The first appearance of infancy in the animal world thus heralded the new era which was to be crowned by the development of Man. With the beginnings of infancy there came the first dawning of a conscious life similar in nature to the conscious life of human beings, and there came, moreover, on the part of parents, the beginning of feelings and actions not purely self-regarding. But still more, the period of infancy was a period of plasticity. The career of each individual being no longer wholly predetermined by the careers of its ancestors, it began to become teachable. Individuality of character also became possible at the same time, and for the same reason. All birds and mammals which take care of their young are teachable, though in very various degrees, and all in like manner show individual peculiarities of disposition, though in most cases these are slight and inconspicuous. In dogs, horses, and apes there is marked teachableness, and there are also marked differences in individual character.

But in the non-human animal world all these phenomena are but slightly developed. They are but the dim adumbrations of what was by and by to bloom forth in the human race. They can scarcely be said to have served as a prophecy of the revolution that was to come.