Extra-Sensory Perception: Part III. Explanation and Discussion: Chapter 14. Some General Biological Considerations

This is a chapter from J. B. Rhine's *Extra-Sensory Perception* (1934), the foundational academic text that established experimental parapsychology as a laboratory discipline at Duke University. The chapter covers three loosely connected topics: the possible heritability of ESP ability, its prevalence and distribution across the human population, and an observed "species-level" performance ceiling among Rhine's best subjects. On heritability, Rhine reports that seven of his eight major subjects have relatives with reported psychic experiences, offering this as suggestive (though not statistically proven) evidence that ESP sensitivity may run in families. On prevalence, he argues that negative experimental results are never conclusive due to the demanding conditions ESP requires, and estimates—based on his own graduate students—that perhaps 50% of people may possess measurable ESP ability under ideal circumstances. Most distinctively, the chapter introduces Rhine's observation that his top subjects consistently score between 8 and 11 correct guesses out of 25 trials regardless of individual differences, which he interprets as a possible innate "species ceiling" analogous to the fixed sensory ranges (like hearing or vision) shared across a biological species—a speculative but recurring claim that ESP may be a natural perceptual faculty rather than an anomaly.