A wonderful piece of writing by William James: 

“Why do we smile, when pleased, and not scowl? Why are we unable to talk to a crowd as we talk to a single friend? Why does a particular maiden turn our wits so upside-down? The common man can only say, Of course we smile, of course our heart palpitates at the site of a crowd, of course we love the maiden, that beautiful soul clad in that perfect form, so palpably and flagrantly made for all eternity to be loved! 

And so, probably, does each animal feel about the particular things it tends to do in the presence of particular objects… To the lion it is the lioness which is made to be loved; to the bear, the she-bear. To the broody hen the notion would probably seem monstrous that there should be a creature in the world to whom a nestful of eggs was not the utterly fascinating and never-to-be-too-much-sat-upon object which it is to her. 

Thus we may be sure that, however mysterious some animals’ instincts may appear to us, our instincts will appear no less mysterious to them.” From The Principles of Psychology.