Consider the fact that human action ranges to the extremes. People can perform extraordinary acts of altruism, including kindness toward other species — or they can utterly fail to be altruistic, even toward their own children. So whatever tendencies we may have inherited leave ample room for variation; our choices will determine which end of the spectrum we approach. This is where ethical discourse comes in — not in explaining how we’re “built,” but in deliberating on our own future acts. Should I cheat on this test? Should I give this stranger a ride? Knowing how my selfish and altruistic feelings evolved doesn’t help me decide at all.