Altruism, collective rationality, and extreme self-sacrifice.

Puzzlement about extreme self-sacrifice arises from an unarticulated assumption of psychological egoism, according to which people invariably act in their own self-interests. However, altruism and collective rationality are well established experimentally: people sometimes act to benefit others or in the interests of groups to which they belong. When such social motives are sufficiently strong, extreme self-sacrifice presents no special problem of explanation and does not require out-group threats.