The social instincts, then, are very strong, and they lead us to conform to social rule or sentiment. But now Darwin tells us that in the case of man "images of all past actions and motives would be incessantly passing through the brain." These "images" are mental pictures, and they are printed on those brain cells which make what we call "memory." Now, Darwin tells us that these memory pictures would cause us pain as often as they reminded us that we had broken the social rule or outraged the social sentiment in order to indulge some instinct of a selfish kind. And Darwin makes it clear to us that such a selfish desire may be strong before it is gratified, and may yet leave an impression of pleasure after it is gratified which is weak indeed in presence of the deep-rooted social memories. Let us take a few examples. The desire for a pleasure may be strong enough to drive us to enjoy it, and yet the pleasure may seem to us not worth the cost or trouble after the desire has been sated. When we are hungry the desire for food is intense. After we have eaten we are no longer hungry. But we grow hungry again, and then the desire for food is as intense as ever. Dick Swiveller goes to a bachelor party, and the desire for the convivial glass is strong within him. He drinks too much, and the next morning calls himself a fool for drinking. He is ashamed of his excess, and he has the headache, and the temptation is now absent. But when he is well again, and at another party, the old desire comes back with the old power. So Dick once more indulges too freely in "the rosy," and has another sick head in consequence. And then the social instincts rise up and reproach him, and the sated appetite, being weak, appears to him contemptible. The social instinct is constant: the selfish desire is intermittent. The passion is like a tide which leaps the moral wall and then falls back to low water. The wall remains: it may be sullied or shaken, but it is still a moral wall, and only a long succession of such tides can break it down. When passion has broken down the moral wall the man is at the mercy of his passions. They flood the dwelling of his soul again and again until he is a ruin. This, I think, explains Darwin's idea of the struggle between the social and selfish instincts. In "Adam Bede" George Eliot blames the seducer of Hettie Sorrel for doing a terrible wrong for the sake of a brief selfish indulgence. But that charge is unfair. It implies that the deed was planned and done in cold blood. But the fact was that both Hettie and Arthur were carried away by a rush of passion. The great tide of desire, a desire made terribly strong by Nature, had overleapt the walls of morality and prudence.