WEBVTT - Why do animals cooperate? 0:00:00.120 --> 0:00:04.480 Howdy, Extraordinaries. Most of this episode is about social behavior 0:00:04.559 --> 0:00:09.400 and cooperation in animals, and in particular human animals, but 0:00:09.560 --> 0:00:12.479 towards the end we talk a little bit about cases 0:00:12.600 --> 0:00:16.680 where humans and non human animals have not gotten the 0:00:16.760 --> 0:00:20.000 love that they deserve early on in life, in the 0:00:20.079 --> 0:00:23.119 implications of that for their behavior, which is a little 0:00:23.120 --> 0:00:26.240 bit hard to hear, So just a heads up so 0:00:26.280 --> 0:00:28.520 you can decide if you want to listen to the 0:00:28.600 --> 0:00:40.519 last third of the episode or not. Thanks. Natural selection 0:00:40.920 --> 0:00:44.320 doesn't exactly sound like the kind of mechanism that would 0:00:44.360 --> 0:00:48.440 result in a lot of cooperation and snugly social behavior. 0:00:49.040 --> 0:00:53.280 Let's imagine it. You take variation in some trait, say 0:00:53.880 --> 0:00:58.480 differences in running speed, and link that trait to survival 0:00:58.560 --> 0:01:02.960 and reproduction. And so imagine that running speed determines who 0:01:03.160 --> 0:01:06.160 escapes from predators and then goes on to survive and 0:01:06.200 --> 0:01:09.840 have babies. And if that trait is heritable, so if 0:01:09.840 --> 0:01:14.080 the babies of fast parents are fast themselves, then you 0:01:14.120 --> 0:01:18.240 have all the ingredients necessary for natural selection. Over time, 0:01:18.640 --> 0:01:22.920 you'd expect that fast individuals survive and become more common, 0:01:23.319 --> 0:01:29.160 while the slow individuals, well, they get eaten. That sounds 0:01:29.240 --> 0:01:33.280 kind of cutthroat, Yet somehow we've still ended up in 0:01:33.319 --> 0:01:37.160 a world where animals will call out to warn others 0:01:37.200 --> 0:01:40.880 of a nearby predator, even if calling out increases the 0:01:41.000 --> 0:01:44.880 risk that the predator goes after the caller in particular, 0:01:45.640 --> 0:01:48.520 and honey bees will sting us to protect their hive mates. 0:01:48.920 --> 0:01:52.000 Even though stinging us will pull out their stinger and 0:01:52.080 --> 0:01:57.200 effectively disembowel the bee. They give their lives to protect 0:01:57.240 --> 0:02:00.600 their buddies living inside the hive. So how did this 0:02:01.160 --> 0:02:05.720 seemingly brutal mechanism give rise to so much cooperation and 0:02:05.800 --> 0:02:09.000 helpful behavior. That's what we're going to talk about today. 0:02:09.720 --> 0:02:13.560 Welcome to Daniel and Kelly's surprisingly cooperative universe. 0:02:26.840 --> 0:02:27.040 Hi. 0:02:27.200 --> 0:02:30.560 I'm Daniel. I'm a particle physicist, and I think people 0:02:30.680 --> 0:02:33.800 are the most interesting thing in the universe and also 0:02:33.960 --> 0:02:34.960 the most terrifying. 0:02:35.320 --> 0:02:38.800 Oh hello, I'm Kelly. I study parasites and space and 0:02:38.840 --> 0:02:41.960 I completely agree with Daniel's assessment, and at the end 0:02:42.000 --> 0:02:45.720 of this episode when I describe human behavior, I will 0:02:45.760 --> 0:02:46.560 try not to cry. 0:02:49.160 --> 0:02:51.720 So my question for you today, Kelly is do you 0:02:51.800 --> 0:02:55.560 consider yourself an introvert or an extrovert? And when did 0:02:55.600 --> 0:02:55.880 you know? 0:02:56.320 --> 0:03:00.120 Oh? Yeah, definitely an introvert. I think I hide it well, 0:03:00.160 --> 0:03:02.680 but I very much enjoy hanging out with people. But 0:03:02.800 --> 0:03:05.600 at the end of like a conference or something, I 0:03:05.680 --> 0:03:11.799 will crawl into my bed and like just be absolutely exhausted. 0:03:13.040 --> 0:03:15.680 And I get very nervous when I go in a 0:03:15.760 --> 0:03:18.360 room and I have to like pick a group to 0:03:18.440 --> 0:03:20.919 go hang out with because I assume that nobody really 0:03:20.919 --> 0:03:23.920 wants to talk to me, And so I love situations 0:03:23.919 --> 0:03:25.800 where people come up to talk to me because then 0:03:25.800 --> 0:03:28.120 I don't feel like I'm putting anyone out. So if 0:03:28.160 --> 0:03:30.400 you ever see me somewhere, feel free to come up 0:03:30.440 --> 0:03:32.920 and talk to me, because that relieves the pressure on 0:03:33.000 --> 0:03:36.120 me and makes me feel so much better. And I 0:03:36.160 --> 0:03:37.920 don't know when I realized that. I think it was 0:03:37.960 --> 0:03:43.080 probably in undergrad when I had to like start meeting people. Yeah, 0:03:43.120 --> 0:03:44.200 I guess I don't know what about you. 0:03:44.480 --> 0:03:47.240 I'm not sure how I would classify myself, because on 0:03:47.320 --> 0:03:50.119 one hand, I feel the same way at the end 0:03:50.360 --> 0:03:52.680 of a lot of socializing that like at a conference 0:03:52.920 --> 0:03:54.960 when it was like, hey, let's go out to dinner 0:03:55.000 --> 0:03:59.040 and I'm like, no, thank you. But also I find 0:03:59.040 --> 0:04:02.120 that people are my best source of energy, you know, 0:04:02.200 --> 0:04:04.640 if I go and teach in the classroom. I love 0:04:04.880 --> 0:04:08.840 that engagement and the response. I love getting emails from listeners. 0:04:08.880 --> 0:04:12.320 I love hanging out with friends, Like moments laughing with 0:04:12.360 --> 0:04:15.880 your friends are more enjoyable than anything you could ever 0:04:16.040 --> 0:04:19.159 do by yourself. Yeah, and so people are like the 0:04:19.200 --> 0:04:22.400 greatest mystery and source of joy and happiness in the universe. 0:04:22.400 --> 0:04:24.360 And also they are completely exhausting. 0:04:24.560 --> 0:04:24.800 Yeah. 0:04:24.839 --> 0:04:27.280 So I'm not sure where that puts me on the spectrum. 0:04:27.320 --> 0:04:33.159 Maybe we're exo introverts intro exoverts. Because I agree, I like, 0:04:33.240 --> 0:04:36.880 I also really look forward to going to conferences because 0:04:36.920 --> 0:04:39.839 I cannot wait to see the people at conferences and 0:04:39.880 --> 0:04:42.599 hear about how they were doing and laugh about stuff 0:04:42.640 --> 0:04:44.880 and find out if they purposefully infected themselves with any 0:04:44.920 --> 0:04:48.680 parasites in the last year, and you know, all that stuff. 0:04:48.680 --> 0:04:50.080 But you know, on the other hand, at the end 0:04:50.080 --> 0:04:51.240 of the day, I am also like. 0:04:51.640 --> 0:04:55.160 I need to see Yeah, exactly. Well, today we are 0:04:55.200 --> 0:04:57.800 not just telling personnel stories. We are talking about the 0:04:57.920 --> 0:05:01.880 larger question of human being behavior. Why do people act 0:05:01.920 --> 0:05:04.400 the way they do? Is it driven by evolution or 0:05:04.560 --> 0:05:08.520 something else? Even weirder, and today's episode is inspired by 0:05:08.520 --> 0:05:10.360 a question we got from an eleven year. 0:05:10.279 --> 0:05:13.880 Old, didn't we Actually they're thirteen years old now and 0:05:13.920 --> 0:05:16.400 they are the child of some friends of mine, and 0:05:16.440 --> 0:05:19.960 I was super excited to get their questions. So let's 0:05:19.960 --> 0:05:21.000 go ahead and listen to it. 0:05:21.400 --> 0:05:24.039 Hi, Daniel and Kelly, I love your podcast, And I 0:05:24.080 --> 0:05:27.560 have a question why did humans evolve to be social? 0:05:27.760 --> 0:05:30.039 And why do we go crazy if we're isolated for 0:05:30.120 --> 0:05:32.479 too long? I also want to know what happened at 0:05:32.520 --> 0:05:34.719 the human related it's whole life without having contact with 0:05:34.760 --> 0:05:40.080 other humans, and why could some animals like whales go 0:05:40.200 --> 0:05:43.440 for so long without having contact with other whales but 0:05:44.160 --> 0:05:46.720 humans can, thanks, all right? 0:05:46.760 --> 0:05:48.400 So on one hand, this is a really fun question, 0:05:48.440 --> 0:05:52.880 but also a really deep question about evolution, because like 0:05:52.880 --> 0:05:56.960 the whole foundation of modern biology is evolution and natural selection, 0:05:57.080 --> 0:05:59.680 and things are the way they are because of this process, 0:06:00.120 --> 0:06:02.640 and that forces us to think about everything we see 0:06:02.880 --> 0:06:05.560 through that lens. But it can sometimes be hard to 0:06:05.640 --> 0:06:09.000 understand how something evolved to exist. You know, you have 0:06:09.000 --> 0:06:11.760 the examples of the eye and stuff, but human behavior 0:06:11.880 --> 0:06:14.279 is a great example. So tell us, Kelly, how do 0:06:14.360 --> 0:06:15.360 you interpret this question. 0:06:15.680 --> 0:06:17.760 Well, I'll be honest, I kind of put this question 0:06:17.839 --> 0:06:19.760 off for a while because I was like, Okay, I'm 0:06:19.760 --> 0:06:21.279 going to I'll look it up real quick and see, like, 0:06:21.279 --> 0:06:24.279 you know, what are people saying these days? And generally 0:06:24.480 --> 0:06:27.560 the answer I found was, oh, well, humans are social 0:06:27.640 --> 0:06:31.080 because it benefited us in our evolutionary past. And I 0:06:31.080 --> 0:06:35.919 was like, yeah, okay, well yeah, but how and like 0:06:35.960 --> 0:06:38.680 there's got to be a richer answer to that. But 0:06:38.839 --> 0:06:41.840 there was generally not a much richer answer. And I 0:06:41.880 --> 0:06:43.080 think at the end of the day, it's hard to 0:06:43.120 --> 0:06:46.800 know for a particular species why a behavior arose, in 0:06:46.839 --> 0:06:49.120 part because behaviors don't leave fossils. But at the end, 0:06:49.160 --> 0:06:51.120 I'm going to try to give a much better answer. 0:06:51.520 --> 0:06:55.000 But I thought that we could start by taking a 0:06:55.040 --> 0:06:59.320 look at why we think we see cooperation and social 0:06:59.320 --> 0:07:03.280 behavior in general in animals at all, because actually that's 0:07:03.279 --> 0:07:04.880 a little bit of a Darwinian puzzle. 0:07:04.960 --> 0:07:08.000 Yeah, I agree, it's really a fascinating question. On one hand, 0:07:08.040 --> 0:07:11.120 it seems like maybe it's simple because people learn to 0:07:11.120 --> 0:07:15.000 cooperate because that's more effective. But if everybody else is cooperating, 0:07:15.080 --> 0:07:17.240 then like the one jerk who's like lazy and then 0:07:17.320 --> 0:07:19.720 just steals the results of the mammoth hunt is going 0:07:19.800 --> 0:07:23.840 to benefit. So it's not obvious why cooperation is always 0:07:23.840 --> 0:07:26.240 a successful strategy. That's how you have to think about. 0:07:26.000 --> 0:07:28.400 It, right, yeah, right, exactly. So in order for natural 0:07:28.400 --> 0:07:32.000 selection to happen, you have to have variation in a trait. So, 0:07:32.080 --> 0:07:36.360 for example, maybe you have variation in speediness, and then 0:07:36.440 --> 0:07:40.080 that variation needs to be important for survival and reproduction. 0:07:40.240 --> 0:07:43.960 So maybe the faster individuals are able to run away 0:07:44.000 --> 0:07:46.960 from the predator and then they survive to reproduce, right, 0:07:47.080 --> 0:07:50.680 and that trait needs to be passed from parents to offspring, 0:07:50.800 --> 0:07:54.960 So the faster parents makes faster offspring, and over time 0:07:55.040 --> 0:07:58.200 you end up with faster individuals in the population, and 0:07:58.440 --> 0:08:01.640 the genes that produce faster individuals become more common in 0:08:01.640 --> 0:08:06.840 the population. And that doesn't necessarily sound like a mechanism 0:08:06.920 --> 0:08:10.600 that would result in more like hugs and cooperation. That 0:08:10.640 --> 0:08:12.640 seems like a bit of a cutthroat thing. You know, 0:08:12.680 --> 0:08:15.080 if you are faster and better able to get away 0:08:15.080 --> 0:08:17.320 from the predators, are better able to secure the food, 0:08:17.800 --> 0:08:19.920 then you're the one who gets to reproduce and you're 0:08:19.960 --> 0:08:22.560 the one who, you know, gets to pass your genes 0:08:22.560 --> 0:08:25.080 to the next generation. But when when look out in 0:08:25.160 --> 0:08:29.080 nature we see tons of cooperation. So you know, for example, 0:08:29.240 --> 0:08:32.920 honey bees, if you walk up to a honeybee nest okay, 0:08:33.040 --> 0:08:37.080 and you disturb the nest, do not recommend a honey 0:08:37.080 --> 0:08:39.480 bee will come out and they'll sting you. And they've 0:08:39.480 --> 0:08:41.960 got these barbed stingers that get stuck in your skin, 0:08:42.520 --> 0:08:46.480 and so the stinger will stay behind and the venom 0:08:46.520 --> 0:08:49.920 gland and like the insides of the honey bee will 0:08:49.920 --> 0:08:52.319 get pulled out of the bee. The bee will get 0:08:52.360 --> 0:08:56.360 disemboweled and will die to protect its hive mates. And 0:08:56.400 --> 0:08:59.240 so that bee is giving its life to protect the 0:08:59.280 --> 0:09:02.040 rest of the hive. And we see ants that are 0:09:02.080 --> 0:09:05.400 willing to, for example, like plug the whole of a 0:09:05.480 --> 0:09:07.880 nest overnight, even though the temperature is going to kill 0:09:07.880 --> 0:09:10.160 them overnight. They give their lives to like protect the 0:09:10.160 --> 0:09:12.840 temperature for the rest of their hivemates. And we see 0:09:12.880 --> 0:09:16.480 just loads of examples of animals dying for you know, 0:09:16.640 --> 0:09:19.120 their buddies, and you know, why does that happen? 0:09:19.360 --> 0:09:21.280 And so this is a great analogy, for example, to 0:09:21.440 --> 0:09:23.600 like soldiers dying in a war. Right, they're not going 0:09:23.679 --> 0:09:27.560 to be around to experience the benefits of victory, and 0:09:27.640 --> 0:09:29.959 yet they give up their lives. But then it's always 0:09:30.000 --> 0:09:32.720 easier to understand these things in terms of like ants 0:09:32.720 --> 0:09:35.960 and bees because you can actually do experiments on them ethically. Right, Yes, 0:09:36.080 --> 0:09:39.640 so what do we know about why honey bees act altruistically? 0:09:39.960 --> 0:09:43.240 Is it because they have like more sophisticated genetic relationships 0:09:43.600 --> 0:09:47.440 among themselves and with their queens or what's the story? 0:09:47.720 --> 0:09:50.280 Yes, absolutely so that is part of it. But first 0:09:50.320 --> 0:09:51.880 I want to dig down a little bit more and 0:09:51.920 --> 0:09:56.600 clarify what level we think evolution is happening at. Evolution 0:09:56.840 --> 0:09:58.880 at the end of the day, is just changes in 0:09:58.960 --> 0:10:02.120 gene frequencies over time. So when we were talking about 0:10:02.600 --> 0:10:06.319 natural selection happening for fastness, like being able to run 0:10:06.360 --> 0:10:10.040 away from the predators, evolution happening there, you'd end up 0:10:10.080 --> 0:10:14.000 with a higher frequency of the types of genes that 0:10:14.040 --> 0:10:18.040 are associated with moving quickly. So over time, the versions 0:10:18.080 --> 0:10:20.800 of the genes for slow individuals go away and you 0:10:20.840 --> 0:10:23.319 get more of the versions of the genes for fast individuals. 0:10:23.400 --> 0:10:24.120 Does that make sense? 0:10:24.240 --> 0:10:26.600 It does make sense, But it sounds like you're choosing 0:10:26.720 --> 0:10:31.240 this set of words gene frequencies changing over time through 0:10:31.320 --> 0:10:35.120 natural selection very specifically, maybe in contrast to something you 0:10:35.200 --> 0:10:37.640 imagine is in the minds of the listeners or a 0:10:37.720 --> 0:10:41.360 general misunderstanding of evolution. What are you contrasting this with, Well. 0:10:41.240 --> 0:10:44.040 So I'm eventually going to make the point that individuals 0:10:44.080 --> 0:10:46.560 are the ones who are carrying these genes around, and 0:10:46.679 --> 0:10:48.840 selection is going to be happening at the level of 0:10:48.960 --> 0:10:51.440 individuals and not the level of groups. 0:10:51.880 --> 0:10:54.240 I see. So it's not like evolution is this like 0:10:54.400 --> 0:10:59.240 mastermind guiding some species towards some predetermined goal or something. 0:10:59.280 --> 0:11:01.600 It's just a bunch of individuals changing over time. 0:11:01.760 --> 0:11:04.040 Yeah, it's a frequency of genes that are found in 0:11:04.080 --> 0:11:06.720 a population, and those genes are carried by individuals that 0:11:07.080 --> 0:11:08.840 some of which will die and some of which will not. 0:11:09.080 --> 0:11:11.920 All right, yeah, okay, so individuals are carrying around these genes. 0:11:11.920 --> 0:11:13.920 And then in the nineteen sixties there was this guy, 0:11:14.120 --> 0:11:17.959 when Edwards, who was arguing that selection might be happening 0:11:18.000 --> 0:11:20.560 at the level of like groups, or maybe even at 0:11:20.559 --> 0:11:23.760 the level of species, and this idea kind of makes sense. So, like, 0:11:23.840 --> 0:11:26.800 you know, you look around and there's for example, maybe 0:11:26.880 --> 0:11:31.120 rodents having two babies each, and you might say, oh, okay, 0:11:31.160 --> 0:11:33.120 two babies, that's not a lot of babies. Maybe what 0:11:33.160 --> 0:11:35.240 they're doing is they're trying to not eat all of 0:11:35.280 --> 0:11:37.160 the seeds. They're trying to make sure that they don't 0:11:37.480 --> 0:11:40.080 over exploit the seeds for the good of the species. 0:11:40.080 --> 0:11:41.800 They want to make sure that they're able to survive 0:11:41.840 --> 0:11:42.920 for many generations. 0:11:43.160 --> 0:11:45.120 What considerate and well organized rote. 0:11:45.360 --> 0:11:48.559 Yes, yes, you know, maybe we should take some lessons 0:11:49.440 --> 0:11:53.040 from their behavior, but unfortunately it turns out that we 0:11:53.280 --> 0:11:58.040 don't actually usually see group selection being a good explanation 0:11:58.120 --> 0:12:00.840 for what animals are doing in the wild. So imagine 0:12:00.880 --> 0:12:04.200 you did have like a population of individuals who were 0:12:04.559 --> 0:12:08.240 very responsible rodents and were limiting themselves to two babies 0:12:08.280 --> 0:12:10.720 each because they didn't want to over exploit the seeds. 0:12:11.320 --> 0:12:14.520 And then you had a mutation in a gene, and 0:12:14.559 --> 0:12:20.440 a selfish gene popped up. Okay, and those parents six babies. 0:12:20.480 --> 0:12:23.880 The jerk rats had six babies, and there's all these 0:12:23.920 --> 0:12:27.000 extra seeds because everybody else is being responsible, and so 0:12:27.080 --> 0:12:29.720 all of their babies survive. And they also got the 0:12:29.840 --> 0:12:32.400 jerk gene, and so they have six babies too. 0:12:32.679 --> 0:12:34.040 Dominion of the jerk rats. 0:12:34.440 --> 0:12:37.520 Dominion of the jerk rats exactly. So over time, that 0:12:37.679 --> 0:12:41.439 selfish gene is going to pass through the population. You're 0:12:41.440 --> 0:12:42.800 going to end up with a lot more of this 0:12:42.920 --> 0:12:43.680 jerk gene. 0:12:43.840 --> 0:12:47.320 So does this argue against when Edward's idea of evolution 0:12:47.640 --> 0:12:48.800 at the population level. 0:12:49.040 --> 0:12:51.880 Yes, it does. And so just about whenever we look 0:12:52.360 --> 0:12:54.679 when we go out into nature, we see that animals 0:12:54.720 --> 0:12:56.680 are trying to have as many babies as they can, 0:12:56.800 --> 0:12:59.959 maybe not in a particular season, but across their entire lifetime. 0:13:00.480 --> 0:13:03.040 We don't see much evidence of individuals sort of doing 0:13:03.120 --> 0:13:05.360 things for the good of the species. Most of the 0:13:05.360 --> 0:13:07.000 evidence we find is that they're doing it for the 0:13:07.000 --> 0:13:10.760 good of themselves. And we think that's because selfish strategies 0:13:10.800 --> 0:13:14.880 could easily invade populations where everyone's you know, trying to 0:13:14.880 --> 0:13:16.560 do things for the good of the species. That's just 0:13:16.640 --> 0:13:20.400 a strategy that's very easy to invade by more selfish behaviors. 0:13:20.640 --> 0:13:24.000 This is a cool test because the cooperative strategy is 0:13:24.040 --> 0:13:27.960 actually more successful. Right, if nobody's a jerk, everybody does better. 0:13:28.280 --> 0:13:31.439 It's sort of a prisoner's dilemma situation. But if everybody 0:13:31.480 --> 0:13:34.720 else is cooperating and you're the jerk, then you individually 0:13:34.800 --> 0:13:37.680 win out and then your babies dominate the future. Yes, 0:13:37.880 --> 0:13:41.240 and so if you were operating at a population level, 0:13:41.440 --> 0:13:43.640 you would definitely choose no jerks. 0:13:43.920 --> 0:13:44.079 Yeah. 0:13:44.120 --> 0:13:44.320 Yeah. 0:13:44.320 --> 0:13:46.280 If selection was acting at the level of the group, 0:13:46.320 --> 0:13:48.360 then maybe that would be better for everybody, but we 0:13:48.400 --> 0:13:50.840 don't see evidence of that happening. And additionally, like even 0:13:50.840 --> 0:13:53.000 if you could get a group of individuals to be 0:13:53.160 --> 0:13:57.960 like super nice and everybody cooperates, usually we see migration 0:13:58.080 --> 0:14:01.640 between groups because they don't usually exist completely in isolation. 0:14:02.080 --> 0:14:04.599 So if you had a jerk group, you know, a 0:14:04.679 --> 0:14:08.240 little north of you, some jerks might move south and 0:14:08.280 --> 0:14:12.319 invade your population. And since you've left all these resources unexploited, 0:14:12.320 --> 0:14:14.400 they're going to come in and sort of mess everything 0:14:14.440 --> 0:14:15.520 up for everybody else. 0:14:15.840 --> 0:14:17.040 Those northern jerks. 0:14:17.080 --> 0:14:20.240 Every time time I know, I'm looking at you, Canada, 0:14:20.720 --> 0:14:24.200 I'm just kidding. Canadians are way nicer. We should have 0:14:24.200 --> 0:14:25.000 done it in reverse. 0:14:25.480 --> 0:14:27.080 Oh, now you're offending the Mexicans. 0:14:27.760 --> 0:14:30.400 Oh no, no, no, I meant it's the Americans ruining 0:14:30.440 --> 0:14:32.640 things for the Canadians, is what I was saying. No, no, no, no, 0:14:35.080 --> 0:14:38.000 don't get me wrong. Okay, So there are some arguments 0:14:38.000 --> 0:14:40.400 still that there could be some situations where it makes 0:14:40.440 --> 0:14:43.080 sense to think about selection from a group or a 0:14:43.120 --> 0:14:46.560 species level, But I think in general, we think that 0:14:46.960 --> 0:14:49.000 most of the time selection is happening at the level 0:14:49.040 --> 0:14:51.480 of the individual and that you can, you know, get 0:14:51.520 --> 0:14:53.720 away with not thinking about group selection most of the time. 0:14:53.840 --> 0:14:56.320 And this is true for behavior and also for more 0:14:56.360 --> 0:14:59.200 like mechanical traits like cheetah's running fast and stuff. 0:14:59.560 --> 0:15:03.160 Yes, okay, okay, And actually I bought a recent animal 0:15:03.160 --> 0:15:05.160 behavior textbook because that's what I learned in like the 0:15:05.240 --> 0:15:06.880 early two thousands, and I was like, I just want 0:15:06.880 --> 0:15:08.640 to be one hundred percent chore that this is what 0:15:08.680 --> 0:15:10.360 everybody still says and it is. 0:15:10.560 --> 0:15:13.280 So then you're telling me that you can't choose behavior 0:15:13.320 --> 0:15:15.880 based at the population level, like hey, everybody be nice 0:15:16.000 --> 0:15:19.360 or everybody like to have go to parties or whatever. 0:15:19.920 --> 0:15:22.560 And so in that case, how do we get things 0:15:22.640 --> 0:15:27.960 like altruism or social behavior if natural selection acts only 0:15:28.000 --> 0:15:28.920 on individuals. 0:15:29.120 --> 0:15:31.240 That's the puzzle, right, Yeah, that is the puzzle. Okay. 0:15:31.240 --> 0:15:33.560 So we're going to talk about three or four different 0:15:33.560 --> 0:15:36.200 ways that we think you can get it by individual 0:15:36.360 --> 0:15:39.880 level selection. Oh all right, So the first way is 0:15:39.880 --> 0:15:43.280 what we call kin selection. This is an idea by 0:15:43.280 --> 0:15:45.680 William Hamilton. It was proposed in the sixties, and the 0:15:45.760 --> 0:15:50.040 idea is that you've got genes for particular traits, and 0:15:50.560 --> 0:15:54.040 you can get those genes passed from one generation to 0:15:54.080 --> 0:15:58.600 another by having your own babies directly, but you can 0:15:58.720 --> 0:16:02.800 also increase the frequency of those genes by doing things 0:16:02.880 --> 0:16:06.960 like helping out your brother, and so that indirectly increases 0:16:07.000 --> 0:16:11.240 your fitness because you probably share about fifty percent of 0:16:11.280 --> 0:16:14.800 your genes by descent because you come from the same parents. 0:16:15.280 --> 0:16:17.760 And you know, for example, if you're a diploid organism, 0:16:17.760 --> 0:16:21.600 so humans are diploid organisms, that means we have two chromosomes. 0:16:21.880 --> 0:16:24.160 We got fifty percent of our genes from our mom, 0:16:24.200 --> 0:16:26.600 fifty percent of our genes from our dad, and just 0:16:26.680 --> 0:16:30.280 by random chance, you and a sibling probably share about 0:16:30.360 --> 0:16:33.160 fifty percent of the versions of the genes that you 0:16:33.280 --> 0:16:35.080 have in your body. Does that make sense? 0:16:35.600 --> 0:16:38.640 Yes, So basically, I have a big nose. My brother 0:16:38.720 --> 0:16:41.480 is a big nose. If I help my brother's kids, 0:16:41.560 --> 0:16:44.560 then I'm increasing the big nose fraction of future generation. 0:16:44.760 --> 0:16:47.840 So I'm not really being altruistic by helping people who 0:16:47.840 --> 0:16:49.840 are not my direct offspring. 0:16:49.840 --> 0:16:53.040 As long as they're related to you. Yeah, yes, right right, yeah, 0:16:53.040 --> 0:16:54.120 as long as they're related. 0:16:54.360 --> 0:16:55.760 That's why it's called kin selection. 0:16:55.880 --> 0:16:58.040 I guess, yes, exactly right, and so are there's some 0:16:58.120 --> 0:17:00.480 predictions that come from this. You should care about how 0:17:00.520 --> 0:17:03.800 closely related people are to you, and so for example, 0:17:03.800 --> 0:17:06.520 you should be more likely to help a brother or 0:17:06.560 --> 0:17:09.600 a sister, and you should be, you know, sort of 0:17:09.960 --> 0:17:13.040 willing to help like a half sibling or a cousin. 0:17:13.280 --> 0:17:14.520 Depends how big their nose is. 0:17:14.560 --> 0:17:20.560 Actually that's maybe, that's right. Depends on the gene. But 0:17:20.600 --> 0:17:22.840 you know, for example, if you imagine that there is 0:17:22.880 --> 0:17:27.040 a gene out there for altruism, and that gene does 0:17:27.080 --> 0:17:29.679 make you more likely to help out other members of 0:17:29.720 --> 0:17:32.640 your family, then you can imagine that that gene would 0:17:32.680 --> 0:17:36.120 pass through a population if family members are helping each other. 0:17:36.600 --> 0:17:40.080 And so there's this fameless quote by a scientist named 0:17:40.200 --> 0:17:43.159 JBS Haldane and he was asked, would you save a 0:17:43.240 --> 0:17:46.040 drowning brother if it risked your own life? And he 0:17:46.080 --> 0:17:49.840 said no, but I would save two brothers or eight 0:17:49.920 --> 0:17:52.080 cousins because. 0:17:53.560 --> 0:17:55.000 And mathematically that checks out. 0:17:55.200 --> 0:17:57.000 That's right, that's right. And so whether or not you 0:17:57.040 --> 0:17:59.479 should engage in a behavior that helps out your family 0:17:59.480 --> 0:18:02.800 members to some extent depends on how closely related they 0:18:02.840 --> 0:18:05.240 are to you. How much the cost would be to 0:18:05.280 --> 0:18:08.679 yourself and how much they would benefit. And so you 0:18:08.680 --> 0:18:12.439 should expect to see altruistic behaviors arising a mon closely 0:18:12.440 --> 0:18:15.520 related individuals if it's going to result in, for example, 0:18:15.560 --> 0:18:18.439 your siblings having more kids that are going to carry 0:18:18.440 --> 0:18:20.240 some of the genes that you would find in yourself. 0:18:20.560 --> 0:18:23.480 And so maybe you're not having as many kids personally, 0:18:23.920 --> 0:18:26.520 but if your siblings are having loads of additional kids, 0:18:26.560 --> 0:18:29.480 then your genes are still getting out there, and so indirectly, 0:18:29.920 --> 0:18:32.440 your fitness is doing great, and so maybe we see 0:18:32.440 --> 0:18:37.040 altruism happening because selfishly, that still helps your genes pass 0:18:37.520 --> 0:18:38.640 through the environment. 0:18:38.760 --> 0:18:40.639 All right, So just to make sure I understand, we 0:18:40.680 --> 0:18:43.800 started out wondering why would anybody die for other members 0:18:43.800 --> 0:18:45.879 of the population, And this seems like to me a 0:18:45.920 --> 0:18:48.840 partial answer, because it doesn't suggest you would die for 0:18:48.920 --> 0:18:51.320 any member of the population, but it tells you that 0:18:51.400 --> 0:18:55.000 you might sacrifice yourself for people you're related to who 0:18:55.040 --> 0:18:58.280 are not directly your offspring. Yes, exactly, And that to 0:18:58.320 --> 0:19:01.239 me described as sort of like limited local altruism that 0:19:01.280 --> 0:19:03.320 like falls off with the size of the nose of 0:19:03.359 --> 0:19:06.760 people in your family. But then you added this twist 0:19:06.800 --> 0:19:10.800 about a gene for altruism itself, right, because this doesn't 0:19:10.800 --> 0:19:13.800 require a gene for altruism. You just support people who 0:19:13.960 --> 0:19:15.960 have enough genes that overlap with you. 0:19:16.560 --> 0:19:19.960 Yes, but you could imagine that a gene for altruism 0:19:19.960 --> 0:19:22.880 would be how you get this trait to pass from 0:19:22.920 --> 0:19:25.080 family member to family member to family member. 0:19:25.240 --> 0:19:27.879 Oh, I see, yeah, The gene for altruism helps you 0:19:27.960 --> 0:19:29.480 recognize that this is beneficial. 0:19:29.840 --> 0:19:32.960 It helps make sure that the trait passes in families 0:19:33.000 --> 0:19:33.879 and is maintained. 0:19:34.680 --> 0:19:35.960 I see, all right. 0:19:35.960 --> 0:19:38.160 And we have some examples of this. So, for example, 0:19:38.440 --> 0:19:42.400 there are these squirrels that you find in California building's 0:19:42.440 --> 0:19:45.720 ground squirrels, and the females tend to stay in the 0:19:45.760 --> 0:19:47.919 areas where they were born, whereas the males tend to 0:19:47.960 --> 0:19:51.280 go away. And so if you're a female, your sisters 0:19:51.280 --> 0:19:53.520 are likely to be nearby, your aunts are likely to 0:19:53.520 --> 0:19:56.320 be nearby. And what they find is that the females 0:19:56.359 --> 0:19:58.960 are more likely to call when there's a predator around. 0:19:59.040 --> 0:20:01.600 And so when a predator's around, they call, and then 0:20:01.680 --> 0:20:04.600 their sisters and their aunts, maybe their mom and even 0:20:04.640 --> 0:20:07.960 their kids go and hide in their burrows. But when 0:20:07.960 --> 0:20:11.000 you call, you also increase the probability that the coyote 0:20:11.040 --> 0:20:14.000 goes after you because you've drawn its attention. So it's 0:20:14.000 --> 0:20:16.840 a risky behavior that has a cost. But they've also 0:20:16.960 --> 0:20:19.960 found that females will call even if none of their 0:20:19.960 --> 0:20:22.439 own kids are around, so it's not just a direct 0:20:22.480 --> 0:20:26.120 fitness thing. They will call to help their aunts get 0:20:26.160 --> 0:20:28.200 out of the way or some or their sisters get 0:20:28.240 --> 0:20:29.600 out of the way. So it looks like they're also 0:20:29.640 --> 0:20:32.840 willing to take a cost to get an indirect fitness benefit, 0:20:32.920 --> 0:20:34.439 so to help their sisters and stuff. 0:20:34.960 --> 0:20:38.840