This is a scholarly essay in the tradition of late 19th/early 20th-century evolutionary anthropology and comparative religion, arguing that the human concept of soul or spirit arose through rational inference from observable natural phenomena rather than revelation or pure invention. The central claim is that early humans, reasoning from two categories of experience — the apparent separation of mind from body during sleep and dreams, and the cessation of all activity with a person's dying breath — logically deduced that they were dual beings composed of body and an invisible animating principle. The author builds to this by first establishing that rudimentary rational capacities (shame, fear of the uncanny) exist in animals, using anecdotes of dogs reacting to cast-iron replicas and moving bones, to argue there is no sharp cognitive break between animals and early humans. A distinctive move is the author's serious treatment of dream phenomenology among "primitive peoples": because savages experienced dreams as literally real events occurring to a traveling soul, the companion observation that their bodies never moved provided near-conclusive evidence for a separable soul. The text's perspective is explicitly evolutionary-rationalist — it insists that animism and soul-belief were not superstitious errors but reasonable inferences from limited data, produced by the same cognitive machinery that generates sound reasoning. It also catalogs human cognitive failures (false assumptions, misread evidence) as a secondary explanation for the wilder extensions of soul-belief, such as totemism and fetishism.