I have endeavoured in this chapter briefly to show that the mental qualities of our domestic animals vary, and that the variations are inherited.

Still more briefly I have attempted to show that instincts vary slightly in a state of nature.

No one will dispute that instincts are of the highest importance to each animal.

Therefore, there is no real difficulty, under changing conditions of life, in natural selection accumulating to any extent slight modifications of instinct which are in any way useful.

In many cases habit or use and disuse have probably come into play.