The Selfish Gene: 40th Anniversary edition (Oxford Landmark Science) — 12. Nice Guys Finish First

1. 1. In the Iterated Prisoner's Dilemma, the strategy Tit for Tat, which cooperates first then copies the opponent's previous move, won both of Axelrod's computer tournaments.
2. 2. Axelrod defined 'nice' strategies as those that never defect first; all eight nice strategies finished in the top eight of the first tournament.
3. 3. Tit for Tat is also 'forgiving'—it retaliates immediately but then lets bygones be bygones, which helps avoid long runs of mutual recrimination.
4. 4. Axelrod's third 'evolutionary' tournament showed that nice, retaliatory strategies like Tit for Tat dominate in the long run, driving nasty strategies extinct.
5. 5. Tit for Tat is not a true evolutionarily stable strategy because other nice strategies like Always Cooperate can drift in without being noticed, but such strategies are vulnerable to invasion by Always Defect.
6. 6. Local clustering through kinship or population viscosity can help Tit for Tat cross the critical frequency threshold needed to dominate, while Always Defect cannot benefit from clustering.
7. 7. Tit for Tat is 'non-envious'—it never scores more than its opponent, but achieves high shared scores by cooperating, which is optimal in nonzero-sum games.
8. 8. During World War I, a 'live-and-let-live' system emerged in the trenches, where opposing soldiers tacitly cooperated rather than fighting, resembling a Tit for Tat strategy.
9. 9. Vampire bats engage in reciprocal blood-sharing that fits the Iterated Prisoner's Dilemma, with donors preferentially feeding unrelated roostmates who have helped them before.
10. 10. Fig trees retaliate against cheating fig wasps by aborting figs if the wasp lays too many eggs and pollinates too few flowers.
11. 11. Hermaphrodite sea bass take turns playing male and female roles in a Tit for Tat fashion; pairs with uneven sharing tend to break up.
12. 12. The success of nice, forgiving, non-envious strategies in the Iterated Prisoner's Dilemma shows that cooperation can flourish even in a fundamentally selfish world, provided the shadow of the future is long.