Cooperation in Nature

The tournament result spilled into biology, and it answered a question philosophers had argued over for centuries: why would selfish creatures ever help one another?

The math gave a clean answer. Cooperation can survive among selfish agents when interactions repeat and each side remembers the last one. Biologists call this reciprocal altruism, and nature is full of it: vampire bats share blood with hungry neighbors who shared with them before, and monkeys groom partners who groom them back. Over the long run, paying it forward pays off.