When people learn just a little about game theory, decision theory, economics, or even evolutionary theory, they sometimes come away thinking that altruism is somehow “irrational,” or that rational agents are selfish. Here are reasons why altruism is often rational:

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1. Intrinsic values: as a psychological fact, most humans intrinsically value at least some things as ends (not merely as means to other ends) that are not about their own gain. For instance: reducing suffering around the world, or the flourishing of the people in their country.

2. Relationships: altruistic people tend to have stronger, happier, more goal aligned and mutually beneficial relationships. While in theory a purely selfish person can have highly beneficial relationships, these expedient tit-for-tat relationships are much harder to make work.

3. Evolution: there are multiple reasons evolution programmed most of us with genuine altruism, even though it optimizes for gene spread.

Altruism is rewarded in settings of:
i) raising children
ii) iterated games
iii) tribal loyalty w/ punishment of defectors
iv) lie detection

4. Warm glow: most humans find that it gives them happiness to do altruistic acts. I call this “the Lucky Fact” about human nature. It’s both important and very lucky. We feel good to see others that we like feel good, and we feel good about ourselves when we cause good feelings.

5. Pre-commitment: suppose there was a world of highly rational, purely selfish beings. If they were able, they might pre-commit (jointly, as a group) to become partially altruistic, as a way to help solve difficult collective action problems. By uniting goals they mutually gain.