It is the group of purely animal instincts that first show themselves in the young, and those even, as we see in the young of the lower animals, generally appear somewhat in the order in which they are required for the individual's good.

Birds just hatched from the egg seem to have, for the first few days, only one instinct ready for action--that of opening their mouths wide at the approach of any thing towards their nest.
Even this instinct is so imperfect and immature that it can not distinguish between the coming of their mother and the appearance of the face of a boy peering down upon them, or even the rustling of the leaves around them by a stick.

In process of time, as their wings become formed, another instinct begins to appear--that of desiring to use the wings and come forth into the air.

The development of this instinct and the growth of the wings advance together.

Later still, when the proper period of maturity arrives, other instincts appear as they are required--such as the love of a mate, the desire to construct a nest, and the principle of maternal affection.
Now there is something analogous to this in the order of development to be observed in the progress of the human being through the period of infancy to that of maturity, and we must not look for the development of any power or susceptibility before its time, nor be too much troubled if we find that, in the first two or three years of life, the animal propensities--which are more advanced in respect to the organization which they depend upon--seem sometimes to overpower the higher sentiments and principles, which, so far as the capacity for them exists at all, must be yet in embryo.