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Transcript: Robert Sapolsky on Behavioral Evolution II at Stanford

Building block number two. Some of the time, the best way to increase the number of genes you pass on to the next generation is to help your relatives do so following that logic of Mendelian relatedness. And people in the catch-up section, I know, went over issues of, why is it that you share half your genes with a full sibling, a quarter with a half sibling, et cetera? So sometimes the way to maximize is by helping out a relative to do so with, again, constrained by this vicious mathematical logic of, it depends on how related you are to the relative. And thus, you will gladly lay down your life for one identical twin, two full siblings, eight cousins. Off you go.

So the whole notion there of insight into why social animals the galaxy over are so obsessed with kinship and relatedness, the whole world of who counts as an us, who counts as a them in terms of cooperative behaviors playing out along lines of relatedness.

Finally, we saw the third piece, which was reciprocal altruism. You scratch my back, I’ll scratch yours. Many hands make the task less scratchy or whatever. And what you see in those cases, there is a whole world in which you don’t have to be related to have cooperation. And we saw all the domains of that bringing in the formalization — biomechanics person figuring out how strong a leg bone has to be. A game theorist figuring out within the realm of social behavior when you cooperate and when you don’t and what sort of strategies. Game theory, of seeing the prisoner’s dilemma as the building block of that entire field and seeing all the strategies worked out by mathematicians and economists and diplomats and seeing which ones optimize under what circumstance. And then going and look in the real world and seeing there’s all sorts of animals out there that have evolved optimization strategies of when to cooperate and when to defect.

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And what we’ll get to as a huge, huge issue by the time we get to the lectures on aggression, cooperation, et cetera is, well, that’s great when you’ve got a cooperative system going. How do they ever start? How do you jump start cooperation in systems? The evolution of cooperation, that’s something we will get to in great detail down the line.

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Finally, what we shifted to was now saying, great, we’ve got all these principles in hand here and our big three building blocks and all of that. How would it be applied to making sense of animal behavior out in the real world? And we left with the examples starting someplace there — where did it go, yes, that’s it — of us marching through, know one individual factoid about some species or other species, know that there’s a big difference between the genders in size or there isn’t, know that there’s not high levels of aggression in males, know that females always give birth. Whatever those traits are as we marched through, using these ideas about individual selection, kin selection, reciprocal altruism, you could march through and logically infer what the social behavior of this particular species was going to be like, and you would be right. We saw, for example, in tournament species, tournament species where you have high levels of aggression among males, male-male competition for access to females. As a result, males tend to be a lot bigger than females. They are being selected for muscle mass, secondary sexual characteristics, plumage, big sharp canines for slashing the other guy.

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Bringing up this issue of, in a tournament species, who does the male want to mate with? What sort of female are males interested in mating with? The answer being, anyone who will mate with them because there’s like no cost involved. All that’s involved is no parental behavior, none of that, the cost of sperm. And literally, people analyze the relative cost of sperm versus eggs in tournament species. Males are dramatically un-choosy as to who they mate with. In tournament species, males have dramatic variability in reproductive success — 5% accounting for 95% of the matings.

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Female choice in a tournament species. What does a female want out of a male? She certainly is not going to get good fatherhood out of the guy. All she wants are good genes because that’s all she could hope for from the guy. A whole world of female selectivity for markers of good genes. And as we’ll see in the sexual behavior lectures, a whole world of males trying to fake out females across the animal world, suggesting they got better genes than they actually do. So we will come to that.

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Then tournament species. Do you see female abandonment of kids? Absolutely not, because there’s nobody else who’s going to take care of them. Coupled with that, you see single births among those species, low level. High levels of aggression amongst the males, low levels of parenting. And males tend to live a lot shorter than females.

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And what we saw at the other end, the pair-bonded species was a completely different picture. Males are being careful who they’re mating with because the wiring there is you mate, you take care of the kids. High levels of male parenting, females are thus able to abandon them. Females can have multiple births. Males are selected to be as close to females as a male can be. So there’s not a big difference in size. There’s not a big difference in secondary sexual characteristics. There’s not high levels of aggression. There’s not big differences in lifespan.

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Who does a female want to mate with? Someone who is going to be a competent father. Thus the whole world of pair-bonded species, where males court with rituals of coming up with food and coming up with things of that sort. So the most striking thing about that was, again, going back to the two skulls I brought in, you could know nothing more about that species other than this is an adult female, this is an adult male. And working through the same logic, you know a huge amount about the private lives of the species and who’s messing around with who in the bushes. And that’s merely by applying these principles.

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By Pangambam S

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