The theories about the origins of humanity contain, for the most part, a strange contradiction. For one thing, we acknowledge that the human mind is basically different from animal intelligence; indeed, there are few writers who question the revolutionary nature of the change that has occurred in the psychic makeup of living beings as a consequence of the advent of conceptual thought, of conscious reflection, and of objective knowledge of the world. “Human intelligence,” writes Le Roy, “presents a completely original, distinctive feature; there is something exceptional and unique about it that is not to be found anywhere else,” while Durkheim observes: “Man is not merely an animal with a few additional attributes, but quite another thing.” “Although the Infusoria are linked to the monkey by a whole series of intermediate stages, the monkey is separated from man by a hiatus,” insists Claparède, and, finally, a writer who is not a scholar expressed the following common-sense judgment on the subject: “We would know exactly what man is if we could accurately assess that insurmountable wall that separates the most ‘intelligent’ animal from the most primitive pygmy.”