perfect\nstate, so that he might reach the female. The female, on the other\nhand, might safely lose her organs for flying, swimming, or walking,\nif she gradually acquired habits which rendered such powers useless.\n * Westwood, Modern Classification of Insects, vol. ii., 1840, p.\n541. For the statement about Tanais, mentioned below, I am indebted to\nFritz Muller.\n *(2) Kirby and Spence, Introduction to Entomology, vol. iii.,\n1826, p. 309.\n *(3) Birds of New Zealand, 1872, p. 66.\n We are, however, here concerned only with sexual selection. This\ndepends on the advantage which certain individuals have over others of\nthe same sex and species solely in respect of reproduction. When, as\nin the cases above mentioned, the two sexes differ in structure in\nrelation to different habits of life, they have no doubt been modified\nthrough natural selection, and by inheritance, limited to one and\nthe same sex. So again the primary sexual organs, and those for\nnourishing or protecting the young, come under the same influence; for\nthose individuals which generated or nourished their offspring best,\nwould leave, ceteris paribus, the greatest number to inherit their\nsuperiority; whilst those which generated or nourished their offspring\nbadly, would leave but few to inherit their weaker powers. As the male\nhas to find the female, he requires organs of sense and locomotion,\nbut if these organs are necessary for the other purposes of life, as\nis generally the case, they will have been developed through natural\nselection. When the male has found the female, he sometimes absolutely\nrequires prehensile organs to hold her; thus Dr. Wallace informs me\nthat the males of certain moths cannot unite with the females if their\ntarsi or feet are broken. The males of many oceanic crustaceans,\nwhen adult, have their legs and antennae modified in an\nextraordinary manner for the prehension of the female; hence we may\nsuspect that it is because these animals are washed about by the waves\nof the open sea, that they require these organs in order to\npropagate their kind, and if so, their development has been the result\nof ordinary or natural selection. Some animals extremely low in the\nscale have been modified for this same purpose; thus the males of\ncertain parasitic worms, when fully grown, have the lower surface of\nthe terminal part of their bodies roughened like a rasp, and with this\nthey coil round and permanently hold the females.*\n * M. Perrier advances this case (Revue Scientifique, Feb. 1, 1873,\np. 865) as one fatal to the belief in sexual election, inasmuch as\nhe supposes that I attribute all the differences between the sexes\nto sexual selection. This distinguished naturalist, therefore, like so\nmany other Frenchmen, has not taken the trouble to understand even the\nfirst principles of sexual selection. An English naturalist insists\nthat the claspers of certain male animals could not have been\ndeveloped through the choice of the female! Had I not met with this\nremark, I should not have thought it possible for any one to have read\nthis chapter and to have imagined that I maintain that the choice of\nthe female had anything to do with the development of the prehensile\norgans in the male.\n When the two sexes follow exactly the same habits of life, and the\nmale has the sensory or locomotive organs more highly developed than\nthose of the female, it may be that the perfection of these is\nindispensable to the male for finding the female; but in the vast\nmajority of cases, they serve only to give one male an advantage\nover another, for with sufficient time, the less well-endowed males\nwould succeed in pairing with the females; and judging from the\nstructure of the female, they would be in all other respects equally\nwell adapted for their ordinary habits of life. Since in such cases\nthe males have acquired their present structure, not from being better\nfitted to survive in the struggle for existence, but from having\ngained an advantage over other males, and from having transmitted this\nadvantage to their male offspring alone, sexual selection must here\nhave come into action. It was the importance of this distinction which\nled me to designate this form of selection as Sexual Selection. So\nagain, if the chief service rendered to the male by his prehensile\norgans is to prevent the escape of the female before the arrival of\nother males, or when assaulted by them, these organs will have been\nperfected through sexual selection, that is by the advantage\nacquired by certain individuals over their rivals. But in most cases\nof this kind it is impossible to distinguish between the effects of\nnatural and sexual selection. Whole chapters could be filled with\ndetails on the differences between the sexes in their sensory,\nlocomotive, and prehensile organs. As, however, these structures are\nnot more interesting than others adapted for the ordinary purposes\nof life, I shall pass them over almost entirely, giving only a few\ninstances under each class.\n There are many other structures and instincts which must have been\ndeveloped through sexual selection- such as the weapons of offence and\nthe means of defence- of the males for fighting with and driving\naway their rivals- their courage and pugnacity- their various\nornaments- their contrivances for producing vocal or instrumental\nmusic- and their glands for emitting odours, most of these latter\nstructures serving only to allure or excite the female. It is clear\nthat these characters are the result of sexual and not of ordinary\nselection, since unarmed, unornamented, or unattractive males would\nsucceed equally well in the battle for life and in leaving a\nnumerous progeny, but for the presence of better endowed males. We may\ninfer that this would be the case, because the females, which are\nunarmed and unornamented, are able to survive and procreate their\nkind. Secondary sexual characters of the kind just referred to, will\nbe fully discussed in the following chapters, as being in many\nrespects interesting, but especially as depending on the will, choice,\nand rivalry of the individuals of either sex. When we behold two males\nfighting for the possession of the female, or several male birds\ndisplaying their gorgeous plumage, and performing strange antics\nbefore an assembled body of females, we cannot doubt that, though\nled by instinct, they know what they are about, and consciously\nexert their mental and bodily powers.\n Just as man can improve the breeds of his game-cocks by the\nselection of those birds which are victorious in the cock-pit, so it\nappears that the strongest and most vigorous males, or those\nprovided with the best weapons, have prevailed under nature, and\nhave led to the improvement of the natural breed or species. A\nslight degree of variability leading to some advantage, however\nslight, in reiterated deadly contests would suffice for the work of\nsexual selection; and it is certain that secondary sexual characters\nare eminently variable. Just as man can give beauty, according to\nhis standard of taste, to his male poultry, or more strictly can\nmodify the beauty originally acquired by the parent species, can\ngive to the Sebright bantam a new and elegant plumage, an erect and\npeculiar carriage- so it appears that female birds in a state of\nnature, have by a long selection of the more attractive males, added\nto their beauty or other attractive qualities. No doubt this implies\npowers of discrimination and taste on the part of the female which\nwill at first appear extremely improbable; but by the facts to be\nadduced hereafter, I hope to be able to shew that the females actually\nhave these powers. When, however, it is said that the lower animals\nhave a sense of beauty, it must not be supposed that such sense is\ncomparable with that of a cultivated man, with his multiform and\ncomplex associated ideas. A more just comparison would be between\nthe taste for the beautiful in animals, and that in the lowest\nsavages, who admire and deck themselves with any brilliant,\nglittering, or curious object.\n From our ignorance on several points, the precise manner in which\nsexual selections acts is somewhat uncertain. Nevertheless if those\nnaturalists who already believe in the mutability of species, will\nread the following chapters, they will, I think, agree with me, that\nsexual selection has played an important part in the history of the\norganic world. It is certain that amongst almost all animals there\nis a struggle between the males for the possession of the female. This\nfact is so notorious that it would be superfluous to give instances.\nHence the females have the opportunity of selecting one out of several\nmales, on the supposition that their mental capacity suffices for\nthe exertion of a choice. In many cases special circumstances tend\nto make the struggle between the males particularly severe. Thus the\nmales of our migratory birds generally arrive at their places of\nbreeding before the females, so that many males are ready to contend\nfor each female. I am informed by Mr. Jenner Weir, that the\nbird-catchers assert that this is invariably the case with the\nnightingale and blackcap, and with respect to the latter he can\nhimself confirm the statement.\n Mr. Swaysland of Brighton has been in the habit, during the last\nforty years, of catching our migratory birds on their first arrival,\nand he has never known the females of any species to arrive before\ntheir males. During one spring he shot thirty-nine males of Ray's\nwagtail (Budytes raii) before he saw a single female. Mr. Gould has\nascertained by the dissection of those snipes which arrive the first\nin this country, that the males come before the females. And the\nlike holds good with most of the migratory birds of the United\nStates.* The majority of the male salmon in our rivers, on coming up\nfrom the sea, are ready to breed before the females. So it appears\nto be with frogs and toads. Throughout the great class of insects\nthe males almost always are the first to emerge from the pupal\nstate, so that they generally abound for a time before any females can\nbe seen.*(2) The cause of this difference between the males and\nfemales in their periods of arrival and maturity is sufficiently\nobvious. Those males which annually first migrated into any country,\nor which in the spring were first ready to breed, or were the most\neager, would leave the largest number of offspring; and these would\ntend to inherit similar instincts and constitutions. It must be\nborne in mind that it would have been impossible to change very\nmaterially the time of sexual maturity in the females, without at\nthe same time interfering with the period of the production of the\nyoung- a period which must be determined by the seasons of the year.\nOn the whole there can be no doubt that with almost all animals, in\nwhich the sexes are separate, there is a constantly recurrent struggle\nbetween the males for the possession of the females.\n * J. A. Allen, on the \"Mammals and Winter Birds of Florida,\"\nBulletin of Comparative Zoology, Harvard College, p. 268.\n *(2) Even with those plants in which the sexes are separate, the\nmale flowers are generally mature before the female. As first shewn by\nC. K. Sprengel, many hermaphrodite plants are dichogamous; that is,\ntheir male and female organs are not ready at the same time, so that\nthey cannot be self-fertilised. Now in such flowers, the pollen is\nin general matured before the stigma, though there are exceptional\ncases in which the female organs are before-hand.\n Our difficulty in regard to sexual selection lies in understanding\nhow it is that the males which conquer other males, or those which\nprove the most attractive to the females, leave a greater number of\noffspring to inherit their superiority than their beaten and less\nattractive rivals. Unless this result does follow, the characters\nwhich give to certain males an advantage over others, could not be\nperfected and augmented through sexual selection. When the sexes exist\nin exactly equal numbers, the worst-endowed males will (except where\npolygamy prevails), ultimately find females, and leave as many\noffspring, as well fitted for their general habits of life, as the\nbest-endowed males. From various facts and considerations, I\nformerly inferred that with most animals, in which secondary sexual\ncharacters are well developed, the males considerably exceeded the\nfemales in number; but this is not by any means always true. If the\nmales were to the females as two to one, or as three to two, or even\nin a somewhat lower ratio, the whole affair would be simple; for the\nbetter-armed or more attractive males would leave the largest number\nof offspring. But after investigating, as far as possible, the\nnumerical proportion of the sexes, I do not believe that any great\ninequality in number commonly exists. In most cases sexual selection\nappears to have been effective in the following manner.\n Let us take any species, a bird for instance, and divide the females\ninhabiting a district into two equal bodies, the one consisting of the\nmore vigorous and better-nourished individuals, and the other of the\nless vigorous and healthy. The former, there can be little doubt,\nwould be ready to breed in the spring before the others; and this is\nthe opinion of Mr. Jenner Weir, who has carefully attended to the\nhabits of birds during many years. There can also be no doubt that the\nmost vigorous, best-nourished and earliest breeders would on an\naverage succeed in rearing the largest number of fine offspring.*\nThe males, as we have seen, are generally ready to breed before the\nfemales; the strongest, and with some species the best armed of the\nmales, drive away the weaker; and the former would then unite with the\nmore vigorous and better-nourished females, because they are the first\nto breed.*(2) Such vigorous pairs would surely rear a larger number of\noffspring than the retarded females, which would be compelled to unite\nwith the conquered and less powerful males, supposing the sexes to\nbe numerically equal; and this is all that is wanted to add, in the\ncourse of successive generations, to the size, strength and courage of\nthe males, or to improve their weapons.\n * Here is excellent evidence on the character of the offspring\nfrom an experienced ornithologist. Mr. J. A. Allen, in speaking\n(Mammals and Winter Birds of E. Florida, p. 229) of the later\nbroods, after the accidental destruction of the first, says, that\nthese \"are found to be smaller and paler-coloured than those hatched\nearlier in the season. In cases where several broods are reared each\nyear, as a general rule the birds of the earlier broods seem in all\nrespects the most perfect and vigorous.\"\n *(2) Hermann Muller has come to this same conclusion with respect to\nthose female bees which are the first to emerge from the pupa each\nyear. See his remarkable essay, \"Anwendung der Darwin'schen Lehre\nauf Bienen,\" Verh. d. V. Jahrg., xxix., p. 45\n But in very many cases the males which conquer their rivals, do\nnot obtain possession of the females, independently of the choice of\nthe latter. The courtship of animals is by no means so simple and\nshort an affair as might be thought. The females are most excited\nby, or prefer pairing with, the more ornamented males, or those\nwhich are the best songsters, or play the best antics; but it is\nobviously probable that they would at the same time prefer the more\nvigorous and lively males, and this has in some cases been confirmed\nby actual observation.* Thus the more vigorous females, which are\nthe first to breed, will have the choice of many males; and though\nthey may not always select the strongest or best armed, they will\nselect those which are vigorous and well armed, and in other\nrespects the most attractive. Both sexes, therefore, of such early\npairs would as above explained, have an advantage over others in\nrearing offspring; and this apparently has sufficed during a long\ncourse of generations to add not only to the strength and fighting\npowers of the males, but likewise to their various ornaments or\nother attractions.\n * With respect to poultry, I have received information, hereafter to\nbe given, to this effect. Even birds, such as pigeons, which pair\nfor life, the female, as I hear from Mr. Jenner Weir, will desert\nher mate if he is injured or grows weak.\n In the converse and much rarer case of the males selecting\nparticular females, it is plain that those which were the most\nvigorous and had conquered others, would have the freest choice; and\nit is almost certain that they would select vigorous as well as\nattractive females. Such pairs would have an advantage in rearing\noffspring, more especially if the male had the power to defend the\nfemale during the pairing-season as occurs with some of the higher\nanimals, or aided her in providing for the young. The same\nprinciples would apply if each sex preferred and selected certain\nindividuals of the opposite sex; supposing that they selected not only\nthe more attractive, but likewise the more vigorous individuals.\n Numerical Proportion of the Two Sexes.- I have remarked that\nsexual selection would be a simple affair if the males were\nconsiderably more numerous than the females. Hence I was led to\ninvestigate, as far as I could, the proportions between the two\nsexes of as many animals as possible; but the materials are scanty.\nI will here give only a brief abstract of the results, retaining the\ndetails for a supplementary discussion, so as not to interfere with\nthe course of my argument. Domesticated animals alone afford the means\nof ascertaining the proportional numbers at birth; but no records have\nbeen specially kept for this purpose. By indirect means, however, I\nhave collected a considerable body of statisties, from which it\nappears that with most of our domestic animals the sexes are nearly\nequal at birth. Thus 25,560 births of race-horses have been recorded\nduring twenty-one years, and the male births were to the female births\nas 99.7 to 100. In greyhounds the inequality is greater than with\nany other animal, for out of 6878 births during twelve years, the male\nbirths were to the female as 110.1 to 100. It is, however, in some\ndegree doubtful whether it is safe to infer that the proportion\nwould be the same under natural conditions as under domestication; for\nslight and unknown differences in the conditions affect the proportion\nof the sexes. Thus with mankind, the male births in England are as\n104.5, in Russia as 108.9, and with the Jews of Livonia as 120, to 100\nfemale births. But I shall recur to this curious point of the excess\nof male births in the supplement to this chapter. At the Cape of\nGood Hope, however, male children of European extraction have been\nborn during several years in the proportion of between 90 and 99 to\n100 female children.\n For our present purpose we are concerned with the proportions of the\nsexes, not only at birth, but also at maturity, and this adds\nanother element of doubt; for it is a well-ascertained fact that\nwith man the number of males dying before or during birth, and\nduring the first two years of infancy, is considerably larger than\nthat of females. So it almost certainly is with male lambs, and\nprobably with some other animals. The males of some species kill one\nanother by fighting; or they drive one another about until they become\ngreatly emaciated. They must also be often exposed to various dangers,\nwhilst wandering about in eager search for the females. In many\nkinds of fish the males are much smaller than the females, and they\nare believed often to be devoured by the latter, or by other fishes.\nThe females of some birds appear to die earlier than the males; they\nare also liable to be destroyed on their nests, or whilst in charge of\ntheir young. With insects the female larvae are often larger than\nthose of the males, and would consequently be more likely to be\ndevoured. In some cases the mature females are less active and less\nrapid in their movements than the males, and could not escape so\nwell from danger. Hence, with animals in a state of nature, we must\nrely on mere estimation, in order to judge of the proportions of the\nsexes at maturity; and this is but little trustworthy, except when the\ninequality is strongly marked. Nevertheless, as far as a judgment\ncan be formed, we may conclude from the facts given in the supplement,\nthat the males of some few mammals, of many birds, of some fish and\ninsects, are considerably more numerous than the females.\n The proportion between the sexes fluctuates slightly during\nsuccessive years: thus with race-horses, for every 100 mares born\nthe stallions varied from 107.1 in one year to 92.6 in another year,\nand with greyhounds from 116.3 to 95.3. But had larger numbers been\ntabulated throughout an area more extensive than England, these\nfluctuations would probably have disappeared; and such as they are,\nwould hardly suffice to lead to effective sexual selection in a\nstate of nature. Nevertheless, in the cases of some few wild\nanimals, as shewn in the supplement, the proportions seem to fluctuate\neither during different seasons or in different localities in a\nsufficient degree to lead to such selection. For it should be observed\nthat any advantage, gained during certain years or in certain\nlocalities by those males which were able to conquer their rivals,\nor were the most attractive to the females, would probably be\ntransmitted to the offspring, and would not subsequently be\neliminated. During the succeeding seasons, when, from the equality\nof the sexes, every male was able to procure a female, the stronger or\nmore attractive males previously produced would still have at least as\ngood a chance of leaving offspring as the weaker or less attractive.\n Polygamy.- The practice of polygamy leads to the same results as\nwould follow from an actual inequality in the number of the sexes; for\nif each male secures two or more females, many males cannot pair;\nand the latter assuredly will be the weaker or less attractive\nindividuals. Many mammals and some few birds are polygamous, but\nwith animals belonging to the lower classes I have found no evidence\nof this habit. The intellectual powers of such animals are, perhaps,\nnot sufficient to lead them to collect and guard a harem of females.\nThat some relation exists between polygamy and the development of\nsecondary sexual characters, appears nearly certain; and this supports\nthe view that a numerical preponderance of males would be eminently\nfavourable to the action of sexual selection. Nevertheless many\nanimals, which are strictly monogamous, especially birds, display\nstrongly-marked secondary sexual characters; whilst some few\nanimals, which are polygamous, do not have such characters.\n We will first briefly run through the mammals, and then turn to\nbirds. The gorilla seems to be polygamous, and the male differs\nconsiderably from the female; so it is with some baboons, which live\nin herds containing twice as many adult females as males. In South\nAmerica the Mycetes caraya present well-marked sexual differences,\nin colour, beard, and vocal organs; and the male generally lives\nwith two or three wives: the male of the Cebus capucinus differs\nsomewhat from the female, and appears to be polygamous.* Little is\nknown on this head with respect to most other monkeys, but some\nspecies are strictly monogamous. The ruminants are eminently\npolygamous, and they present sexual differences more frequently than\nalmost any other group of mammals; this holds good, especially in\ntheir weapons, but also in other characters. Most deer, cattle, and\nsheep are polygamous; as are most antelopes, though some are\nmonogamous. Sir Andrew Smith, in speaking of the antelopes of South\nAfrica, says that in herds of about a dozen there was rarely more than\none mature male. The Asiatic Antilope saiga appears to be the most\ninordinate polygamist in the world; for Pallas*(2) states that the\nmale drives away all rivals, and collects a herd of about a hundred\nfemales and kids together; the female is hornless and has softer hair,\nbut does not otherwise differ much from the male. The wild horse of\nthe Falkland Islands and of the western states of N. America is\npolygamous, but, except in his greater size and in the proportions\nof his body, differs but little from the mare. The wild boar\npresents well-marked sexual characters, in his great tusks and some\nother points. In Europe and in India he leads a solitary life,\nexcept during the breeding-season; but as is believed by Sir W.\nElliot, who has had many opportunities in India of observing this\nanimal, he consorts at this season with several females. Whether\nthis holds good in Europe is doubtful, but it is supported by some\nevidence. The adult male Indian elephant, like the boar, passes much\nof his time in solitude; but as Dr. Campbell states, when with others,\n\"It is rare to find more than one male with a whole herd of\nfemales\"; the larger males expelling or killing the smaller and weaker\nones. The male differs from the female in his immense tusks, greater\nsize, strength, and endurance; so great is the difference in these\nrespects that the males when caught are valued at one-fifth more\nthan the females.*(3) The sexes of other pachydermatous animals differ\nvery little or not at all, and, as far as known, they are not\npolygamists. Nor have I heard of any species in the Orders of\nCheiroptera, Edentata, Insectivora and rodents being polygamous,\nexcepting that amongst the rodents, the common rat, according to\nsome rat-catchers, lives with several females. Nevertheless the two\nsexes of some sloths (Edentata) differ in the character and colour\nof certain patches of hair on their shoulders.*(4) And many kinds of\nbats (Cheiroptera) present well-marked sexual differences, chiefly\nin the males possessing odoriferous glands and pouches, and by their\nbeing of a lighter colour.*(5) In the great order of rodents, as far\nas I can learn, the sexes rarely differ, and when they do so, it is\nbut slightly in the tint of the fur.\n * On the Gorilla, Savage and Wyman, Boston Journal of Natural\nHistory, vol. v., 1845-47, p. 423. On Cynocephalus, Brehm,\nIllustriertes Thierleben, B. i., 1864, s. 77. On Mycetes, Rengger,\nNaturgeschichte der Saugethiere von Paraguay, 1830, ss. 14, 20. On\nCebus, Brehm, ibid., s. 108.\n *(2) Pallas, Spicilegia Zoolog., fasc. xii., 1777, p. 29. Sir Andrew\nSmith, Illustrations of the Zoology of S. Africa, 1849, pl. 29, on the\nKobus. Owen, in his Anatomy of Vertebrates (vol. iii., 1868, p. 633)\ngives a table shewing incidentally which species of antelopes are\ngregarious.\n *(3) Dr. Campbell, in Proc., Zoolog. Soc., 1869, p. 138. See also an\ninteresting paper by Lieut. Johnstone, in Proceedings, Asiatic Society\nof Bengal, May, 1868.\n *(4) Dr. Gray, in Annals and Magazine of Natural History, 1871, p.\n302.\n *(5) See Dr. Dobson's excellent paper in Proceedings of the\nZoological Society, 1873, p. 241.\n As I hear from Sir Andrew Smith, the lion in South Africa\nsometimes lives with a single female, but generally with more, and, in\none case, was found with as many as five females; so that he is\npolygamous. As far as I can discover, he is the only polygamist\namongst all the terrestrial Carnivora, and he alone presents\nwell-marked sexual characters. If, however, we turn to the marine\nCarnivora, as we shall hereafter see, the case is widely different;\nfor many species of seals offer extraordinary sexual differences,\nand they are eminently polygamous. Thus, according to Peron, the\nmale sea-elephant of the southern ocean always possesses several\nfemales, and the sea-lion of Forster is said to be surrounded by\nfrom twenty to thirty females. In the North, the male sea-bear of\nSteller is accompanied by even a greater number of females. It is an\ninteresting fact, as Dr. Gill remarks,* that in the monogamous\nspecies, \"or those living in small communities, there is little\ndifference in size between the males and females; in the social\nspecies, or rather those of which the males have harems, the males are\nvastly larger than the females.\"\n * \"The Eared Seals,\" American Naturalist, vol. iv., Jan. 1871.\n Amongst birds, many species, the sexes of which differ greatly\nfrom each other, are certainly monogamous. In Great Britain we see\nwell-marked sexual differences, for instance, in the wild-duck which\npairs with a single female, the common blackbird, and the bullfinch\nwhich is said to pair for life. I am informed by Mr. Wallace that\nthe like is true of chatterers or Cotingidae of South America, and\nof many other birds. In several groups I have not been able to\ndiscover whether the species are polygamous or monogamous. Lesson says\nthat birds of paradise, so remarkable for their sexual differences,\nare polygamous, but Mr. Wallace doubts whether he had sufficient\nevidence. Mr. Salvin tells me he has been led to believe that\nhumming-birds are polygamous. The male widow-bird, remarkable for\nhis caudal plumes, certainly seems to be a polygamist.* I have been\nassured by Mr. Jenner Weir and by others, that it is somewhat common\nfor three starlings to frequent the same nest; but whether this is a\ncase of polygamy or polyandry has not been ascertained.\n * The Ibis, vol. iii., 1861, p. 133, on the Progne widow-bird. See\nalso on the Vidua axillaris, ibid., vol. ii., 1860, p. 211. On the\npolygamy of the capercailzie and great bustard, see L. Lloyd, Game\nBirds of Sweden, 1867, pp. 19, and 182. Montagu and Selby speak of the\nblack grouse as polygamous and of the red grouse as monogamous.\n The Gallinaceae exhibit almost as strongly marked sexual differences\nas birds of paradise or humming-birds, and many of the species are, as\nis well know, polygamous; others being strictly monogamous. What a\ncontrast is presented between the sexes of the polygamous peacock or\npheasant, and the monogamous guinea-fowl or partridge! Many similar\ncases could be given, as in the grouse tribe, in which the males of\nthe polygamous capercailzie and black-cock differ greatly from the\nfemales; whilst the sexes of the monogamous red grouse and ptarmigan\ndiffer very little. In the Cursores, except amongst the bustards,\nfew species offer strongly-marked sexual differences, and the great\nbustard (Otis tarda) is said to be polygamous. With the Grallatores,\nextremely few species differ sexually, but the ruff (Machetes\npugnax) affords a marked exception, and this species is believed by\nMontagu to be a polygamist. Hence it appears that amongst birds\nthere often exists a close relation between polygamy and the\ndevelopment of strongly-marked sexual differences. I asked Mr.\nBartlett, of the Zoological Gardens, who has had very large experience\nwith birds, whether the male tragopan (one of the Gallinaceae) was\npolygamous, and I was struck by his answering, \"I do not know, but\nshould think so from his splendid colours.\"\n It deserves notice that the instinct of pairing with a single female\nis easily lost under domestication. The wild-duck is strictly\nmonogamous, the domestic-duck highly polygamous. The Rev. W. D. Fox\ninforms me that out of some half-tamed wild-ducks, on a large pond\nin his neighborhood, so many mallards were shot by the game-keeper\nthat only one was left for every seven or eight females; yet unusually\nlarge broods were reared. The guinea-fowl is strictly monogamous;\nbut Mr. Fox finds that his birds succeed best when he keeps one cock\nto two or three hens. Canary-birds pair in a state of nature, but\nthe breeders in England successfully put one male to four or five\nfemales. I have noticed these cases, as rendering it probable that\nwild monogamous species might readily become either temporarily or\npermanently polygamous.\n Too little is known of the habits of reptiles and fishes to enable\nus to speak of their marriage arrangements. The stickle-back\n(Gasterosteus), however, is said to be a polygamist;* and the male\nduring the breeding-season differs conspicuously from the female.\n * Noel Humphreys, River Gardens, 1857.\n To sum up on the means through which, as far as we can judge, sexual\nselection has led to the development of secondary sexual characters.\nIt has been shewn that the largest number of vigorous offspring will\nbe reared from the pairing of the strongest and best-armed males,\nvictorious in contests over other males, with the most vigorous and\nbest-nourished females, which are the first to breed in the spring. If\nsuch females select the more attractive, and at the same time vigorous\nmales, they will rear a larger number of offspring than the retarded\nfemales, which must pair with the less vigorous and less attractive\nmales. So it will be if the more vigorous males select the more\nattractive and at the same time healthy and vigorous females; and this\nwill especially hold good if the male defends the female, and aids\nin providing food for the young. The advantage thus gained by the more\nvigorous pairs in rearing a larger number of offspring has\napparently sufficed to render sexual selection efficient. But a\nlarge numerical preponderance of males over females will be still more\nefficient; whether the preponderance is only occasional and local,\nor permanent; whether it occurs at birth, or afterwards from the\ngreater destruction of the females; or whether it indirectly follows\nfrom the practice of polygamy.\n The Male generally more modified than the Female.- Throughout the\nanimal kingdom, when the sexes differ in external appearance, it is,\nwith rare exceptions, the male which has been the more modified;\nfor, generally, the female retains a closer resemblance to the young\nof her own species, and to other adult members of the same group.\nThe cause of this seems to lie in the males of almost all animals\nhaving stronger passions than the females. Hence it is the males\nthat fight together and sedulously display their charms before the\nfemales; and the victors transmit their superiority to their male\noffspring. Why both sexes do not thus acquire the characters of\ntheir fathers, will be considered hereafter. That the males of all\nmammals eagerly pursue the females is notorious to every one. So it is\nwith birds; but many cock birds do not so much pursue the hen, as\ndisplay their plumage, perform strange antics, and pour forth their\nsong in her presence. The male in the few fish observed seems much\nmore eager than the female; and the same is true of alligators, and\napparently of batrachians. Throughout the enormous class of insects,\nas Kirby remarks, \"the law is that the male shall seek the female.\"*\nTwo good authorities, Mr. Blackwell and Mr. C. Spence Bate, tell me\nthat the males of spiders and crustaceans are more active and more\nerratic in their habits than the females. When the organs of sense\nor locomotion are present in the one sex of insects and crustaceans\nand absent in the other, or when, as is frequently the case, they\nare more highly developed in the one than in the other, it is, as\nfar as I can discover, almost invariably the male which retains such\norgans, or has them most developed; and this shews that the male is\nthe more active member in the courtship of the sexes.*(2)\n * Kirby and Spence, Introduction to Entomology, vol. iii., 1826,\np. 342.\n *(2) One parasitic hymenopterous insect (Westwood, Modern Class.\nof Insects, vol. ii., p. 160) forms an exception to the rule, as the\nmale has rudimentary wings, and never quits the cell in which it is\nborn, whilst the female has well-developed wings. Audouin believes\nthat the females of this species are impregnated by the males which\nare born in the same cells with them; but it is much more probable\nthat the females visit other cells, so that close inter-breeding is\nthus avoided. We shall hereafter meet in various classes, with a few\nexceptional cases, in which the female, instead of the male, is the\nseeker and wooer.\n The female, on the other hand, with the rarest exceptions, is less\neager than the male. As the illustrious Hunter* long ago observed, she\ngenerally \"requires to be courted\"; she is coy, and may often be\nseen endeavouring for a long time to escape from the male. Every\nobserver of the habits of animals will be able to call to mind\ninstances of this kind. It is shown by various facts, given hereafter,\nand by the results fairly attributable to sexual selection, that the\nfemale, though comparatively passive, generally exerts some choice and\naccepts one male in preference to others. Or she may accept, as\nappearances would sometimes lead us to believe, not the male which\nis the most attractive to her, but the one which is the least\ndistasteful. The exertion of some choice on the part of the female\nseems a law almost as general as the eagerness of the male.\n * Essays and Observations, edited by Owen, vol. i., 1861, p. 194.\n We are naturally led to enquire why the male, in so many and such\ndistinct classes, has become more eager than the female, so that he\nsearches for her, and plays the more active part in courtship. It\nwould be no advantage and some loss of power if each sex searched\nfor the other; but why should the male almost always be the seeker?\nThe ovules of plants after fertilisation have to be nourished for a\ntime; hence the pollen is necessarily brought to the female organs-\nbeing placed on the stigma, by means of insects or the wind, or by the\nspontaneous movements of the stamens; and in the Algae, &c., by the\nlocomotive power of the antherozooids. With lowly-organised aquatic\nanimals, permanently affixed to the same spot and having their sexes\nseparate, the male element is invariably brought to the female; and of\nthis we can see the reason, for even if the ova were detached before\nfertilisation, and did not require subsequent nourishment or\nprotection, there would yet be greater difficulty in transporting them\nthan the male element, because, being larger than the latter, they are\nproduced in far smaller numbers. So that many of the lower animals\nare, in this respect, analogous with plants.* The males of affixed and\naquatic animals having been led to emit their fertilising element in\nthis way, it is natural that any of their descendants, which rose in\nthe scale and became locomotive, should retain the same habit; and\nthey would approach the female as closely as possible, in order not to\nrisk the loss of the fertilising element in a long passage of it\nthrough the water. With some few of the lower animals, the females\nalone are fixed, and the males of these must be the seekers. But it is\ndifficult to understand why the males of species, of which the\nprogenitors were primordially free, should invariably have acquired\nthe habit of approaching the females, instead of being approached by\nthem. But in all cases, in order that the males should seek\nefficiently, it would be necessary that they should be endowed with\nstrong passions; and the acquirement of such passions would\nnaturally follow from the more eager leaving a larger number of\noffspring than the less eager.\n * Prof. Sachs (Lehrbuch der Botanik, 1870, S. 633) in speaking of\nthe male and female reproductive cells, remarks, \"verhalt sich die\neine bei der Vereinigung activ,... die andere erscheint bei der\nVereinigung passiv.\"\n The great eagerness of the males has thus indirectly led to their\nmuch more frequently developing secondary sexual characters than the\nfemales. But the development of such characters would be much aided,\nif the males were more liable to vary than the females- as I concluded\nthey were- after a long study of domesticated animals. Von\nNathusius, who has had very wide experience, is strongly of the same\nopinion.* Good evidence also in favour of this conclusion can be\nproduced by a comparison of the two sexes in mankind. During the\nNovara expedition*(2) a vast number of measurements was made of\nvarious parts of the body in different races, and the men were found\nin almost every case to present a greater range of variation than\nthe women; but I shall have to recur to this subject in a future\nchapter. Mr. J. Wood,*(3) who has carefully attended to the\nvariation of the muscles in man, puts in italics the conclusion that\n\"the greatest number of abnormalities in each subject is found in\nthe males.\" He had previously remarked that \"altogether in 102\nsubjects, the varieties of redundancy were found to be half as many\nagain as in females, contrasting widely with the greater frequency\nof deficiency in females before described.\" Professor Macalister\nlikewise remarks*(4) that variations in the muscles \"are probably more\ncommon in males than females.\" Certain muscles which are not\nnormally present in mankind are also more frequently developed in\nthe male than in the female sex, although exceptions to this rule\nare said to occur. Dr. Burt Wilder*(5) has tabulated the cases of\n152 individuals with supernumerary digits, of which 86 were males, and\n39, or less than half, females, the remaining 27 being of unknown sex.\nIt should not, however, be overlooked that women would more frequently\nendeavour to conceal a deformity of this kind than men. Again, Dr.\nL. Meyer asserts that the ears of man are more variable in form than\nthose of a woman.*(6) Lastly the temperature is more variable in man\nthan in woman.*(7)\n * Vortrage uber Viehzucht, 1872, p. 63.\n *(2) Reise der Novara: Anthropolog. Theil, 1867, ss. 216-269. The\nresults were calculated by Dr. Weisbach from measurements made by Drs.\nK. Scherzer and Schwarz. On the greater variability of the males of\ndomesticated animals, see my Variation of Animals and Plants under\nDomestication, vol. ii., 1868, p. 75.\n *(3) Proceedings of the Royal Society, vol. xvi., July, 1868, pp.\n519 and 524.\n *(4) Proc. Royal Irish Academy, vol. x., 1868, p. 123.\n *(5) Mass. Medical Society, ii., No. 3, 1868, p. 9.\n *(6) Archiv fur Path. Anat. und Phys., 1871, p. 488.\n *(7) The conclusions recently arrived at by Dr. J. Stockton Hough,\non the temperature of man, are given in the Pop. Sci. Review, Jan.\n1, 1874, p. 97.\n The cause of the greater general variability in the male sex, than in\nthe female is unknown, except in so far as secondary sexual characters\nare extraordinarily variable, and are usually confined to the males;\nand, as we shall presently see, this fact is, to a certain extent,\nintelligible. Through the action of sexual and natural selection\nmale animals have been rendered in very many instances widely\ndifferent from their females; but independently of selection the two\nsexes, from differing constitutionally, tend to vary in a somewhat\ndifferent manner. The female has to expend much organic matter in\nthe formation of her ova, whereas the male expends much force in\nfierce contests with his rivals, in wandering about in search of the\nfemale, in exerting his voice, pouring out odoriferous secretions,\n&c.: and this expenditure is generally concentrated within a short\nperiod. The great vigour of the male during the season of love seems\noften to intensify his colours, independently of any marked difference\nfrom the female.* In mankind, and even as low down in the organic\nscale as in the Lepidoptera, the temperature of the body is higher\nin the male than in the female, accompanied in the case of man by a\nslower pulse.*(2) On the whole the expenditure of matter and force\nby the two sexes is probably nearly equal, though effected in very\ndifferent ways and at different rates.\n * Prof. Mantegazza is inclined to believe (\"Lettera a Carlo Darwin,\"\nArchivio per l'Anthropologia, 1871, p. 306) that the bright colours,\ncommon in so many male animals, are due to the presence and\nretention by them of the spermatic fluid; but this can hardly be the\ncase; for many male birds, for instance young pheasants, become\nbrightly coloured in the autumn of their first year.\n *(2) For mankind, see Dr. J. Stockton Hough, whose conclusions are\ngiven in the Popular Science Review, 1874, p. 97. See Girard's\nobservations on the Lepidoptera, as given in the Zoological Record,\n1869, p. 347.\n From the causes just specified the two sexes can hardly fail to\ndiffer somewhat in constitution, at least during the\nbreeding-season; and, although they may be subjected to exactly the\nsame conditions, they will tend to vary in a different manner. If such\nvariations are of no service to either sex, they will not be\naccumulated and increased by sexual or natural selection.\nNevertheless, they may become permanent if the exciting cause acts\npermanently; and in accordance with a frequent form of inheritance\nthey may be transmitted to that sex alone in which they first\nappeared. In this case the two sexes will come to present permanent,\nyet unimportant, differences of character. For instance, Mr. Allen\nshews that with a large number of birds inhabiting the northern and\nsouthern United States, the specimens from the south are\ndarker-coloured than those from the north; and this seems to be the\ndirect result of the difference in temperature, light, &c., between\nthe two regions. Now, in some few cases, the two sexes of the same\nspecies appear to have been differently affected; in the Agelaeus\nphoeniceus the males have had their colours greatly intensified in the\nsouth; whereas with Cardinalis virginianus it is the females which\nhave been thus affected; with Quiscalus major the females have been\nrendered extremely variable in tint, whilst the males remain nearly\nuniform.*\n * Mammals and Birds of E. Florida, pp. 234, 280, 295.\n A few exceptional cases occur in various classes of animals, in\nwhich the females instead of the males have acquired well pronounced\nsecondary sexual characters, such as brighter colours, greater size,\nstrength, or pugnacity. With birds there has sometimes been a complete\ntransposition of the ordinary characters proper to each sex; the\nfemales having become the more eager in courtship, the males remaining\ncomparatively passive, but apparently selecting the more attractive\nfemales, as we may infer from the results. Certain hen birds have thus\nbeen rendered more brightly coloured or otherwise ornamented, as\nwell as more powerful and pugnacious than the cocks; these\ncharacters being transmitted to the female offspring alone.\n It may be suggested that in some cases a double process of selection\nhas been carried on; that the males have selected the more\nattractive females, and the latter the more attractive males. This\nprocess, however, though it might lead to the modification of both\nsexes, would not make the one sex different from the other, unless\nindeed their tastes for the beautiful differed; but this is a\nsupposition too improbable to be worth considering in the case of\nany animal, excepting man. There are, however, many animals in which\nthe sexes resemble each other, both being furnished with the same\nornaments, which analogy would lead us to attribute to the agency of\nsexual selection. In such cases it may be suggested with more\nplausibility, that there has been a double or mutual process of sexual\nselection; the more vigorous and precocious females selecting the more\nattractive and vigorous males, the latter rejecting all except the\nmore attractive females. But from what we know of the habits of\nanimals, this view is hardly probable, for the male is generally eager\nto pair with any female. It is more probable that the ornaments common\nto both sexes were acquired by one sex, generally the male, and then\ntransmitted to the offspring of both sexes. If, indeed, during a\nlengthened period the males of any species were greatly to exceed\nthe females in number, and then during another lengthened period,\nbut under different conditions, the reverse were to occur, a double,\nbut not simultaneous, process of sexual selection might easily be\ncarried on, by which the two sexes might be rendered widely different.\n We shall hereafter see that many animals exist, of which neither sex\nis brilliantly coloured or provided with special ornaments, and yet\nthe members of both sexes or of one alone have probably acquired\nsimple colours, such as white or black, through sexual selection.\nThe absence of bright tints or other ornaments may be the result of\nvariations of the right kind never having occurred, or of the\nanimals themselves having preferred plain black or white. Obscure\ntints have often been developed through natural selection for the sake\nof protection, and the acquirement through sexual selection of\nconspicuous colours, appears to have been sometimes checked from the\ndanger thus incurred. But in other cases the males during long ages\nmay have struggled together for the possession of the females, and yet\nno effect will have been produced, unless a larger number of offspring\nwere left by the more successful males to inherit their superiority,\nthan by the less successful: and this, as previously shewn, depends on\nmany complex contingencies.\n Sexual selection acts in a less rigorous manner than natural\nselection. The latter produces its effects by the life or death at all\nages of the more or less successful individuals. Death, indeed, not\nrarely ensues from the conflicts of rival males. But generally the\nless successful male merely fails to obtain a female, or obtains a\nretarded and less vigorous female later in the season, or, if\npolygamous, obtains fewer females; so that they leave fewer, less\nvigorous, or no offspring. In regard to structures acquired through\nordinary or natural selection, there is in most cases, as long as\nthe conditions of life remain the same, a limit to the amount of\nadvantageous modification in relation to certain special purposes; but\nin regard to structures adapted to make one male victorious over\nanother, either in fighting or in charming the female, there is no\ndefinite limit to the amount of advantageous modification; so that\nas long as the proper variations arise the work of sexual selection\nwill go on. This circumstance may partly account for the frequent\nand extraordinary amount of variability presented by secondary\nsexual characters. Nevertheless, natural selection will determine that\nsuch characters shall not be acquired by the victorious males, if they\nwould be highly injurious, either by expending too much of their vital\npowers, or by exposing them to any great danger. The development,\nhowever, of certain structures- of the horns, for instance, in certain\nstags- has been carried to a wonderful extreme; and in some cases to\nan extreme which, as far as the general conditions of life are\nconcerned, must be slightly injurious to the male. From this fact we\nlearn that the advantages which favoured males derive from\nconquering other males in battle or courtship, and thus leaving a\nnumerous progeny, are in the long run greater than those derived\nfrom rather more perfect adaptation to their conditions of life. We\nshall further see, and it could never have been anticipated, that\nthe power to charm the female has sometimes been more important than\nthe power to conquer other males in battle.\n LAWS OF INHERITANCE.\n In order to understand how sexual selection has acted on many\nanimals of many classes, and in the course of ages has produced a\nconspicuous result, it is necessary to bear in mind the laws of\ninheritance, as far as they are known. Two distinct elements are\nincluded under the term \"inheritance\"- the transmission, and the\ndevelopment of characters; but as these generally go together, the\ndistinction is often overlooked. We see this distinction in those\ncharacters which are transmitted through the early years of life,\nbut are developed only at maturity or during old age. We see the\nsame distinction more clearly with secondary sexual characters, for\nthese are transmitted through both sexes, though developed in one\nalone. That they are present in both sexes, is manifest when two\nspecies, having strongly-marked sexual characters, are crossed, for\neach transmits the characters proper to its own male and female sex to\nthe hybrid offspring of either sex. The same fact is likewise\nmanifest, when characters proper to the male are occasionally\ndeveloped in the female when she grows old or becomes diseased, as,\nfor instance, when the common hen assumes the flowing tail-feathers,\nhackles, comb, spurs, voice, and even pugnacity of the cock.\nConversely, the same thing is evident, more or less plainly, with\ncastrated males. Again, independently of old age or disease,\ncharacters are occasionally transferred from the male to the female,\nas when, in certain breeds of the fowl, spurs regularly appear in\nthe young and healthy females. But in truth they are simply\ndeveloped in the female; for in every breed each detail in the\nstructure of the spur is transmitted through the female to her male\noffspring. Many cases will hereafter be given, where the female\nexhibits, more or less perfectly, characters proper to the male, in\nwhom they must have been first developed, and then transferred to\nthe female. The converse case of the first development of characters\nin the female and of transference to the male, is less frequent; it\nwill therefore be well to give one striking instance. With bees the\npollen-collecting apparatus is used by the female alone for\ngathering pollen for the larvae, yet in most of the species it is\npartially developed in the males to whom it is quite useless, and it\nis perfectly developed in the males of Bombus or the humble-bee.* As\nnot a single other hymenopterous insect, not even the wasp, which is\nclosely allied to the bee, is provided with a pollen-collecting\napparatus, we have no grounds for supposing that male bees\nprimordially collected pollen as well as the females; although we have\nsome reason to suspect that male mammals primordially suckled their\nyoung as well as the females. Lastly, in all cases of reversion,\ncharacters are transmitted through two, three, or many more\ngenerations, and are then developed under certain unknown favourable\nconditions. This important distinction between transmission and\ndevelopment will be best kept in mind by the aid of the hypothesis\nof pangenesis. According to this hypothesis, every unit or cell of the\nbody throws off gemmules or undeveloped atoms, which are transmitted\nto the offspring of both sexes, and are multiplied by self-division.\nThey may remain undeveloped during the early years of life or during\nsuccessive generations; and their development into units or cells,\nlike those from which they were derived, depends on their affinity\nfor, and union with other units or cells previously developed in the\ndue order of growth.\n * H. Muller, \"Anwendung der Darwin'schen Lehre, &c.,\" Verh. d. n. V.\nJahrg., xxix. p. 42.\n Inheritance at corresponding Periods of Life.- This tendency is well\nestablished. A new character, appearing in a young animal, whether\nit lasts throughout life or is only transient, will, in general,\nreappear in the offspring at the same age and last for the same\ntime. If, on the other hand, a new character appears at maturity, or\neven during old age, it tends to reappear in the offspring at the same\nadvanced age. When deviations from this rule occur, the transmitted\ncharacters much oftener appear before, than after the corresponding\nage. As I have dwelt on this subject sufficiently in another work,*\nI will here merely give two or three instances, for the sake of\nrecalling the subject to the reader's mind. In several breeds of the\nfowl, the down-covered chickens, the young birds in their first true\nplumage, and the adults differ greatly from one another, as well as\nfrom their common parent-form, the Gallus bankiva; and these\ncharacters are faithfully transmitted by each breed to their offspring\nat the corresponding periods of life. For instance, the chickens of\nspangled Hamburgs, whilst covered with down have a few dark spots on\nthe head and rump, but are not striped longitudinally, as in many\nother breeds; in their first true plumage, \"they are beautifully\npencilled,\" that is each feather is transversely marked by numerous\ndark bars; but in their second plumage the feathers all become\nspangled or tipped with a dark round spot.*(2) Hence in this breed\nvariations have occurred at, and been transmitted to, three\ndistinct periods of life. The pigeon offers a more remarkable case,\nbecause the aboriginal parent species does not undergo any change of\nplumage with advancing age, excepting that at maturity the breast\nbecomes more iridescent; yet there are breeds which do not acquire\ntheir characteristic colours until they have moulted two, three, or\nfour times; and these modifications of plumage are regularly\ntransmitted.\n * The Variation of Animals and Plants under Domestication, vol. ii.,\n1868, p. 75. In the last chapter but one, the provisional hypothesis\nof pangenesis, above alluded to, is fully explained.\n *(2) These facts are given on the high authority of a great breeder,\nMr. Teebay; see Tegetmeier's Poultry Book, 1868, p. 158. On the\ncharacters of chickens of different breeds, and on the breeds of the\npigeon, alluded to in the following paragraph, see Variation of\nAnimals, &c., vol. i., pp. 160, 249; vol. ii., p. 77.\n Inheritance at corresponding Seasons of the Year.- With animals in a\nstate of nature, innumerable instances occur of characters appearing\nperiodically at different seasons. We see this in the horns of the\nstag, and in the fur of arctic animals which becomes thick and white\nduring the winter. Many birds acquire bright colours and other\ndecorations during the breeding-season alone. Pallas states,* that\nin Siberia domestic cattle and horses become lighter-coloured during\nthe winter; and I have myself observed, and heard of similar\nstrongly marked changes of colour, that is, from brownish cream-colour\nor reddish-brown to a perfect white, in several ponies in England.\nAlthough I do not know that this tendency to change the colour of\nthe coat during different seasons is transmitted, yet it probably is\nso, as all shades of colour are strongly inherited by the horse. Nor\nis this form of inheritance, as limited by the seasons, more\nremarkable than its limitation by age or sex.\n * Novae species Quadrupedum e Glirium ordine, 1778, p. 7. On the\ntransmission of colour by the horse, see Variation of Animals and\nPlants under Domestication, vol. i., p. 51. Also vol. ii., p. 71,\nfor a general discussion on \"Inheritance as limited by Sex.\"\n Inheritance as Limited by Sex.- The equal transmission of characters\nto both sexes is the commonest form of inheritance, at least with\nthose animals which do not present strongly-marked sexual differences,\nand indeed with many of these. But characters are somewhat commonly\ntransferred exclusively to that sex, in which they first appear. Ample\nevidence on this head has been advanced in my work on Variation\nunder Domestication, but a few instances may here be given. There\nare breeds of the sheep and goat, in which the horns of the male\ndiffer greatly in shape from those of the female; and these\ndifferences, acquired under domestication, are regularly transmitted\nto the same sex. As a rule, it is the females alone in cats which\nare tortoise-shell, the corresponding colour in the males being\nrusty-red. With most breeds of the fowl, the characters proper to each\nsex are transmitted to the same sex alone. So general is this form\nof transmission that it is an anomaly when variations in certain\nbreeds are transmitted equally to both sexes. There are also certain\nsub-breeds of the fowl in which the males can hardly be\ndistinguished from one another, whilst the females differ considerably\nin colour. The sexes of the pigeon in the parent-species do not differ\nin any external character; nevertheless, in certain domesticated\nbreeds the male is coloured differently from the female.* The wattle\nin the English carrier pigeon, and the crop in the pouter, are more\nhighly developed in the male than in the female; and although these\ncharacters have been gained through long-continued selection by man,\nthe slight differences between the sexes are wholly due to the form of\ninheritance which has prevailed; for they have arisen, not from, but\nrather in opposition to, the wish of the breeder.\n * Dr. Chapuis, Le Pigeon Voyageur Belge, 1865, p. 87. Boitard et\nCorbie, Les Pigeons de Voliere, &c., 1824, p. 173. See, also, on\nsimilar differences in certain breeds at Modena, Le variazioni dei\nColombi domestici, del Paolo Bonizzi, 1873.\n Most of our domestic races have been formed by the accumulation of\nmany slight variations; and as some of the successive steps have\nbeen transmitted to one sex alone, and some to both sexes, we find\nin the different breeds of the same species all gradations between\ngreat sexual dissimilarity and complete similarity. Instances have\nalready been given with the breeds of the fowl and pigeon, and under\nnature analogous cases are common. With animals under domestication,\nbut whether in nature I will not venture to say, one sex may lose\ncharacters proper to it, and may thus come somewhat to resemble the\nopposite sex; for instance, the males of some breeds of the fowl\nhave lost their masculine tail-plumes and hackles. On the other\nhand, the differences between the sexes may be increased under\ndomestication, as with merino sheep, in which the ewes have lost their\nhorns. Again, characters proper to one sex may suddenly appear in\nthe other sex; as in those sub-breeds of the fowl in which the hens\nacquire spurs whilst young; or, as in certain Polish sub-breeds, in\nwhich the females, as there is reason to believe, originally\nacquired a crest, and subsequently transferred it to the males. All\nthese cases are intelligible on the hypothesis of pangenesis; for they\ndepend on the gemmules of certain parts, although present in both\nsexes, becoming, through the influence of domestication, either\ndormant or developed in either sex.\n There is one difficult question which it will be convenient to defer\nto a future chapter; namely, whether a character at first developed in\nboth sexes, could through selection be limited in its development to\none sex alone. If, for instance, a breeder observed that some of his\npigeons (of which the characters are usually transferred in an equal\ndegree to both sexes) varied into pale blue, could he by\nlong-continued selection make a breed, in which the males alone should\nbe of this tint, whilst the females remained unchanged? I will here\nonly say, that this, though perhaps not impossible, would be extremely\ndifficult; for the natural result of breeding from the pale-blue males\nwould be to change the whole stock of both sexes to this tint. If,\nhowever, variations of the desired tint appeared, which were from\nthe first limited in their development to the male sex, there would\nnot be the least difficulty in making a breed with the two sexes of\na different colour, as indeed has been effected with a Belgian\nbreed, in which the males alone are streaked with black. In a\nsimilar manner, if any variation appeared in a female pigeon, which\nwas from the first sexually limited in its development to the females,\nit would be easy to make a breed with the females alone thus\ncharacterised; but if the variation was not thus originally limited,\nthe process would be extremely difficult, perhaps impossible.*\n * Since the publication of the first edition of this work, it has\nbeen highly satisfactory to me to find the following remarks (the\nField, Sept., 1872) from so experienced a breeder as Mr. Tegetmeier.\nAfter describing some curious cases in pigeons, of the transmission of\ncolour by one sex alone, and the formation of a sub-breed with this\ncharacter, he says: \"It is a singular circumstance that Mr. Darwin\nshould have suggested the possibility of modifying the sexual\ncolours of birds by a course of artificial selection. When he did\nso, he was in ignorance of these facts that I have related; but it\nis remarkable how very closely he suggested the right method of\nprocedure.\"\n On the Relation between the Period of Development of a Character and\nits Transmission to one Sex or to both Sexes.- Why certain\ncharacters should be inherited by both sexes, and other characters\nby one sex alone, namely by that sex in which the character first\nappeared, is in most cases quite unknown. We cannot even conjecture\nwhy with certain sub-breeds of the pigeon, black striae, though\ntransmitted through the female, should be developed in the male alone,\nwhilst every other character is equally transferred to both sexes.\nWhy, again, with cats, the tortoise-shell colour should, with rare\nexceptions, be developed in the female alone. The very same character,\nsuch as deficient or super-numerary digits, colour-blindness, &c., may\nwith mankind be inherited by the males alone of one family, and in\nanother family by the females alone, though in both cases\ntransmitted through the opposite as well as through the same sex.*\nAlthough we are thus ignorant, the two following rules seem often to\nhold good- that variations which first appear in either sex at a\nlate period of life tend to be developed in the same sex alone; whilst\nvariations which first appear early in life in either sex tend to be\ndeveloped in both sexes. I am, however, far from supposing that this\nis the sole determining cause. As I have not elsewhere discussed\nthis subject, and it has an important bearing on sexual selection, I\nmust here enter into lengthy and somewhat intricate details.\n * References are given in my Variation of Animals and Plants under\nDomestication, vol. ii., p. 72.\n It is in itself probable that any character appearing at an early\nage would tend to be inherited equally by both sexes, for the sexes do\nnot differ much in constitution before the power of reproduction is\ngained. On the other hand, after this power has been gained and the\nsexes have come to differ in constitution, the gemmules (if I may\nagain use the language of pangenesis) which are cast off from each\nvarying part in the one sex would be much more likely to possess the\nproper affinities for uniting with the tissues of the same sex, and\nthus becoming developed, than with those of the opposite sex.\n I was first led to infer that a relation of this kind exists, from\nthe fact that whenever and in whatever manner the adult male differs\nfrom the adult female, he differs in the same manner from the young of\nboth sexes. The generality of this fact is quite remarkable: it\nholds good with almost all mammals, birds, amphibians, and fishes;\nalso with many crustaceans, spiders, and some few insects, such as\ncertain Orthoptera and Libellulae. In all these cases the\nvariations, through the accumulation of which the male acquired his\nproper masculine characters, must have occurred at a somewhat late\nperiod of life; otherwise the young males would have been similarly\ncharacterised; and conformably with our rule, the variations are\ntransmitted to and developed in the adult males alone. When, on the\nother hand, the adult male closely resembles the young of both sexes\n(these, with rare exceptions, being alike), he generally resembles the\nadult female; and in most of these cases the variations through\nwhich the young and old acquired their present characters, probably\noccurred, according to our rule, during youth. But there is here\nroom for doubt, for characters are sometimes transferred to the\noffspring at an earlier age than that at which they first appeared\nin the parents, so that the parents may have varied when adult, and\nhave transferred their characters to their offspring whilst young.\nThere are, moreover, many animals, in which the two sexes closely\nresemble each other, and yet both differ from their young: and here\nthe characters of the adults must have been acquired late in life;\nnevertheless, these characters, in apparent contradiction to our rule,\nare transferred to both sexes. We must not however, overlook the\npossibility or even probability of successive variations of the same\nnature occurring, under exposure to similar conditions, simultaneously\nin both sexes at a rather late period of life; and in this case the\nvariations would be transferred to the offspring of both sexes at a\ncorresponding late age; and there would then be no real\ncontradiction to the rule that variations occurring late in life are\ntransferred exclusively to the sex in which they first appeared.\nThis latter rule seems to hold true more generally than the second\none, namely, that variations which occur in either sex early in life\ntend to be transferred to both sexes. As it was obviously impossible\neven to estimate in how large a number of cases throughout the\nanimal kingdom these two propositions held good, it occurred to me\nto investigate some striking or crucial instances, and to rely on\nthe result.\n An excellent case for investigation is afforded by the deer\nfamily. In all the species, but one, the horns are developed only in\nthe males, though certainly transmitted through the females, and\ncapable of abnormal development in them. In the reindeer, on the other\nhand, the female is provided with horns; so that in this species,\nthe horns ought, according to our rule, to appear early in life,\nlong before the two sexes are mature and have come to differ much in\nconstitution. In all the other species the horns ought to appear later\nin life, which would lead to their development in that sex alone, in\nwhich they first appeared in the progenitor of the whole family. Now\nin seven species, belonging to distinct sections of the family and\ninhabiting different regions, in which the stags alone bear horns, I\nfind that the horns first appear at periods, varying from nine\nmonths after birth in the roebuck to ten, twelve or even more months\nin the stags of the six other and larger species.* But with the\nreindeer the case is widely different; for, as I hear from Prof.\nNilsson, who kindly made enquiries for me in Lapland, the horns appear\nin the young animals within four or five weeks after birth, and at the\nsame time in both sexes. So that here we have a structure, developed\nat a most unusually early age in one species of the family, and\nlikewise common to both sexes in this one species alone.\n * I am much obliged to Mr. Cupples for having made enquiries for\nme in regard to the roebuck and red deer of Scotland from Mr.\nRobertson, the experienced head-forester to the Marquis of\nBreadalbane. In regard to fallow-deer, I have to thank Mr. Eyton and\nothers for information. For the Cervus alces of N. America, see Land\nand Water, 1868, pp. 221 and 254; and for the C. Virginianus and C.\nstrongyloceros of the same continent, see J. D. Caton, in Ottawa Acad.\nof Nat. Sc., 1868, p. 13. For Cervus eldi of Pegu, see Lieut.\nBeaven, Proccedings of the Zoological Society, 1867, p. 762.\n In several kinds of antelopes, only the males are provided with\nhorns, whilst in the greater number both sexes bear horns. With\nrespect to the period of development, Mr. Blyth informs me that\nthere was at one time in the Zoological Gardens a young koodoo (A.\nstrepsiceros), of which the males alone are horned, and also the young\nof a closely-allied species, the eland (A. oreas), in which both sexes\nare horned. Now it is in strict conformity with our rule, that in\nthe young male koodoo, although ten months old, the horns were\nremarkably small, considering the size ultimately attained by them;\nwhilst in the young male eland, although only three months old, the\nhorns were already very much larger than in the koodoo. It is also a\nnoticeable fact that in the prong-horned antelope,* only a few of\nthe females, about one in five, have horns, and these are in a\nrudimentary state, though sometimes above four inches long: so that as\nfar as concerns the possession of horns by the males alone, this\nspecies is in an intermediate condition, and the horns do not appear\nuntil about five or six months after birth. Therefore in comparison\nwith what little we know of the development of the horns in other\nantelopes, and from what we do know with respect to the horns of deer,\ncattle, &c., those of the prong-horned antelope appear at an\nintermediate period of life,- that is, not very early, as in cattle\nand sheep, nor very late, as in the larger deer and antelopes. The\nhorns of sheep, goats, and cattle, which are well developed in both\nsexes, though not quite equal in size, can be felt, or even seen, at\nbirth or soon afterwards.*(2) Our rule, however, seems to fail in some\nbreeds of sheep, for instance merinos, in which the rams alone are\nhorned; for I cannot find on enquiry,*(3) that the horns are developed\nlater in life in this breed than in ordinary sheep in which both sexes\nare horned. But with domesticated sheep the presence or absence of\nhorns is not a firmly fixed character; for a certain proportion of the\nmerino ewes bear small horns, and some of the rams are hornless; and\nin most breeds hornless ewes are occasionally produced.\n * Antilocapra Americana. I have to thank Dr. Canfield for\ninformation with respect to the horns of the female: see also his\npaper in Proceedings of the Zoological Society, 1866, p. 109. Also\nOwen, Anatomy of Vertebrates, vol. iii., p. 627.\n *(2) I have been assured that the horns of the sheep in north\nWales can always be felt, and are sometimes even an inch in length, at\nbirth. Youatt says (Cattle, 1834, p. 277), that the prominence of\nthe frontal bone in cattle penetrates the cutis at birth, and that the\nhorny matter is soon formed over it.\n *(3) I am greatly indebted to Prof. Victor Carus for having made\nenquiries for me, from the highest authorities, with respect to the\nmerino sheep of Saxony. On the Guinea coast of Africa there is,\nhowever, a breed of sheep in which, as with merinos, the rams alone\nbear horns; and Mr. Winwood Reade informs me that in one case observed\nby him, a young ram, born on Feb. 10th, first shewed horns on March\n6th, so that in this instance, in conformity with rule, the\ndevelopment of the horns occurred at a later period of life than in\nWelsh sheep, in which both sexes are horned.\n Dr. W. Marshall has lately made a special study of the protuberances\nso common on the heads of birds,* and he comes to the following\nconclusion:- that with those species in which they are confined to the\nmales, they are developed late in life; whereas with those species\nin which they are common to the two sexes, they are developed at a\nvery early period. This is certainly a striking confirmation of my two\nlaws of inheritance.\n * \"Uber die knochernen Schadelhocker der Vogel\", in the\nNiederland. Archiv fur Zoologie, B.i., Heft 2, 1872.\n In most of the species of the splendid family of the pheasants,\nthe males differ conspicuously from the females, and they acquire\ntheir ornaments at a rather late period of life. The eared pheasant\n(Crossoptilon auritum), however, offers a remarkable exception, for\nboth sexes possess the fine caudal plumes, the large ear-tufts and the\ncrimson velvet about the head; I find that all these characters appear\nvery early in life in accordance with rule. The adult male can,\nhowever, be distinguished from the adult female by the presence of\nspurs; and conformably with our rule, these do not begin to be\ndeveloped before the age of six months, as I am assured by Mr.\nBartlett, and even at this age, the two sexes can hardly be\ndistinguished.* The male and female peacock differ conspicuously\nfrom each other in almost every part of their plumage, except in the\nelegant head-crest, which is common to both sexes; and this is\ndeveloped very early in life, long before the other ornaments, which\nare confined to the male. The wild-duck offers an analogous case,\nfor the beautiful green speculum on the wings is common to both sexes,\nthough duller and somewhat smaller in the female, and it is\ndeveloped early in life, whilst the curled tail-feathers and other\nornaments of the male are developed later.*(2) Between such extreme\ncases of close sexual resemblance and wide dissimilarity, as those\nof the Crossoptilon and peacock, many intermediate ones could be\ngiven, in which the characters follow our two rules in their order\nof development.\n * In the common peacock (Pavo cristatus) the male alone possesses\nspurs, whilst both sexes of the Java peacock (P. muticus) offer the\nunusual case of being furnished with spurs. Hence I fully expected\nthat in the latter species they would have been developed earlier in\nlife than in the common peacock; but M. Hegt of Amsterdam informs\nme, that with young birds of the previous year, of both species,\ncompared on April 23rd, 1869, there was no difference in the\ndevelopment of the spurs. The spurs, however, were as yet\nrepresented merely by slight knobs or elevations. I presume that I\nshould have been informed if any difference in the rate of development\nhad been observed subsequently.\n *(2) In some other species of the duck family the speculum differs\nin a greater degree in the two sexes; but I have not been able to\ndiscover whether its full development occurs later in life in the\nmales of such species, than in the male of the common duck, as ought\nto be the case according to our rule. With the allied Mergus\ncucullatus we have, however, a case of this kind: the two sexes differ\nconspicuously in general plumage, and to a considerable degree in\nthe speculum, which is pure white in the male and greyish-white in the\nfemale. Now the young males at first entirely resemble the females,\nand have a greyish-white speculum, which becomes pure white at an\nearlier age than that at which the adult male acquires his other and\nmore strongly-marked sexual differences: see Audubon, Ornithological\nBiography, vol. iii., 1835, pp. 249-250.\n As most insects emerge from the pupal state in a mature condition,\nit is doubtful whether the period of development can determine the\ntransference of their characters to one or to both sexes. But we do\nnot know that the coloured scales, for instance, in two species of\nbutterflies, in one of which the sexes differ in colour, whilst in the\nother they are alike, are developed at the same relative age in the\ncocoon. Nor do we know whether all the scales are simultaneously\ndeveloped on the wings of the same species of butterfly, in which\ncertain coloured marks are confined to one sex, whilst others are\ncommon to both sexes. A difference of this kind in the period of\ndevelopment is not so improbable as it may at first appear; for with\nthe Orthoptera, which assume their adult state, not by a single\nmetamorphosis, but by a succession of moults, the young males of\nsome species at first resemble the females, and acquire their\ndistinctive masculine characters only at a later moult. Strictly\nanalogous cases occur at the successive moults of certain male\ncrustaceans.\n We have as yet considered the transference of characters, relatively\nto their period of development, only in species in a natural state; we\nwill now turn to domesticated animals, and first touch on\nmonstrosities and diseases. The presence of supernumerary digits,\nand the absence of certain phalanges, must be determined at an early\nembryonic period- the tendency to profuse bleeding is at least\ncongenital, as is probably colour-blindness- yet these\npeculiarities, and other similar ones, are often limited in their\ntransmission to one sex; so that the rule that characters, developed\nat an early period, tend to be transmitted to both sexes, here\nwholly fails. But this rule, as before remarked, does not appear to be\nnearly so general as the converse one, namely, that characters which\nappear late in life in one sex are transmitted exclusively to the same\nsex. From the fact of the above abnormal peculiarities becoming\nattached to one sex, long before the sexual functions are active, we\nmay infer that there must be some difference between the sexes at an\nextremely early age. With respect to sexually-limited diseases, we\nknow too little of the period at which they originate, to draw any\nsafe conclusion. Gout, however, seems to fall under our rule, for it\nis generally caused by intemperance during manhood, and is transmitted\nfrom the father to his sons in a much more marked manner than to his\ndaughters.\n In the various domestic breeds of sheeps, goats, and cattle, the\nmales differ from their respective females in the shape or development\nof their horns, forehead, mane, dewlap, tail, and hump on the\nshoulders; and these peculiarities, in accordance with our rule, are\nnot fully developed until a rather late period of life. The sexes of\ndogs do not differ, except that in certain breeds, especially in the\nScotch deerhound, the male is much larger and heavier than the female;\nand, as we shall see in a future chapter, the male goes on\nincreasing in size to an unusually late period of life, which,\naccording to rule, will account for his increased size being\ntransmitted to his male offspring alone. On the other hand, the\ntortoise-shell colour, which is confined to female cats, is quite\ndistinct at birth, and this case violates the rule. There is a breed\nof pigeons in which the males alone are streaked with black, and the\nstreaks can be detected even in the nestlings; but they become more\nconspicuous at each successive moult, so that this case partly opposes\nand partly supports the rule. With the English carrier and pouter\npigeons, the full development of the wattle and the crop occurs rather\nlate in life, and conformably with the rule, these characters are\ntransmitted in full perfection to the males alone. The following cases\nperhaps come within the class previously alluded to, in which both\nsexes have varied in the same manner at a rather late period of\nlife, and have consequently transferred their new characters to both\nsexes at a corresponding late period; and if so, these cases are not\nopposed to our rule:- there exist sub-breeds of the pigeon,\ndescribed by Neumeister,* in which both sexes change their colour\nduring two or three moults (as is likewise the case with the almond\ntumbler); nevertheless, these changes, though occurring rather late in\nlife, are common to both sexes. One variety of the canary-bird, namely\nthe London Prize, offers a nearly analogous case.\n * Das Ganze der Taubenzucht, 1837, ss. 21, 24. For the case of the\nstreaked pigeons, see Dr. Chapuis, Le Pigeon Voyageur Belge, 1855,\np. 87.\n With the breeds of the fowl the inheritance of various characters by\none or both sexes, seems generally determined by the period at which\nsuch characters are developed. Thus in all the many breeds in which\nthe adult male differs greatly in colour from the female, as well as\nfrom the wild parent-species, he differs also from the young male,\nso that the newly-acquired characters must have appeared at a rather\nlate period of life. On the other hand, in most of the breeds in which\nthe two sexes resemble each other, the young are coloured in nearly\nthe same manner as their parents, and this renders it probable that\ntheir colours first appeared early in life. We have instances of\nthis fact in all black and white breeds, in which the young and old of\nboth sexes are alike; nor can it be maintained that there is something\npeculiar in a black or white plumage, which leads to its\ntransference to both sexes; for the males alone of many natural\nspecies are either black or white, the females being differently\ncoloured. With the so-called cuckoo sub-breeds of the fowl, in which\nthe feathers are transversely pencilled with dark stripes, both\nsexes and the chickens are coloured in nearly the same manner. The\nlaced plumage of the Sebright bantam is the same in both sexes, and in\nthe young chickens the wing-feathers are distinctly, though\nimperfectly laced. Spangled Hamburgs, however, offer a partial\nexception; for the two sexes, though not quite alike, resemble each\nother more closely than do the sexes of the aboriginal parent-species;\nyet they acquire their characteristic plumage late in life, for the\nchickens are distinctly pencilled. With respect to other characters\nbeside colour, in the wild-parent species and in most of the\ndomestic breeds, the males alone possess a well-developed comb; but in\nthe young of the Spanish fowl it is largely developed at a very\nearly age, and, in accordance with this early development in the male,\nit is of unusual size in the adult female. In the game breeds\npugnacity is developed at a wonderfully early age, of which curious\nproofs could be given; and this character is transmitted to both\nsexes, so that the hens, from their extreme pugnacity, are now\ngenerally exhibited in separate pens. With the Polish breeds the\nbony protuberance of the skull which supports the crest is partially\ndeveloped even before the chickens are hatched, and the crest itself\nsoon begins to grow, though at first feebly;* and in this breed the\nadults of both sexes are characterised by a great bony protuberance\nand an immense crest.\n * For full particulars and references on all these points respecting\nthe several breeds of the fowl, see Variation of Animals and Plants\nunder Domestication, vol. i., pp. 250, 256. In regard to the higher\nanimals, the sexual differences which have arisen under\ndomestication are described in the same work under the head of each\nspecies.\n Finally, from what we have now seen of the relation which exists\nin many natural species and domesticated races, between the period\nof the development of their characters and the manner of their\ntransmission- for example, the striking fact of the early growth of\nthe horns in the reindeer, in which both sexes bear horns, in\ncomparison with their much later growth in the other species in\nwhich the male alone bears horns- we may conclude that one, though not\nthe sole cause of characters being exclusively inherited by one sex,\nis their development at a late age. And secondly, that one, though\napparently a less efficient cause of characters being inherited by\nboth sexes, is their development at an early age, whilst the sexes\ndiffer but little in constitution. It appears, however, that some\ndifference must exist between the sexes even during a very early\nembryonic period, for characters developed at this age not rarely\nbecome attached to one sex.\n Summary and concluding remarks.- From the foregoing discussion on\nthe various laws of inheritance, we learn that the characters of the\nparents often, or even generally, tend to become developed in the\noffspring of the same sex, at the same age, and periodically at the\nsame season of the year, in which they first appeared in the\nparents. But these rules, owing to unknown causes, are far from\nbeing fired. Hence during the modification of a species, the\nsuccessive changes may readily be transmitted in different ways;\nsome to one sex, and some to both; some to the offspring at one age,\nand some to the offspring at all ages. Not only are the laws of\ninheritance extremely complex, but so are the causes which induce\nand govern variability. The variations thus induced are preserved\nand accumulated by sexual selection, which is in itself an extremely\ncomplex affair, depending, as it does, on the ardour in love, the\ncourage, and the rivalry of the males, as well as on the powers of\nperception, the taste, and will of the female. Sexual selection will\nalso be largely dominated by natural selection tending towards the\ngeneral welfare of the species. Hence the manner in which the\nindividuals of either or both sexes have been affected through\nsexual selection cannot fail to be complex in the highest degree.\n When variations occur late in life in one sex, and are transmitted\nto the same sex at the same age, the other sex and the young are\nleft unmodified. When they occur late in life, but are transmitted\nto both sexes at the same age, the young alone are left unmodified.\nVariations, however, may occur at any period of life in one sex or\nin both, and be transmitted to both sexes at all ages, and then all\nthe individuals of the species are similarly modified. In the\nfollowing chapters it will be seen that all these cases frequently\noccur in nature.\n Sexual selection can never act on any animal before the age for\nreproduction arrives. From the great eagerness of the male it has\ngenerally acted on this sex and not on the females. The males have\nthus become provided with weapons for fighting with their rivals, with\norgans for discovering and securely holding the female, and for\nexciting or charming her. When the sexes differ in these respects,\nit is also, as we have seen, an extremely general law that the adult\nmale differs more or less from the young male; and we may conclude\nfrom this fact that the successive variations, by which the adult male\nbecame modified, did not generally occur much before the age for\nreproduction. Whenever some or many of the variations occurred early\nin life, the young males would partake more or less of the\ncharacters of the adult males; and differences of this kind between\nthe old and young males may be observed in many species of animals.\n It is probable that young male animals have often tended to vary\nin a manner which would not only have been of no use to them at an\nearly age, but would have been actually injurious- as by acquiring\nbright colours, which would render them conspicuous to their\nenemies, or by acquiring structures, such as great horns, which\nwould expend much vital force in their development. Variations of this\nkind occurring in the young males would almost certainly be eliminated\nthrough natural selection. With the adult and experienced males, on\nthe other hand, the advantages derived from the acquisition of such\ncharacters, would more than counterbalance some exposure to danger,\nand some loss of vital force.\n As variations which give to the male a better chance of conquering\nother males, or of finding, securing, or charming the opposite sex,\nwould, if they happened to arise in the female, be of no service to\nher, they would not be preserved in her through sexual selection. We\nhave also good evidence with domesticated animals, that variations\nof all kinds are, if not carefully selected, soon lost through\ninter-crossing and accidental deaths. Consequently in a state of\nnature, if variations of the above kind chanced to arise in the female\nline, and be transmitted exclusively in this line, they would be\nextremely liable to be lost. If, however, the females varied and\ntransmitted their newly acquired characters to their offspring of both\nsexes, the characters which were advantageous to the males would be\npreserved by them through sexual selection, and the two sexes would in\nconsequence be modified in the same manner, although such characters\nwere of no use to the females: but I shall hereafter have to recur\nto these more intricate contingencies. Lastly, the females may\nacquire, and apparently have often acquired by transference,\ncharacters from the male sex.\n As variations occurring later in life, and transmitted to one sex\nalone, have incessantly been taken advantage of and accumulated\nthrough sexual selection in relation to the reproduction of the\nspecies; therefore it appears, at first sight, an unaccountable fact\nthat similar variations have not frequently been accumulated through\nnatural selection, in relation to the ordinary habits of life. If this\nhad occurred, the two sexes would often have been differently\nmodified, for the sake, for instance, of capturing prey or of escaping\nfrom danger. Differences of this kind between the two sexes do\noccasionally occur, especially in the lower classes. But this\nimplies that the two sexes follow different habits in their\nstruggles for existence, which is a rare circumstance with the\nhigher animals. The case, however, is widely different with the\nreproductive functions, in which respect the sexes necessarily differ.\nFor variations in structure which are related to these functions, have\noften proved of value to one sex, and from having arisen at a late\nperiod of life, have been transmitted to one sex alone; and such\nvariations, thus preserved and transmitted, have given rise to\nsecondary sexual characters.\n In the following chapters, I shall treat of the secondary sexual\ncharacters in animals of all classes, and shall endeavour in each case\nto apply the principles explained in the present chapter. The lowest\nclasses will detain us for a very short time, but the higher\nanimals, especially birds, must be treated at considerable length.\nIt should be borne in mind that for reasons already assigned, I intend\nto give only a few illustrative instances of the innumerable\nstructures by the aid of which the male finds the female, or, when\nfound, holds her. On the other hand, all structures and instincts by\nthe aid of which the male conquers other males, and by which he\nallures or excites the female, will be fully discussed, as these are\nin many ways the most interesting.\n Supplement on the proportional numbers of the two sexes in animals\nbelonging to various classes.\n As no one, as far as I can discover, has paid attention to the\nrelative numbers of the two sexes throughout the animal kingdom, I\nwill here give such materials as I have been able to collect, although\nthey are extremely imperfect. They consist in only a few instances\nof actual enumeration, and the numbers are not very large. As the\nproportions are known with certainty only in mankind, I will first\ngive them as a standard of comparison.\n Man.- In England during ten years (from 1857 to 1866) the average\nnumber of children born alive yearly was 707,120, in the proportion of\n104.5 males to 100 females. But in 1857 the male births throughout\nEngland were as 105.2, and in 1865 as 104.0 to 100. Looking to\nseparate districts, in Buckinghamshire (where about 5000 children\nare annually born) the mean proportion of male to female births,\nduring the whole period of the above ten years, was as 102.8 to 100;\nwhilst in N. Wales (where the average annual births are 12,873) it was\nas high as 106.2 to 100. Taking a still smaller district, viz.,\nRutlandshire (where the annual births average only 739), in 1864 the\nmale births were as 114.6, and in 1862 as only 97.0 to 100; but even\nin this small district the average of the 7385 births during the whole\nten years, was as 104.5 to 100: that is in the same ratio as\nthroughout England.* The proportions are sometimes slightly\ndisturbed by unknown causes; thus Prof. Faye states \"that in some\ndistricts of Norway there has been during a decennial period a\nsteady deficiency of boys, whilst in others the opposite condition has\nexisted.\" In France during forty-four years the male to the female\nbirths have been as 106.2 to 100; but during this period it has\noccurred five times in one department, and six times in another,\nthat the female births have exceeded the males. In Russia the\naverage proportion is as high as 108.9, and in Philadelphia in the\nUnited States as 110.5 to 100.*(2) The average for Europe, deduced\nby Bickes from about seventy million births, is 106 males to 100\nfemales. On the other hand, with white children born at the Cape of\nGood Hope, the proportion of males is so low as to fluctuate during\nsuccessive years between 90 and 99 males for every 100 females. It\nis a singular fact that with Jews the proportion of male births is\ndecidedly larger than with Christians: thus in Prussia the\nproportion is as 113, in Breslau as 114, and in Livonia as 120 to 100;\nthe Christian births in these countries being the same as usual, for\ninstance, in Livonia as 104 to 100.*(3)\n * Twenty-ninth Annual Report of the Registrar-General for 1866. In\nthis report (p. xii.) a special decennial table is given.\n *(2) For Norway and Russia, see abstract of Prof. Faye's researches,\nin British and Foreign Medico-Chirurg. Review, April, 1867, pp. 343,\n345. For France, the Annuaire pour l'An 1867, p. 213. For\nPhiladelphia, Dr. Stockton-Hough, Social Science Assoc., 1874. For the\nCape of Good Hope, Quetelet as quoted by Dr. H. H. Zouteveen, in the\nDutch translation of this work (vol. i., p. 417), where much\ninformation is given on the proportion of the sexes.\n *(3) In regard to the Jews, see M. Thury, La Loi de Production des\nSexes, 1863, p. 25.\n Prof. Faye remarks that \"a still greater preponderance of males\nwould be met with, if death struck both sexes in equal proportion in\nthe womb and during birth. But the fact is, that for every 100\nstill-born females, we have in several countries from 134.6 to 144.9\nstillborn males. During the first four or five years of life, also,\nmore male children die than females, for example in England, during\nthe first year, 126 boys die for every 100 girls- a proportion which\nin France is still more unfavourable.\"* Dr. Stockton-Hough accounts\nfor these facts in part by the more frequent defective development\nof males than of females. We have before seen that the male sex is\nmore variable in structure than the female; and variations in\nimportant organs would generally be injurious. But the size of the\nbody, and especially of the head, being greater in male than female\ninfants is another cause: for the males are thus more liable to be\ninjured during parturition. Consequently the still-born males are more\nnumerous; and, as a highly competent judge, Dr. Crichton Browne,*(2)\nbelieves, male infants often suffer in health for some years after\nbirth. Owing to this excess in the death-rate of male children, both\nat birth and for some time subsequently, and owing to the exposure\nof grown men to various dangers, and to their tendency to emigrate,\nthe females in all old-settled countries, where statistical records\nhave been kept,*(3) are found to preponderate considerably over the\nmales.\n * British and Foreign Medico-Chirurg. Review, April, 1867, p. 343.\nDr. Stark also remarks (Tenth Annual Reports of Births, Deaths, &c.,\nin Scotland, 1867, p. xxviii.) that \"These examples may suffice to\nshow that, at almost every stage of life, the males in Scotland have a\ngreater liability to death and a higher death-rate than the females.\nThe fact, however, of this peculiarity being most strongly developed\nat that infantile period of life when the dress, food, and general\ntreatment of both sexes are alike, seems to prove that the higher male\ndeath-rate is an impressed, natural, and constitutional peculiarity\ndue to sex alone.\"\n *(2) West Riding Lunatic Asylum Reports, vol. i., 1871, p. 8. Sir J.\nSimpson has proved that the head of the male infant exceeds that of\nthe female by 3/8ths of an inch in circumference, and by 1/8th in\ntransverse diameter. Quetelet has shown that woman is born smaller\nthan man; see Dr. Duncan, Fecundity, Fertility, and Sterility, 1871,\np. 382.\n *(3) With the savage Guaranys of Paraguay, according to the accurate\nAzara (Voyages dans l'Amerique merid., tom. ii., 1809, pp. 60, 179),\nthe women are to the men in the proportion of 14 to 13.\n It seems at first sight a mysterious fact that in different nations,\nunder different conditions and climates, in Naples, Prussia,\nWestphalia, Holland, France, England and the United States, the excess\nof male over female births is less when they are illegitimate than\nwhen legitimate.* This has been explained by different writers in many\ndifferent ways, as from the mothers being generally young, from the\nlarge proportion of first pregnancies, &c. But we have seen that\nmale infants, from the large size of their heads, suffer more than\nfemale infants during parturition; and as the mothers of\nillegitimate children must be more liable than other women to\nundergo bad labours, from various causes, such as attempts at\nconcealment by tight lacing, hard work, distress of mind, &c., their\nmale infants would proportionably suffer. And this probably is the\nmost efficient of all the causes of the proportion of males to females\nborn alive being less amongst illegitimate children than amongst the\nlegitimate. With most animals the greater size of the adult male\nthan of the female, is due to the stronger males having conquered\nthe weaker in their struggles for the possession of the females, and\nno doubt it is owing to this fact that the two sexes of at least\nsome animals differ in size at birth. Thus we have the curious fact\nthat we may attribute the more frequent deaths of male than female\ninfants, especially amongst the illegitimate, at least in part to\nsexual selection.\n * Babbage, Edinburgh Journal of Science, 1829, vol. i., p. 88;\nalso p. 90, on still-born children. On illegitimate children in\nEngland, see Report of Registrar-General for 1866, p. xv.\n It has often been supposed that the relative age of the two\nparents determine the sex of the offspring; and Prof. Leuckart* has\nadvanced what he considers sufficient evidence, with respect to man\nand certain domesticated animals, that this is one important though\nnot the sole factor in the result. So again the period of impregnation\nrelatively to the state of the female has been thought by some to be\nthe efficient cause; but recent observations discountenance this\nbelief. According to Dr. Stockton-Hough,*(2) the season of the year,\nthe poverty or wealth of the parents, residence in the country or in\ncities, the crossing of foreign immigrants, &c., all influence the\nproportion of the sexes. With mankind, polygamy has also been supposed\nto lead to the birth of a greater proportion of female infants; but\nDr. J. Campbell*(3) carefully attended to this subject in the harems\nof Siam, and concludes that the proportion of male to female births is\nthe same as from monogamous unions. Hardly any animal has been\nrendered so highly polygamous as the English race-horse, and we\nshall immediately see that his male and female offspring are almost\nexactly equal in number. I will now give the facts which I have\ncollected with respect to the proportional numbers of the sexes of\nvarious animals; and will then briefly discuss how far selection has\ncome into play in determining the result.\n * Leuckart, in Wagner's Handworterbuch der Phys., B. iv., 1853, s.\n774.\n *(2) Social Science Association of Philadelphia, 1874.\n *(3) Anthropological Review, April, 1870, p. cviii.\n Horses.- Mr. Tegetmeier has been so kind as to tabulate for me\nfrom the Racing Calendar the births of race-horses during a period\nof twenty-one years, viz., from 1846 to 1867; 1849 being omitted, as\nno returns were that year published. The total births were 25,560,*\nconsisting of 12,763 males and 12,797 females, or in the proportion of\n99.7 males to 100 females. As these numbers are tolerably large, and\nas they are drawn from all parts of England, during several years,\nwe may with much confidence conclude that with the domestic horse,\nor at least with the race-horse, the two sexes are produced in\nalmost equal numbers. The fluctuations in the proportions during\nsuccessive years are closely like those which occur with mankind, when\na small and thinly-populated area is considered; thus in 1856 the male\nhorses were as 107.1, and in 1867 as only 92.6 to 100 females. In\nthe tabulated returns the proportions vary in cycles, for the males\nexceeded the females during six successive years; and the females\nexceeded the males during two periods each of four years; this,\nhowever, may be accidental; at least I can detect nothing of the\nkind with man in the decennial table in the Registrar's Report for\n1866.\n * During eleven years a record was kept of the number of mares which\nproved barren or prematurely slipped their foals; and it deserves\nnotice, as shewing how infertile these highly-nurtured and rather\nclosely-interbred animals have become, that not far from one-third\nof the mares failed to produce living foals. Thus during 1866, 809\nmale colts and 816 female colts were born, and 743 mares failed to\nproduce offspring. During 1867, 836 males and 902 females were born,\nand 794 mares failed.\n Dogs.- During a period of twelve years, from 1857 to 1868, the\nbirths of a large number of greyhounds, throughout England, were\nsent to the Field newspaper; and I am again indebted to Mr. Tegetmeier\nfor carefully tabulating the results. The recorded births were 6878,\nconsisting of 3605 males and 3273 females, that is, in the\nproportion of 110.1 males to 100 females. The greatest fluctuations\noccurred in 1864, when the proportion was as 95.3 males, and in\n1867, as 116.3 males to 100 females. The above average proportion of\n110.1 to 100 is probably nearly correct in the case of the\ngreyhound, but whether it would hold with other domesticated breeds is\nin some degree doubtful. Mr. Cupples has enquired from several great\nbreeders of dogs, and finds that all without exception believe that\nfemales are produced in excess; but he suggests that this belief may\nhave arisen from females being less valued, and from the consequent\ndisappointment producing a stronger impression on the mind.\n Sheep.- The sexes of sheep are not ascertained by agriculturists\nuntil several months after birth, at the period when the males are\ncastrated; so that the following returns do not give the proportions\nat birth. Moreover, I find that several great breeders in Scotland,\nwho annually raise some thousand sheep, are firmly convinced that a\nlarger proportion of males than of females die during the first year\nor two. Therefore the proportion of males would be somewhat larger\nat birth than at the age of castration. This is a remarkable\ncoincidence with what, as we have seen, occurs with mankind, and\nboth cases probably depend on the same cause. I have received\nreturns from four gentlemen in England who have bred lowland sheep,\nchiefly Leicesters, during the last ten to sixteen years; they\namount altogether to 8965 births, consisting of 4407 males and 4558\nfemales; that is in the proportion of 96.7 males to 100 females.\nWith respect to Cheviot and black-faced sheep bred in Scotland, I have\nreceived returns from six breeders, two of them on a large scale,\nchiefly for the years 1867-1869, but some of the returns extend back\nto 1862. The total number recorded amounts to 50,685, consisting of\n25,071 males and 25,614 females or in the proportion of 97.9 males\nto 100 females. If we take the English and Scotch returns together,\nthe total number amounts to 59,650, consisting of 29,478 males and\n30,172 females, or as 97.7 to 100. So that with sheep at the age of\ncastration the females are certainly in excess of the males, but\nprobably this would not hold good at birth.*\n *I am much indebted to Mr. Cupples for having procured for me the\nabove returns from Scotland, as well as some of the following\nreturns on cattle. Mr. R. Elliot, of Laighwood, first called my\nattention to the premature deaths of the males,- a statement\nsubsequently confirmed by Mr. Aitchison and others. To this latter\ngentleman, and to Mr. Payan, I owe my thanks for large returns as to\nsheep.\n Of Cattle I have received returns from nine gentlemen of 982 births,\ntoo few to be trusted; these consisted of 477 bull-calves and 505\ncow-calves; i.e., in the proportion of 94.4 males to 100 females.\nThe Rev. W. D. Fox informs me that in 1867 out of 34 calves born on\na farm in Derbyshire only one was a bull. Mr. Harrison Weir has\nenquired from several breeders of Pigs, and most of them estimate\nthe male to the female births as about 7 to 6. This same gentleman has\nbred rabbits for many years, and has noticed that a far greater number\nof bucks are produced than does. But estimations are of little value.\n Of Mammalia in a state of nature I have been able to learn very\nlittle. In regard to the common rat, I have received conflicting\nstatements. Mr. R. Elliot, of Laighwood, informs me that a rat-catcher\nassured him that he had always found the males in great excess, even\nwith the young in the nest. In consequence of this, Mr. Elliot himself\nsubsequently examined some hundred old ones, and found the statement\ntrue. Mr. F. Buckland has bred a large number of white rats, and he\nalso believes that the males greatly exceed the females. In regard\nto moles, it is said that \"the males are much more numerous than the\nfemales\":* and as the catching of these animals is a special\noccupation, the statement may perhaps be trusted. Sir A. Smith, in\ndescribing an antelope of S. Africa*(2) (Kobus ellipsiprymnus),\nremarks, that in the herds of this and other species, the males are\nfew in number compared with the females: the natives believe that they\nare born in this proportion; others believe that the younger males are\nexpelled from the herds, and Sir A. Smith says, that though he has\nhimself never seen herds consisting of young males alone, others\naffirm that this does occur. It appears probable that the young when\nexpelled from the herd, would often fall a prey to the many beasts\nof prey of the country.\n * Bell, History of British Quadrupeds, p. 100.\n *(2) Illustrations of the Zoology of S. Africa, 1849, pl. 29.\n BIRDS.\n With respect to the Fowl, I have received only one account,\nnamely, that out of 1001 chickens of a highly-bred stock of Cochins,\nreared during eight years by Mr. Stretch, 487 proved males and 514\nfemales; i.e., as 94.7 to 100. In regard to domestic pigeons there\nis good evidence either that the males are produced in excess, or that\nthey live longer; for these birds invariably pair, and single males,\nas Mr. Tegetmeier informs me, can always be purchased cheaper than\nfemales. Usually the two birds reared from the two eggs laid in the\nsame nest are a male and a female; but Mr. Harrison Weir, who has been\nso large a breeder, says that he has often bred two cocks from the\nsame nest, and seldom two hens; moreover, the hen is generally the\nweaker of the two, and more liable to perish.\n With respect to birds in a state of nature, Mr. Gould and others*\nare convinced that the males are generally the more numerous; and as\nthe young males of many species resemble the females, the latter would\nnaturally appear to be the more numerous. Large numbers of pheasants\nare reared by Mr. Baker of Leadenhall from eggs laid by wild birds,\nand he informs Mr. Jenner Weir that four or five males to one female\nare generally produced. An experienced observer remarks,*(2) that in\nScandinavia the broods of the capercailzie and black-cock contain more\nmales than females; and that with the Dal-ripa (a kind of ptarmigan)\nmore males than females attend the leks or places of courtship; but\nthis latter circumstance is accounted for by some observers by a\ngreater number of hen birds being killed by vermin. From various facts\ngiven by White of Selborne,*(3) it seems clear that the males of the\npartridge must be in considerable excess in the south of England;\nand I have been assured that this is the case in Scotland. Mr. Weir on\nenquiring from the dealers, who receive at certain seasons large\nnumbers of ruffs (Machetes pugnax), was told that the males are much\nthe more numerous. This same naturalist has also enquired for me\nfrom the birdcatchers, who annually catch an astonishing number of\nvarious small species alive for the London market, and he was\nunhesitatingly answered by an old and trustworthy man, that with the\nchaffinch the males are in large excess: he thought as high as 2 males\nto 1 female, or at least as high as 5 to 3.*(4) The males of the\nblackbird, he likewise maintained, were by far the more numerous,\nwhether caught by traps or by netting at night. These statements may\napparently be trusted, because this same man said that the sexes are\nabout equal with the lark, the twite (Linaria montana), and goldfinch.\nOn the other hand, he is certain that with the common linnet, the\nfemales preponderate greatly, but unequally during different years;\nduring some years he has found the females to the males as four to\none. It should, however, be borne in mind, that the chief season for\ncatching birds does not begin till September, so that with some\nspecies partial migrations may have begun, and the flocks at this\nperiod often consist of hens alone. Mr. Salvin paid particular\nattention to the sexes of the humming-birds in Central America, and is\nconvinced that with most of the species the males are in excess;\nthus one year he procured 204 specimens belonging to ten species,\nand these consisted of 166 males and of only 38 females. With two\nother species the females were in excess: but the proportions\napparently vary either during different seasons or in different\nlocalities; for on one occasion the males of Campylopterus\nhemileucurus were to the females as 5 to 2, and on another\noccasion*(5) in exactly the reversed ratio. As bearing on this\nlatter point, I may add, that Mr. Powys found in Corfu and Epirus\nthe sexes of the chaffinch keeping apart, and \"the females by far\nthe most numerous\"; whilst in Palestine Mr. Tristram found \"the male\nflocks appearing greatly to exceed the female in number.\"*(6) So again\nwith the Quiscalus major, Mr. G. Taylor says, that in Florida there\nwere \"very few females in proportion to the males,\"*(7) whilst in\nHonduras the proportion was the other way, the species there having\nthe character of a polygamist.\n * Brehm (Illustriertes Thierleben, B. iv., s. 990) comes to the same\nconclusion.\n *(2) On the authority of L. Lloyd, Game Birds of Sweden, 1867, pp.\n12, 132.\n *(3) Nat. Hist. of Selborne, letter xxix., ed. of 1825, vol. i.,\np. 139.\n *(4) Mr. Jenner Weir received similar information, on making\nenquiries during the following year. To shew the number of living\nchaffinches caught, I may mention that in 1869 there was a match\nbetween two experts, and one man caught in a day 62, and another 40,\nmale chaffinches. The greatest number ever caught by one man in a\nsingle day was 70.\n *(5) Ibis, vol. ii. p. 260, as quoted in Gould's Trochilidae,\n1861, p. 52. For the foregoing proportions, I am indebted to Mr.\nSalvin for a table of his results.\n *(6) Ibis, 1860, p. 137; and 1867, p. 369.\n *(7) Ibis, 1862, p. 187.\n FISH.\n With fish the proportional numbers of the sexes can be ascertained\nonly by catching them in the adult or nearly adult state; and there\nare many difficulties in arriving at any just conclusion.* Infertile\nfemales might readily be mistaken for males, as Dr. Gunther has\nremarked to me in regard to trout. With some species the males are\nbelieved to die soon after fertilising the ova. With many species\nthe males are of much smaller size than the females, so that a large\nnumber of males would escape from the same net by which the females\nwere caught. M. Carbonnier,*(2) who has especially attended to the\nnatural history of the pike (Esox lucius), states that many males,\nowing to their small size, are devoured by the larger females; and\nhe believes that the males of almost all fish are exposed from this\nsame cause to greater danger than the females. Nevertheless, in the\nfew cases in which the proportional numbers have been actually\nobserved, the males appear to be largely in excess. Thus Mr. R. Buist,\nthe superintendent of the Stormontfield experiments, says that in\n1865, out of 70 salmon first landed for the purpose of obtaining the\nova, upwards of 60 were males. In 1867 he again \"calls attention to\nthe vast disproportion of the males to the females. We had at the\noutset at least ten males to one female.\" Afterwards females\nsufficient for obtaining ova were procured. He adds, \"from the great\nproportion of the males, they are constantly fighting and tearing each\nother on the spawning-beds.\"*(3) This disproportion, no doubt, can\nbe accounted for in part, but whether wholly is doubtful, by the males\nascending the rivers before the females. Mr. F. Buckland remarks in\nregard to trout, that \"it is a curious fact that the males\npreponderate very largely in number over the females. It invariably\nhappens that when the first rush of fish is made to the net, there\nwill be at least seven or eight males to one female found captive. I\ncannot quite account for this; either the males are more numerous than\nthe females, or the latter seek safety by concealment rather than\nflight.\" He then adds, that by carefully searching the banks\nsufficient females for obtaining ova can be found.*(4) Mr. H. Lee\ninforms me that out of 212 trout taken for this purpose in Lord\nPortsmouth's park, 150 were males and 62 females.\n * Leuckart quotes Bloch (Wagner, Handworterbuch der Phys., B. iv.,\n1853, s. 775), that with fish there are twice as many males as\nfemales.\n *(2) Quoted in the Farmer, March 18, 1869, p. 369.\n *(3) The Stormontfield Piscicultural Experiments, 1866, p. 23. The\nField newspaper, June 29, 1867.\n *(4) Land and Water, 1868, p. 41.\n The males of the Cyprinidae likewise seem to be in excess; but\nseveral members of this family, viz., the carp, tench, bream and\nminnow, appear regularly to follow the practice, rare in the animal\nkingdom, of polyandry; for the female whilst spawning is always\nattended by two males, one on each side, and in the case of the\nbream by three or four males. This fact is so well known, that it is\nalways recommended to stock a pond with two male tenches to one\nfemale, or at least with three males to two females. With the\nminnow, an excellent observer states, that on the spawning-beds the\nmales are ten times as numerous as the females; when a female comes\namongst the males, \"she is immediately pressed closely by a male on\neach side; and when they have been in that situation for a time, are\nsuperseded by other two males.\"*\n * Yarrell, Hist. British Fishes, vol. i., 1826, p. 307; on the\nCyprinus carpio, p. 331; on the Tinca vulgaris, p. 331; on the Abramis\nbrama, p. 336. See, for the minnow (Leuciscus phoxinus), Loudon's\nMagazine of Natural History, vol. v., 1832, p. 682.\n INSECTS.\n In this great class, the Lepidoptera almost alone affords means\nfor judging of the proportional numbers of the sexes; for they have\nbeen collected with special care by many good observers, and have been\nlargely bred from the egg or caterpillar state. I had hoped that\nsome breeders of silk-moths might have kept an exact record, but after\nwriting to France and Italy, and consulting various treatises, I\ncannot find that this has ever been done. The general opinion\nappears to be that the sexes are nearly equal, but in Italy, as I hear\nfrom Professor Canestrini, many breeders are convinced that the\nfemales are produced in excess. This same naturalist, however, informs\nme, that in the two yearly broods of the ailanthus silk-moth (Bombyx\ncynthia), the males greatly preponderate in the first, whilst in the\nsecond the two sexes are nearly equal, or the females rather in\nexcess.\n In regard to butterflies in a state of nature, several observers\nhave been much struck by the apparently enormous preponderance of\nthe males.* Thus Mr. Bates,*(2) in speaking of several species,\nabout a hundred in number, which inhabit the upper Amazons, says\nthat the males are much more numerous than the females, even in the\nproportion of a hundred to one. In North America, Edwards, who had\ngreat experience, estimates in the genus Papilio the males to the\nfemales as four to one; and Mr. Walsh, who informs me of this\nstatement, says that with P. turnus this is certainly the case. In\nSouth Africa, Mr. R. Trimen found the males in excess in 19\nspecies;*(3) and in one of these, which swarms in open places, he\nestimated the number of males as fifty to one female. With another\nspecies, in which the males are numerous in certain localities, he\ncollected only five females during seven years. In the island of\nBourbon, M. Maillard states that the males of one species of Papilio\nare twenty times as numerous as the females.*(4) Mr. Trimen informs me\nthat as far as he has himself seen, or heard from others, it is rare\nfor the females of any butterfly to exceed the males in number; but\nthree South African species perhaps offer an exception. Mr.\nWallace*(5) states that the females of Ornithoptera croesus, in the\nMalay Archipelago, are more common and more easily caught than the\nmales; but this is a rare butterfly. I may here add, that in\nHyperythra, a genus of moths, Guenee says, that from four to five\nfemales are sent in collections from India for one male.\n * Leuckart quotes Meinecke (Wagner, Handworterbuch der Phys., B.\niv., 1853, s. 775) that the males of butterflies are three or four\ntimes as numerous as the females.\n *(2) The Naturalist on the Amazons, vol. ii., 1863, pp. 228, 347.\n *(3) Four of these cases are given by Mr. Trimen in his\nRhopalocera Africae Australis.\n *(4) Quoted by Trimen, Transactions of the Ent. Society, vol. v.,\npart iv., 1866, p. 330.\n *(5) Transactions, Linnean Society, vol. xxv., p. 37.\n When this subject of the proportional numbers of the sexes of\ninsects was brought before the Entomological Society,* it was\ngenerally admitted that the males of most Lepidoptera, in the adult or\nimago state, are caught in greater numbers than the females: but\nthis fact was attributed by various observers to the more retiring\nhabits of the females, and to the males emerging earlier from the\ncocoon. This latter circumstance is well known to occur with most\nLepidoptera, as well as with other insects. So that, as M. Personnat\nremarks, the males of the domesticated Bombyx yamamai., are useless at\nthe beginning of the season, and the females at the end, from the want\nof mates.*(2) I cannot, however, persuade myself that these causes\nsuffice to explain the great excess of males, in the above cases of\ncertain butterflies which are extremely common in their native\ncountries. Mr. Stainton, who has paid very close attention during many\nyears to the smaller moths, informs me that when he collected them\nin the imago state, he thought that the males were ten times as\nnumerous as the females, but that since he has reared them on a\nlarge scale from the caterpillar state, he is convinced that the\nfemales are the more numerous. Several entomologists concur in this\nview. Mr. Doubleday, however, and some others, take an opposite\nview, and are convinced that they have reared from the eggs and\ncaterpillars a larger proportion of males than of females.\n * Proceedings, Entomological Society, Feb. 17, 1868.\n *(2) Quoted by Dr. Wallace in Proceedings, Entomological Society,\n3rd series, vol. v., 1867, p. 487.\n Besides the more active habits of the males, their earlier emergence\nfrom the cocoon, and in some cases their frequenting more open\nstations, other causes may be assigned for an apparent or real\ndifference in the proportional numbers of the sexes of Lepidoptera,\nwhen captured in the imago state, and when reared from the egg or\ncaterpillar state. I hear from Professor Canestrini, that it is\nbelieved by many breeders in Italy, that the female caterpillar of the\nsilk-moth suffers more from the recent disease than the male; and\nDr. Staudinger informs me that in rearing Lepidoptera more females die\nin the cocoon than males. With many species the female caterpillar\nis larger than the male, and a collector would naturally choose the\nfinest specimens, and thus unintentionally collect a larger number\nof females. Three collectors have told me that this was their\npractice; but Dr. Wallace is sure that most collectors take all the\nspecimens which they can find of the rarer kinds, which alone are\nworth the trouble of rearing. Birds when surrounded by caterpillars\nwould probably devour the largest; and Professor Canestrini informs me\nthat in Italy some breeders believe, though on insufficient\nevidence, that in the first broods of the ailanthus silkmoth, the\nwasps destroy a larger number of the female than of the male\ncaterpillars. Dr. Wallace further remarks that female caterpillars,\nfrom being larger than the males, require more time for their\ndevelopment, and consume more food and moisture: and thus they would\nbe exposed during a longer time to danger from ichneumons, birds, &c.,\nand in times of scarcity would perish in greater numbers. Hence it\nappears quite possible that in a state of nature, fewer female\nLepidoptera may reach maturity than males; and for our special\nobject we are concerned with their relative numbers at maturity,\nwhen the sexes are ready to propagate their kind.\n The manner in which the males of certain moths congregate in\nextraordinary numbers round a single female, apparently indicates a\ngreat excess of males, though this fact may perhaps be accounted for\nby the earlier emergence of the males from their cocoons. Mr. Stainton\ninforms me that from twelve to twenty males, may often be seen\ncongregated round a female Elachista rufocinerea. It is well known\nthat if a virgin Lasiocampa quercus or Saturnia carpini be exposed\nin a cage, vast numbers of males collect round her, and if confined in\na room will even come down the chimney to her. Mr. Doubleday\nbelieves that he has seen from fifty to a hundred males of both\nthese species attracted in the course of a single day by a female in\nconfinement. In the Isle of Wight Mr. Trimen exposed a box in which\na female of the Lasiocampa had been confined on the previous day,\nand five males soon endeavored to gain admittance. In Australia, Mr.\nVerreaux, having placed the female of a small Bombyx in a box in his\npocket, was followed by a crowd of males, so that about 200 entered\nthe house with him.*\n * Blanchard, Metamorphoses, Moeurs des Insectes, 1868, pp. 225-226.\n Mr. Doubleday has called my attention to M. Staudinger's* list of\nLepidoptera, which gives the prices of the males and females of 300\nspecies or well-marked varieties of butterflies (Rhopalocera). The\nprices for both sexes of the very common species are of course the\nsame; but in 114 of the rarer species they differ; the males being\nin all cases, excepting one, the cheaper. On an average of the\nprices of the 113 species, the price of the male to that of the female\nis as 100 to 149; and this apparently indicates that inversely the\nmales exceed the females in the same proportion. About 2000 species or\nvarieties of moths (Heterocera) are catalogued, those with wingless\nfemales being here excluded on account of the difference in habits\nbetween the two sexes: of these 2000 species, 141 differ in price\naccording to sex, the males of 130 being cheaper, and those of only 11\nbeing dearer than the females. The average price of the males of the\n130 species, to that of the females, is as 100 to 143. With respect to\nthe butterflies in this priced list, Mr. Doubleday thinks (and no\nman in England has had more experience), that there is nothing in\nthe habits of the species which can account for the difference in\nthe prices of the two sexes, and that it can be accounted for only\nby an excess in the number of the males. But I am bound to add that\nDr. Staudinger informs me, that he is himself of a different\nopinion. He thinks that the less active habits of the females and\nthe earlier emergence of the males will account for his collectors\nsecuring a larger number of males than of females, and consequently\nfor the lower prices of the former. With respect to specimens reared\nfrom the caterpillar-state, Dr. Staudinger believes, as previously\nstated, that a greater number of females than of males die whilst\nconfined to the cocoons. He adds that with certain species one sex\nseems to preponderate over the other during certain years.\n * Lepidopteren-Doubletten Liste, Berlin, No. x., 1866.\n Of direct observations on the sexes of Lepidoptera, reared either\nfrom eggs or caterpillars, I have received only the few following\ncases:*\n * See following table.\n So that in these eight lots of cocoons and eggs, males were produced\nin excess. Taken together the proportion of males is as 122.7 to 100\nfemales. But the numbers are hardly large enough to be trustworthy.\n On the whole, from these various sources of evidence, all pointing\nin the same direction, I infer that with most species of\nLepidoptera, the mature males generally exceed the females in\nnumber, whatever the proportions may be at their first emergence\nfrom the egg.\n Males Females\n The Rev. J. Hellins* of Exeter reared, during\n 1868, imagos of 73 species, which\n consisted of 153 137\n Mr. Albert Jones of Eltham reared, during\n 1868, imagos of 9 species, which\n consisted of 159 126\n During 1869 he reared imagoes from 4 species\n consisting of 114 112\n Mr. Buckler of Emsworth, Hants, during 1869,\n reared imagos from 74 species,\n consisting of 180 169\n Dr. Wallace of Colchester reared from one\n brood of Bombyx cynthia 52 48\n Dr. Wallace raised, from cocoons of Bombyx\n pernyi sent from China, during 1869 224 123\n Dr. Wallace raised, during 1868 and 1869, from\n two lots of cocoons of Bombyx yamamai 52 46\n Total 934 761\n * This naturalist has been so kind as to send me some results from\nformer years, in which the females seemed to preponderate; but so many\nof the figures were estimates, that I found it impossible to\ntabulate them\n With reference to the other orders of insects, I have been able to\ncollect very little reliable information. With the stag-beetle\n(Lucanus cervus) \"the males appear to be much more numerous than the\nfemales\"; but when, as Cornelius remarked during 1867, an unusal\nnumber of these beetles appeared in one part of Germany, the females\nappeared to exceed the males as six to one. With one of the\nElateridae, the males are said to be much more numerous than the\nfemales, and \"two or three are often found united with one female;* so\nthat here polyandry seems to prevail.\" With Siagonium (Staphylinidae),\nin which the males are furnished with horns, \"the females are far more\nnumerous than the opposite sex.\" Mr. Janson stated at the\nEntomological Society that the females of the bark feeding Tomicus\nvillosus are so common as to be a plague, whilst the males are so rare\nas to be hardly known.\n * Gunther's Record of Zoological Literature, 1867, p. 260. On the\nexcess of female Lucanus, ibid, p. 250. On the males of Lucanus in\nEngland, Westwood, Modern Classification of Insects, vol. i., p.\n187. On the Siagonium, ibid., p. 172.\n It is hardly worthwhile saying anything about the proportion of\nthe sexes in certain species and even groups of insects, for the males\nare unknown or very rare, and the females are parthenogenetic, that\nis, fertile without sexual union; examples of this are afforded by\nseveral of the Cynipidae.* In all the gall-making Cynipidae known to\nMr. Walsh, the females are four or five times as numerous as the\nmales; and so it is, as he informs me, with the gall-making\nCecidomyiidae (Diptera). With some common species of saw-flies\n(Tenthredinae) Mr. F. Smith has reared hundreds of specimens from\nlarvae of all sizes, but has never reared a single male; on the\nother hand, Curtis says,*(2) that with certain species (Athalia), bred\nby him, the males were to the females as six to one; whilst exactly\nthe reverse occurred with the mature insects of the same species\ncaught in the fields. In the family of bees, Hermann Muller,*(3)\ncollected a large number of specimens of many species, and reared\nothers from the cocoons, and counted the sexes. He found that the\nmales of some species greatly exceeded the females in number; in\nothers the reverse occurred; and in others the two sexes were nearly\nequal. But as in most cases the males emerge from the cocoons before\nthe females, they are at the commencement of the breeding-season\npractically in excess. Muller also observed that the relative number\nof the two sexes in some species differed much in different\nlocalities. But as H. Muller has himself remarked to me, these remarks\nmust be received with some caution, as one sex might more easily\nescape observation than the other. Thus his brother Fritz Muller has\nnoticed in Brazil that the two sexes of the same species of bee\nsometimes frequent different kinds of flowers. With respect to the\nOrthoptera, I know hardly anything about the relative number of the\nsexes: Korte,*(4) however, says that out of 500 locusts which he\nexamined, the males were to the females as five to six. With the\nNeuroptera, Mr. Walsh states that in many, but by no means in all\nthe species of the odonatous group, there is a great overplus of\nmales: in the genus Hetaerina, also, the males are generally at\nleast four times as numerous as the females. In certain species in the\ngenus Gomphus the males are equally in excess, whilst in two other\nspecies, the females the are twice or thrice as numerous as the males.\nIn some European species of Psocus thousands of females may be\ncollected without a single male, whilst with other species of the same\ngenus both sexes are common.*(5) In England, Mr. MacLachlan has\ncaptured hundreds of the female Apatania muliebris, but has never seen\nthe male; and of Boreus hyemalis only four or five males have been\nseen here.*(6) With most of these species (excepting the Tenthredinae)\nthere is at present no evidence that the females are subject to\nparthenogenesis; and thus we see how ignorant we are of the causes\nof the apparent discrepancy in the proportion of the two sexes.\n * Walsh in the American Entomologist, vol. i., 1869, p. 103. F.\nSmith, Record of Zoological Lit, 1867, p. 328.\n *(2) Farm Insects, pp. 45-46.\n *(3) \"Anwendung der Darwin'schen Lehre,\" Verh. d. n. Jahrg., xxiv.\n *(4) Die Strich. Zug oder Wanderheuschrecke, 1828, p. 20.\n *(5) \"Observations on N. American Neuroptera,\" by H. Hagen and B. D.\nWalsh, Proceedings, Ent. Soc. Philadelphia, Oct., 1863, pp. 168,\n223, 239.\n *(6) Proceedings, Ent. Soc. London, Feb. 17, 1868.\n In the other classes of the Articulata I have been able to collect\nstill less information. With spiders, Mr. Blackwall, who has carefully\nattended to this class during many years, writes to me that the\nmales from their more erratic habits are more commonly seen, and\ntherefore appear more numerous. This is actually the case with a few\nspecies; but he mentions several species in six genera, in which the\nfemales appear to be much more numerous than the males.* The small\nsize of the males in comparison with the females (a peculiarity\nwhich is sometimes carried to an extreme degree), and their widely\ndifferent appearance, may account in some instances for their rarity\nin collections.*(2)\n8888\n * Another great authority with respect to this class, Prof.\nThorell of Upsala (On European Spiders, 1869-70, part i., p. 205),\nspeaks as if female spiders were generally commoner than the males.\n *(2) See, on this subject, Mr. O. P. Cambridge, as quoted in\nQuarterly Journal of Science, 1868, page 429.\n Some of the lower crustaceans are able to propagate their kind\nsexually, and this will account for the extreme rarity of the males;\nthus von Siebold* carefully examined no less than 13,000 specimens\nof Apus from twenty-one localities, and amongst these he found only\n319 males. With some other forms (as Tanais and Cypris), as Fritz\nMuller informs me, there is reason to believe that the males are\nmuch shorter-lived than the females; and this would explain their\nscarcity, supposing the two sexes to be at first equal in number. On\nthe other hand, Muller has invariably taken far more males than\nfemales of the Diastylidae and of Cypridina on the shores of Brazil:\nthus with a species in the latter genus, 63 specimens caught the\nsame day included 57 males; but he suggests that this preponderance\nmay be due to some unknown difference in the habits of the two\nsexes. With one of the higher Brazilian crabs, namely a Gelasimus,\nFritz Muller found the males to be more numerous than the females.\nAccording to the large experience of Mr. C. Spence Bate, the reverse\nseems to be the case with six common British crabs, the names of which\nhe has given me.\n * Beitrage zur Parthenogenesis, p. 174.\n The proportion of the sexes in relation to natural selection.\n There is reason to suspect that in some cases man has by\nselection6 indirectly influenced his own sex-producing powers. Certain\nwomen tend to produce during their whole lives more children of one\nsex than of the other: and the same holds good of many animals, for\ninstance, cows and ho6rses; thus Mr. Wright of Yeldersley House\ninforms me that one of his Arab mares, though put seven times to\ndifferent horses, produced seven fillies. Though I have very little\nevidence on this head, analogy would lead to the belief, that the\ntendency to produce either sex would be inherited like almost every\nother peculiarity, for instance, that of producing twins; and\nconcerning the above tendency a good authority, Mr. J. Downing, has\ncommunicated to me facts which seem to prove that this does occur in\ncertain families of short-horn cattle. Col. Marshall* has recently\nfound on careful examination that the Todas, a hill-tribe of India,\nconsist of 112 males and 84 females of all ages- that is in a ratio of\n133.3 males to 100 females. The Todas, who are polyandrous in their\nmarriages, during former times invariably practised female\ninfanticide; but this practice has now been discontinued for a\nconsiderable period. Of the children born within late years, the males\nare more numerous than the females, in the proportion of 124 to 100.\nColonel Marshall accounts for this fact in the following ingenious\nmanner. \"Let us for the purpose of illustration take three families as\nrepresenting an average of the entire tribe; say that one mother gives\nbirth to six daughters and no sons; a second mother has six sons only,\nwhilst the third mother has three sons and three daughters. The\nfirst mother, following the tribal custom, destroys four daughters and\npreserves two. The second retains her six sons. The third kills two\ndaughters and keeps one, as also her three sons. We have then from the\nthree families, nine sons and three daughters, with which to\ncontinue the breed. But whilst the males belong to families in which\nthe tendency to produce sons is great, the females are of those of a\nconverse inclination. Thus the bias strengthens with each\ngeneration, until, as we find, families grow to have habitually more\nsons than daughters.\"\n * The Todas, 1873, pp. 100, 111, 194, 196.\n That this result would follow from the above form of infanticide\nseems almost certain; that is if we assume that a sex-producing\ntendency is inherited. But as the above numbers are so extremely\nscanty, I have searched for additional evidence, but cannot decide\nwhether what I have found is trustworthy; nevertheless the facts\nare, perhaps, worth giving. The Maories of New Zealand have long\npractised infanticide; and Mr. Fenton* states that he \"has met with\ninstances of women who have destroyed four, six, and even seven\nchildren, mostly females. However, the universal testimony of those\nbest qualified to judge, is conclusive that this custom has for many\nyears been almost extinct. Probably the year 1835 may be named as\nthe period of its ceasing to exist.\" Now amongst the New Zealanders,\nas with the Todas, male births are considerably in excess. Mr.\nFenton remarks (p. 30), \"One fact is certain, although the exact\nperiod of the commencement of this singular condition of the\ndisproportion of the sexes cannot be demonstratively fixed, it is\nquite clear that this course of decrease was in full operation\nduring the years 1830 to 1844, when the non-adult population of 1844\nwas being produced, and has continued with great energy up to the\npresent time.\" The following statements are taken from Mr. Fenton\n(p. 26), but as the numbers are not large, and as the census was not\naccurate, uniform results cannot be expected. It should be borne in\nmind in this and the following cases, that the normal state of every\npopulation is an excess of women, at least in all civilised countries,\nchiefly owing to the greater mortality of the male sex during youth,\nand partly to accidents of all kinds later in life. In 1858, the\nnative population of New Zealand was estimated as consisting of 31,667\nmales and 24,303 females of all ages, that is in the ratio of 130.3\nmales to 100 females. But during this same year, and in certain\nlimited districts, the numbers were ascertained with much care, and\nthe males of all ages were here 753 and the females 616; that is in\nthe ratio of 122.2 males to 100 females. It is more important for us\nthat during this same year of 1858, the non-adult males within the\nsame district were found to be 178, and the non-adult females 142,\nthat is in the ratio of 125.3 to 100. It may be added that in 1844, at\nwhich period female infanticide had only lately ceased, the\nnon-adult males in one district were 281, and the non-adult females\nonly 194, that is in the ratio of 144.8 males to 100 females.\n * Aboriginal Inhabitants of New Zealand (Government Report), 1859,\np. 36.\n In the Sandwich Islands, the males exceed the females in number.\nInfanticide was formerly practised there to a frightful extent, but\nwas by no means confined to female infants, as is shown by Mr. Ellis,*\nand as I have been informed by Bishop Staley and the Rev. Mr. Coan.\nNevertheless, another apparently trustworthy writer, Mr. Jarves,*(2)\nwhose observations apply to the whole archipelago, remarks:-\n\"Numbers of women are to be found, who confess to the murder of from\nthree to six or eight children,\" and he adds, \"females from being\nconsidered less useful than males were more often destroyed.\" From\nwhat is known to occur in other parts of the world, this statement\nis probable; but must be received with much caution. The practice of\ninfanticide ceased about the year 1819, when idolatry was abolished\nand missionaries settled in the islands. A careful census in 1839 of\nthe adult and taxable men and women in the island of Kauai and in\none district of Oahu (Jarves, p. 404), gives 4723 males and 3776\nfemales; that is in the ratio of 125.08 to 100. At the same time the\nnumber of males under fourteen years in Kauai and under eighteen in\nOahu was 1797, and of females of the same ages 1429; and here we\nhave the ratio of 125.75 males to 100 females.\n * Narrative of a Tour through Hawaii, 1826, p. 298.\n *(2) History of the Sandwich Islands, 1843, p. 93.\n In a census of all the islands in 1850,* the males of all ages\namount to 36,272, and the females to 33,128, or as 109.49 to 100.\nThe males under seventeen years amounted to 10,773, and the females\nunder the same age to 9593, or as 112.3 to 100. From the census of\n1872, the proportion of males of all ages (including half-castes) to\nfemales, is as 125.36 to 100. It must be borne in mind that all\nthese returns for the Sandwich Islands give the proportion of living\nmales to living females, and not of the births; and judging from all\ncivilised countries the proportion of males would have been\nconsiderably higher if the numbers had referred to births.*(2)\n * This is given in the Rev. H. T. Cheever's Life in the Sandwich\nIslands, 1851, p. 277.\n *(2) Dr. Coulter, in describing (Journal R. Geograph. Soc., vol. v.,\n1835, p. 67) the state of California about the year 1830, says that\nthe natives reclaimed by the Spanish missionaries, have nearly all\nperished, or are perishing, although well treated, not driven from\ntheir native land, and kept from the use of spirits. He attributes\nthis, in great part, to the undoubted fact that the men greatly exceed\nthe women in number; but he does not know whether this is due to a\nfailure of female offspring, or to more females dying during early\nyouth. The latter alternative, according to all analogy, is very\nimprobable. He adds that \"infanticide, properly so called, is not\ncommon, though very frequent recourse is had to abortion.\" If Dr.\nCoulter is correct about infanticide, this case cannot be advanced\nin support of Colonel Marshall's view. From the rapid decrease of\nthe reclaimed natives, we may suspect that, as in the cases lately\ngiven, their fertility has been diminished from changed habits of\nlife.\n I had hoped to gain some light on this subject from the breeding\nof dogs; inasmuch as most breeds, with the exception, perhaps, of\ngreyhounds, many more female puppies are destroyed than males, just as\nwith the Toda infants. Mr. Cupples assures me that this is usual\nwith Scotch deerhounds. Unfortunately, I know nothing of the\nproportion of the sexes in any breed, excepting greyhounds, and\nthere the male births are to the females as 110.1 to 100. Now from\nenquiries made from many breeders, it seems that the females are in\nsome respects more esteemed, though otherwise troublesome; and it does\nnot appear that the female puppies of the best-bred dogs are\nsystematically destroyed more than the males, though this does\nsometimes take place to a limited extent. Therefore I am unable to\ndecide whether we can, on the above principles, account for the\npreponderance of male births in greyhounds. On the other hand, we have\nseen that with horses, cattle, and sheep, which are too valuable for\nthe young of either sex to be destroyed, if there is any difference,\nthe females are slightly in excess.\n From the several foregoing cases we have some reason to believe that\ninfanticide practised in the manner above explained, tends to make a\nmale-producing race; but I am far from supposing that this practice in\nthe case of man, or some analogous process with other species, has\nbeen the sole determining cause of an excess of males. There may be\nsome unknown law leading to this result in decreasing races, which\nhave already become somewhat infertile. Besides the several causes\npreviously alluded to, the greater facility of parturition amongst\nsavages, and the less consequent injury to their male infants, would\ntend to increase the proportion of live-born males to females. There\ndoes not, however, seem to be any necessary connection between\nsavage life and a marked excess of males; that is if we may judge by\nthe character of the scanty offspring of the lately existing\nTasmanians and of the crossed offspring of the Tahitians now\ninhabiting Norfolk Island.\n As the males and females of many animals differ somewhat in habits\nand are exposed in different degrees to danger, it is probable that in\nmany cases, more of one sex than of the other are habitually\ndestroyed. But as far as I can trace out the complication of causes,\nan indiscriminate though large destruction of either sex would not\ntend to modify the sex-producing power of the species. With strictly\nsocial animals, such as bees or ants, which produce a vast number of\nsterile and fertile females in comparison with the males, and to\nwhom this preponderance is of paramount importance, we can see that\nthose communities would flourish best which contained females having a\nstrong inherited tendency to produce more and more females; and in\nsuch cases an unequal sex-producing tendency would be ultimately\ngained through natural selection. With animals living in herds or\ntroops, in which the males come to the front and defend the herd, as\nwith the bisons of North America and certain baboons, it is\nconceivable that a male-producing tendency might be gained by\nnatural selection; for the individuals of the better defended herds\nwould leave more numerous descendants. In the case of mankind the\nadvantage arising from having a preponderance of men in the tribe is\nsupposed to be one chief cause of the practice of female infanticide.\n In no case, as far as we can see, would an inherited tendency to\nproduce both sexes in equal numbers or to produce one sex in excess,\nbe a direct advantage or disadvantage to certain individuals more than\nto others; for instance, an individual with a tendency to produce more\nmales than females would not succeed better in the battle for life\nthan an individual with an opposite tendency; and therefore a tendency\nof this kind could not be gained through natural selection.\nNevertheless, there are certain animals (for instance, fishes and\ncirripedes) in which two or more males appear to be necessary for\nthe fertilisation of the female; and the males accordingly largely\npreponderate, but it is by no means obvious how this male-producing\ntendency could have been acquired. I formerly thought that when a\ntendency to produce the two sexes in equal numbers was advantageous to\nthe species, it would follow from natural selection, but I now see\nthat the whole problem is so intricate that it is safer to leave its\nsolution for the future.","title":"Part Two - Sexual Selection","type":"page"}