Selfishness has come to be called "bad" because it injures the many without benefiting the one. Unselfishness has come to be called "good" because it brings benefit and pleasure to one and all. "It is twice bless'd: it blesseth him that gives and him that takes." As Marcus Aurelius expresses it: "That which is not for the interest of the whole swarm is not for the interest of a single bee." And again he puts it: "Mankind are under one common law; and if so they must be fellow-citizens, and belong to the same body politic. From whence it will follow that the whole world is but one commonwealth." And Epictetus, the Greek slave, said that as "God is the father of all men, then all men are brothers." For countless ages this notion of human brotherhood, and of the evil of self-love, has been to morality what the sap is to the tree. And now let us think once more how the notion first came into being. I said that morality--which is the knowledge of good and evil--did not come by revelation from God, but by means of evolution. And I said that this idea was first put forth by Spencer and Darwin, and afterwards dealt with by other writers. Darwin's idea was two-fold. He held that man inherited his social instincts (on which morality is built) from the lower animals; and he thought that very likely the origin of the social instinct in animals was the relation of the parents to their young. Let us first see what Darwin said. In Chapter Four of _The Descent of Man_ Darwin deals with "moral sense." After remarking that, so far as he knows, no one has approached the question exclusively from the side of natural history, Darwin goes on: The following proposition seems to me in a high degree probable--namely, that any animal whatever, endowed with well-marked social instincts, the parental and filial affections being here included, would inevitably acquire a moral sense, or conscience, as soon as its intellectual powers had become as well, or nearly as well, developed as in man. For, firstly, the social instincts lead an animal to take pleasure in the society of its fellows, and feel a certain amount of sympathy with them, and to perform various services for them.... Every one must have noticed how miserable dogs, horses, sheep, etc., are when separated from their companions, and what strong mutual affection the two former kinds, at least, shown on their reunion.... All animals living in a body, which defend themselves or attack their enemies in concert, must indeed be in some degree faithful to one another; and those that follow a leader must be in some degree obedient. When the baboons in Abyssinia plunder a garden, they silently follow a leader, and if an imprudent young animal makes a noise, he receives a slap from the others to teach him silence and obedience....