In this way, say the advocates of this theory, we may account for the fact that the animal has no adequate knowledge of what he is doing when he performs an act instinctively; he has no end or aim in his mind; he simply feels his nervous system doing what it is fitted to do by its organic adaptations to the stimulations of air, and earth, and sea, whatever these may be.
But it may be asked: Why do succeeding generations improve each on its parents, so that there is a gradual tendency to perfect the instinct?
The answer to this question brings up another great law of biology--the principle of Variations.

This principle states the common fact that in every case of a family of offspring the individual young vary slightly in all directions from their parents.

Admitting this, we will find in each group of families some young individuals which are better than their parents; these will have the advantage over others and will be the ones to grow up and have the children of the next generation again, and so on.

So by constant Variation and Natural Selection--that is, the "Survival of the Fittest" in competition with the rest--there will be constant improvement in the Instinct.
2.

The other theory, the rival one, holds that there are some instincts which show so plainly the marks of Reason that some degree of intelligent adjustment to the environment must be allowed to the animal in the acquiring of these functions.