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Sapolsky, Chapter 10: The Evolution of Human Behavior

Evolution 101 — 3 steps

• not so much about survival as reproduction. Antagonistic pleiotropy — sperm early, cancer later.

• other misconceptions — living better adapted than the extinct, not just a “theory”

• sexual selection and natural selection. Example of peacocks — trade offs between two forms of selection.

• sociobiology — evolutionary psychology introduced. Premise: Evolution optimizes social behavior (for fitness) and psychological traits just as it optimizes bodies.

• Marlin Perkins and Mutal of Omaha’s Wild Kingdom. Bad ideas about evolution of altruistic species behavior. Group selection doesn’t work that way.

Individual Selection — 334: competitive infanticide: why langur monkeys kill babies. How females develop a false estrus to fight back. (Working against mountain gorillas these days.)

Kin Selection — 336: Basic idea: your nearest kin has most of your genes. Haldane, “I’d gladly lay down my life for two brothers or eight cousins.” Allomothering. Grooming behaviors reflect closeness. 337: vervet monkey study. Playback studies. These studies show in various ways how warning behaviors track kinship relationships in social primates.

• problem for kin selection — avoiding inbreeding. Many species mate with 1-3rd cousins. Sperm aggregation. Malagasy giant jumping rat. 340 - smell studies — women prefer smell of near relatives over unrelated.

How do animal recognize kin? Major histocompatibility complex (MHC) gives many animals olfactory recognition of kin. Other mechanisms: songs, vaginal fluid smell, milk.

How do we do kin selection? Pseudo-kin selection or “green beard” effects. We are not limited to actual kin, any conspicuous feature (like a green beard). Humans show green beard effects. Related to parochialism and xenophobia.

Reciprocal Altruism.

• don't just think about evolution as promoting competition toward extinction. equilibriums are important.

• reciprocal altruism is a third way that evolution shapes human behavior. Unrelated individuals cooperate across nature (fish in schools, birds in formation, herds). Also unrelated primates. Important 1971 paper by Trivers (344) on reciprocal altruism. how organisms incur a fitness cost to benefit another individual with expectation of reciprocation.

• cheating and freeriding can create a "Red Queen" situation.

Two big questions: when is cooperation optimal, how can altruism start?

What strategy for cooperating is optimal?

• background to Game Theory - John von Neumann. Prisoner's Dilemma connected biologists to game theorists.

• basics of a Prisoner's Dilemma payoff: A&B cooperate: 1 year: A cooperates, B defects: B walks and A gets three years. Cooperation is best, but each individual calculation leads to defection. Quite a little dilemma.

• defection is optimal for single round PD, but what about 3 rounds. Still best to defect. What about "iterated" (uncertain number of rounds)?

• Axelrod's challenge: Optimal strategy for iterated PD. Winner: Anatol Rapoport: Cooperation on 1st round and then match opponent's previous behavior. "Tit for Tat" Always works toward a draw, or slight negative outcome. Not that Tit for Tat tilts toward cooperation, but avoids being a sucker and punishes defectors. famous paper in 1981 by Axelrod and Hamilton.

• "signal errors" can reduce Tit for Tat payoffs. Remedies: "Contrite tit for tat (retaliate after two defections) and Forgiving (forgive 1/3 of defections). Both address the signal error problem, but have other vulnerabilities.

• Mixed (genetic) strategies: You could start out with one strategy and then change to another. How do you go from punitive Tit for Tat to one incorporating forgiveness? Trust. 350-351: describes a changing environment a events signal to individuals to change strategies. Kind of a model of real life.

• Black Hamlet fish

• Stickleback fish

• But sceptical that tit for tat has been found outside humans.

How can altruism start? 353

• on T for T in a population is doomed, two might find each other, Green beard effects might help grow a circle of cooperators. If the cooperating trait included search behaviors for cooperators it would help. Cooperation could also radiate from isolated groups that wind up inbreeding. If reintroduced to a large population, they might influence cooperative payoffs.

Standing on Three legs -- Some examples of different ways that these three forces (ind. selection, kind selection, and reciprocal altruism) can work together in animals.

• vampire bat

• pair bonding (A) vs. tournament species (B) -- what follows: B-males are more violent, A-males need less muscle, in B species a few males do all the reproducing, B-males more likely to screw anything, A-males more likely to share responsibilities. B-species puts more emphasis on sexual selection. 360.

• Parent-Offspring Conflict -- weaning conflict. other biological conflicts between fetus and mother.

• Intersexual Genetic Conflict -- In species with low paternal investment, a father's interest might be with the child and against the mother. "imprinted genes" part of the mechanism for intersexual conflict. Tournament species have more imprinted genes than pairbonding.

Multilevel Selection Theory

• genotype vs. phenotype: phenotype is the expressed individual with its specific traits based on the genotype, which is specific genetic makeup of the individual

• Why it matters -- explanations can be sought at either level. unibrow example. Reviews debate in biology: Dawkins, extreme gene centered - individual genes vs. genome, less radical view, genome centered. Seems to disparge single gene selection somewhat. Gould and Mayr: phenotype trumps genotype. Selection acts on expressed individuals. Dawkins analogy of cake recipe vs. taste of cake. Could be the baker or the recipe if the cakes don't taste right.

• Levels: single gene, genome, single pheotypic trait, collection of traits. These are among the levels in Multi-level Selection.

• Resurrection of Group Selection: Culture (the result of advertising, ideology about cakes, etc.) can also act as a selection force.

• neo-group selection: some heritable traits can be maladaptive for the individual but adaptive for a group. As in the PD, to get the optimal total outcome, you have be willing to forego the best individual outcome. Still controversial. Some biologist might agree that it is possible, but that it is rare. However, among humans it seems to occur alot. Cites "parochial altruism" and role of intergroup conflict in promoting intragroup cooperation.

• credits David Sloan Wilson and E.O Wilson. Quite an "encomeum" there! more reading. famous paper "Rethinking the Theoretical Foundation of Sociobiology"

AND US? How do humans fit into these four modes of selection?

• Individual Selection operates on us, but we do not have the same profile as our ancestors. We are neither clearly pair-bonding nor tournament species (pick your favorite comparative anatomy detail).

• Maybe we are reproductive maximizers? Famous examples of super reproducers in History: Pharaoh Rames II to Genghis Khan. But then we have the Shakers.

• Some evidence of competitive infanticide in abuse and killing by a step parent. (These findings have been challenged, though.)

• Kin Selection: Strong evidence of practices tracking and favoring kin. (Note for later question of "justified partiality".) 368: feuds, bendettas, bequests, dynastic rule, protection against adverse testimony. Humans with damage to vmPFC choose strangers over family. (creepy) Story of the Russian who chose country over family and Stalin's reaction.

• So, lots of evidence, but we also fight wars against people we are highly related to. families fight over succession, patricide, fratricide, we also give to strangers.

370: explanation for why we deviate so much from straight kin selection: we don't do it with MHC or imprinted genes, but we are cognitive (which includes feeling) about it. Evidence from kibutz about turning off sexual interest we "family". 46% would save their dog over a stranger. We can also be manipulated into feeling positive or negative toward others.

• we used to think hunter gatherer bands were highly related, but only about 40%. already reciprocal altruism on the scene there. Conclusion: human do deviate from strict mechanisms of evolution found in other species. (Alfino: We've evolved complex and mixed strategies and can use language and reflection to rethink our behaviors and attitudes.)

• Some challenges: hard to identify heritability for traits related to group selection. Just seems like the most parsimonious explanation.

Second challenge, Is evolution gradual? [This is optional reading.]

Is everything adaptive? [THis is optional reading.]