The human capacity for altruism—unselfish giving—creates another problem for evolution. As one evolutionist noted: “Anything that has evolved by natural selection should be selfish.” And many humans are selfish, of course. But as he later acknowledged: “It is possible that yet another unique quality of man is a capacity for genuine, disinterested, true altruism. Another scientist added: “Altruism is built into us. Only in humans is it practiced with an awareness of the cost, or sacrifice, that may be involved.