The Selfish Gene: 40th Anniversary edition (Oxford Landmark Science) — 10. You Scratch My Back, I’ll Ride on Yours

1. 1. W. D. Hamilton's 'selfish herd' model shows that individuals reduce their domain of danger by moving toward the center of a group, leading to aggregation without cooperation.
2. 2. Bird alarm calls are not necessarily altruistic; the 'cave' theory suggests the caller warns others to avoid attracting the predator itself.
3. 3. The 'never break ranks' theory explains alarm calls as a way to ensure the whole flock flies off together, so the caller does not become an isolated target.
4. 4. Zahavi's theory proposes that stotting in Thomson's gazelles is a selfish signal to predators, advertising the individual's fitness and directing the chase elsewhere.
5. 5. In Hymenoptera, a female is more closely related to her full sisters (relatedness 3/4) than to her own offspring (1/2), which predisposes worker sterility.
6. 6. Trivers and Hare found that in many ant species, the investment ratio of female to male reproductives is close to 3:1, supporting the theory that workers control the sex ratio.
7. 7. In slave-making ant species, the sex ratio shifts to 1:1 because slave workers are unrelated to the brood and cannot counter the queen's manipulation.
8. 8. Reciprocal altruism can evolve as an evolutionarily stable strategy when individuals recognize and remember each other, as shown by the 'Grudger' strategy in computer simulations.
9. 9. Cleaner-fish and their clients exhibit delayed reciprocal altruism, stabilized by site-tenacity that allows clients to return to reliable cleaners and avoid mimics.
10. 10. Trivers suggests that human psychological traits like guilt and gratitude evolved to improve cheating, detecting cheats, and maintaining reciprocal altruism.