For much of history, such willingness to die has been regarded as something admirable and courageous, as a part of human duty. Paradoxically, that is a direct consequence not of our aggression but of our extreme sociability and willingness to cooperate. If we can become not only ourselves, but our families, teams and countries, cooperation comes easily to us, relying on the same deeply innate mechanisms that drive us (and other creatures) to protect our very bodies.
