Transcript: Robert Sapolsky on Behavioral Evolution II at Stanford

Stanford professor Robert Sapolsky discusses Behavioral Evolution II in detail at Stanford. In this evolution lecture, he focuses on individual and kin selection, behavioral logic, competitive infanticide, male/female animal hierarchies, sex-ratio fluctuation, intersexual competition, imprinted genes, sperm competition, inbred-founder populations, group and multi-level selection, and punctuated equilibrium. This lecture presentation occurred on April 2, 2010.

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Robert Sapolsky – Stanford professor

Let’s get going. Various announcements, procedural things. A number of people want more information about grading and what the exams are like, all of that. I think I mentioned one-third of the points will come from the midterm, two-thirds from the final. In terms of the style of the midterm, the midterm is heavily going to be about making sure you got down all the factoids from the first half of the course, that you’ve got the basics of each of our proverbial buckets. The second half of the final is all going to be about integration, thinking across the different categories. So just a sense of that.

Readings. Readings, as they are coming out, the books are not required until the second half of the course. The handout on Monday, I think, said which chapters of the Zebra book you should read. We will shortly get to you which chapters of the Chaos book you should read as well. The readings that are being posted on the CourseWorks, the downloads of various published papers, those are required. I’m clear on those whether this is a paper you should read all of, if this is one you should read the abstract of. Even if you read all of, do not read it in some obsessive, detail-oriented way. The goal is probably to be able to say, in one or two paragraphs, why this paper has something pertinent to say about the topic they fell into. You’re not sitting there having to memorize techniques, middle names of the authors, how many animals, anything like that.

In terms of that, it probably makes sense to read those after the first lecture of whatever block there is. And hopefully, if I get organized, I’ll be able to get you sort of a list of the readings further in advance than one week in advance. Nonetheless, you should probably hold off reading it until after the lecture occurs.

Let’s see. What else? People wanted to get a sense of how long things were going to go. And as we’ll see today, the evolution lecture topic will cover two classes. Molecular genetics, which is what we’ll pick up on Monday, I’m guessing one to one and a half. Behavior genetics following that, one to one and a half, ethology one. Neurobiology, endocrinology, we’ll have one week devoted to intro to the topics. And again, that’s one where this is so important for everybody to be up to speed rather than these being in catch-up sections that week. The whole week, Monday, Wednesday, Friday, will be devoted to that with the TAs teaching it. The following week, three more lectures, more advanced ones. And depending on proximity to the midterm, there may be a half-lecture in there on statistics, or maybe not. So this is going to depend on keeping on schedule. This is a rough approximation. The midterm is going to be a Monday night. You will be responsible for material up to the previous Wednesday, and there will be lots of review stuff. Take a look at the extended notes being posted.

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What else? OK. I think that covers most of the procedural stuff. All of this stuff will get posted as well.

So picking up on the other day. What was happening the other day? Number one, the trouncing of Darwin inventing evolution, trouncing of survival of the fittest, probably most importantly, trouncing of behavior for the good of the species, group selection-type arguments. What we saw was, number one, the rationale for the whole thing. There is a vicious, un-fightable logic to why hearts have to be the size they are and kidneys have the filtration rates they have to have in order to solve the challenges of leaving as many copies of your genes in the next generation. And making sense of the evolution of hearts and kidneys and things like that could be the worlds of bioengineers and biomechanics folks with an underlying logic that it’s got to be something that increases the number of copies of genes that you leave.

And the whole rationale for Wednesday’s lecture and today is applying the same sort of logic to behavior. The whole world of just as you can optimize sort of the way one’s neck, how long it is if you’re a giraffe, you can optimize behavioral strategies. And again, also throwing in a caveat, no animal is sitting there, maybe with the exception of some other apes, sitting there consciously strategizing along those lines. One saying, so what would you, as this dandelion, want to do at that point with this ecological challenge, personifying just to make things easier.

What we then barreled into were the three major building blocks for thinking about the evolution of behavior in the framework of contemporary evolutionary thinking. Number one, individual selection — passing on as many copies of your own genes to the next generation as possible by way of your own reproducing. The individual selection — a chicken is an egg’s way to make another egg. I’ve now rehearsed that, so I’ve got that down right. The whole notion of behavior as just being this epiphenomenon in order to do what’s needed to get another copy of the genes into the next generation.

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.

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.

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.

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.