WEBVTT - Where’s my eternal youth? Part 2 0:00:03.000 --> 0:00:05.880 Welcome to Stuff to Blow your Mind from how Stuff 0:00:05.880 --> 0:00:14.320 Works dot com. Hey you welcome to Stuff to Blow 0:00:14.400 --> 0:00:17.240 your Mind. My name is Robert Lamb and I'm Joe McCormick, 0:00:17.280 --> 0:00:19.960 and we're back for part two of our discussion about 0:00:20.000 --> 0:00:23.239 where's my eternal youth? Why can't I be young and 0:00:23.280 --> 0:00:27.040 beautiful forever? Why do we age? I know that's the 0:00:27.120 --> 0:00:29.800 It's the question we've always wondered. It shows up in 0:00:29.800 --> 0:00:35.840 our philosophical writings, it shows up in our religion, our mythology. Uh. 0:00:36.120 --> 0:00:39.280 In researching this topic, I kept thinking back to Genesis 0:00:39.320 --> 0:00:42.320 six three. This is the King James version, and the 0:00:42.400 --> 0:00:45.479 Lord said, my spirit shall not always strive with man, 0:00:45.960 --> 0:00:49.680 for that he is also flesh. Yet his days shall 0:00:49.760 --> 0:00:54.520 be a hundred and twenty years. So there's God putting 0:00:55.000 --> 0:00:58.800 a limit on how old a human can become and 0:00:58.880 --> 0:01:02.480 saying like, here's the aging process. Uh, these are the rules. 0:01:02.640 --> 0:01:05.640 Obviously doesn't apply to Highlanders, that's right. Well, you know, 0:01:06.200 --> 0:01:08.200 maybe they're they're part of the giants in the earth 0:01:08.319 --> 0:01:10.039 or something. I don't know, Oh that could be. Yeah, 0:01:10.040 --> 0:01:13.440 I guess they're not humans. So well, the spoiler for 0:01:13.520 --> 0:01:18.039 Highlander too certain cuts they are not from Earth in 0:01:18.080 --> 0:01:20.840 the good cuts. They're not from Earth yet again, we're 0:01:20.840 --> 0:01:23.720 just trying to throw those seeds down. Highlander two episode 0:01:23.760 --> 0:01:26.640 it's coming now. Speaking of parts one and two, this 0:01:26.720 --> 0:01:29.319 episode is a part two. Yeah, so if you haven't 0:01:29.360 --> 0:01:31.039 listened to part one yet, you should go back check 0:01:31.080 --> 0:01:34.280 that out first. And that we explored the question of 0:01:34.360 --> 0:01:37.760 why we age. We look at some animals that don't 0:01:37.800 --> 0:01:40.360 really age in the same way that humans and other 0:01:40.400 --> 0:01:45.600 similar mammals do, and we look at historical explanations people 0:01:45.640 --> 0:01:48.320 have tried to come up with for why we age, 0:01:48.680 --> 0:01:51.200 and we also explored some reasons to think that those 0:01:51.240 --> 0:01:54.120 historical explanations were not correct. Today, we're going to try 0:01:54.120 --> 0:01:59.560 to get into the modern evolutionary synthesis take on why 0:01:59.720 --> 0:02:02.440 we age. What's happening and how do you solve this 0:02:02.560 --> 0:02:06.680 paradox of the fact that aging is a decline over 0:02:06.760 --> 0:02:11.600 time in our survival and reproduction fitness, and yet evolution 0:02:11.639 --> 0:02:15.840 should be constantly optimizing our survival and reproduction fitness. Why 0:02:15.840 --> 0:02:18.400 would it allow us to go into this period where 0:02:18.440 --> 0:02:21.520 we tend to die and tend to get worse at 0:02:21.520 --> 0:02:25.320 surviving and tend to not be able to reproduce anymore. Indeed, 0:02:25.360 --> 0:02:29.240 because I certainly don't want to deify natural selection and 0:02:29.280 --> 0:02:34.200 say that like natural selection produces perfect forms or ideal forms. 0:02:34.240 --> 0:02:36.840 But look at the forms that natural selection has produced, 0:02:37.040 --> 0:02:41.640 look at all the various engineering problems that that that 0:02:41.720 --> 0:02:44.600 evolution has managed to solve. Why would there be this 0:02:44.880 --> 0:02:48.560 be this huge, at least from our perspective, flaw in 0:02:48.600 --> 0:02:51.200 the design. Yeah. Now, of course, today, as we often 0:02:51.200 --> 0:02:54.079 do with evolution, just for the ease of communication, we're 0:02:54.080 --> 0:02:56.320 going to be using a lot of metaphors that offer 0:02:56.360 --> 0:02:59.960 a kind of like embodied view of evolution, as if 0:03:00.080 --> 0:03:02.760 like it's making choices. What we, of course know is 0:03:02.800 --> 0:03:07.280 that evolution is a is an optimization algorithm. It's not 0:03:07.360 --> 0:03:09.680 a person, it's not a thing. It doesn't really have 0:03:09.840 --> 0:03:12.560 desires of it of its own. It has a way 0:03:12.600 --> 0:03:15.240 that it works, and the way that it works is 0:03:15.280 --> 0:03:19.919 to optimize the success of genes that survived natural selection 0:03:19.960 --> 0:03:22.800 and reproduce. Now, one of the answers we explored in 0:03:22.840 --> 0:03:26.640 the last episode is one of the most common things 0:03:26.639 --> 0:03:28.560 people are going to turn to when they're trying to 0:03:28.600 --> 0:03:31.320 explain why we age. It's the thing that my brain 0:03:31.400 --> 0:03:35.000 and immediately went to before I read anything on this subject, 0:03:35.480 --> 0:03:39.040 I started to think, well, let's see, if everybody just 0:03:39.200 --> 0:03:44.800 lived forever and nobody naturally aged out and died, then 0:03:44.920 --> 0:03:48.280 you'd have way too much competition for resources, right, You'd 0:03:48.320 --> 0:03:51.200 have way too many people trying to live on the 0:03:51.240 --> 0:03:53.600 same landscape. You'd have too many people trying to eat 0:03:53.680 --> 0:03:57.160 from the same food sources. You'd have overpopulation, and and 0:03:57.200 --> 0:04:00.120 everybody would suffer for it. Overpopulation ties and to a 0:04:00.200 --> 0:04:02.880 number of our different dystopian views of the future, as 0:04:03.040 --> 0:04:07.120 does the possibility of immortality becoming an option at least 0:04:07.120 --> 0:04:09.840 a certain privileged people in society. You know, you get 0:04:09.880 --> 0:04:14.960 this sort of trope of the awful uh Methuselah of 0:04:15.000 --> 0:04:19.880 the future, Right, some just dreary, old, greedy individual who 0:04:20.080 --> 0:04:23.159 will not die and let go the reigns of life 0:04:23.440 --> 0:04:25.720 so that others may grasp it. Right, Well, as much 0:04:25.760 --> 0:04:28.360 as we don't personally want to grow old and die, 0:04:28.680 --> 0:04:31.520 you can sort of recognize from an impartial standpoint, if 0:04:31.520 --> 0:04:34.080 you just consider it in other people, that it seems 0:04:34.120 --> 0:04:37.640 kind of unfair that people should live forever, right, Yeah, yeah, 0:04:37.720 --> 0:04:41.040 unless it's me or someone that I'm investing, and there 0:04:41.160 --> 0:04:43.520 they should put a limit on that stuff. Yeah, So 0:04:43.640 --> 0:04:46.960 but these types of answers, while true, it is true 0:04:47.040 --> 0:04:49.840 that it's good for the species that we should age 0:04:49.839 --> 0:04:53.559 and die, and that it's good for future generations. Uh, 0:04:53.760 --> 0:04:56.320 good of the species and good of the group based 0:04:56.360 --> 0:05:00.800 explanations come under a lot of fire from evolutionary biologists. 0:05:01.400 --> 0:05:05.000 There's some biologists to endorse kind of qualified versions of 0:05:05.000 --> 0:05:07.080 of good of the group and good of the species 0:05:07.440 --> 0:05:10.400 type explanations, but there I think many more who don't. 0:05:10.839 --> 0:05:13.400 And here's an example to illustrate one of the big 0:05:13.480 --> 0:05:17.279 problems in why these good of the group explanations failed 0:05:17.320 --> 0:05:20.479 to hold up. Alright, hit me with it. Okay. Let's 0:05:20.480 --> 0:05:23.640 imagine a pack of alien space wolves. Okay, and for 0:05:23.720 --> 0:05:27.119 our Warhammer for fans out there, he's not talking about 0:05:27.120 --> 0:05:29.280 space marines here. Wait, I don't know what space will 0:05:29.680 --> 0:05:31.720 Is that a thing? Yeah, it's a faction of the 0:05:31.760 --> 0:05:36.160 space marines in the Warhammer forty K universe that are wolves. 0:05:36.520 --> 0:05:39.479 Well no, they well they wear wolf skins and they're 0:05:39.920 --> 0:05:43.280 you know, genetically enhanced super soldiers. Okay, So it would 0:05:43.320 --> 0:05:46.800 really complicate them the analogy you're making here, if if 0:05:46.839 --> 0:05:49.000 we were to draw them into the discussion. Well, I 0:05:49.040 --> 0:05:51.280 was just trying to make clear that this is a hypothetical, 0:05:51.440 --> 0:05:54.080 not like real wolves on Earth. Okay, so alien space 0:05:54.120 --> 0:05:57.719 wolves living on an asteroid somewhere in hunting space here. Now, 0:05:57.800 --> 0:06:00.920 let's imagine this pack of alien space wolves has evolved 0:06:00.960 --> 0:06:03.599 genes that cause them to grow old and become infertile 0:06:03.680 --> 0:06:06.320 after about ten years of age, after which you know 0:06:06.360 --> 0:06:09.760 they usually die within a couple of years. And let's 0:06:09.760 --> 0:06:13.000 say that each female space wolf has an average of 0:06:13.120 --> 0:06:17.160 one space wolf pup every year that she remains fertile. 0:06:17.600 --> 0:06:20.800 So unless the space wolf is killed by injury or 0:06:20.920 --> 0:06:25.440 disease or a marauding space explorer, um, the average space 0:06:25.480 --> 0:06:30.560 wolf female has tin offspring in her life lifespan. Everybody's happy, right, 0:06:30.600 --> 0:06:32.720 because they don't eat too many of the space dear, 0:06:32.760 --> 0:06:36.400 they don't become overpopulated. It just works out pretty well. 0:06:36.920 --> 0:06:41.200 But then suddenly one of these space wolves acquires a 0:06:41.279 --> 0:06:44.719 mutation that allows her to stay fertile and survive for 0:06:44.839 --> 0:06:49.599 twelve years instead of ten, So she has twelve of 0:06:49.720 --> 0:06:52.800 space wolf pups, whereas all the other females in the 0:06:52.839 --> 0:06:56.080 pack are still having ten, and half of her pups 0:06:56.120 --> 0:07:00.200 carried this extended fertility and longevity gene, So those x 0:07:00.240 --> 0:07:03.919 pups each have twelve pups, while non carriers of the 0:07:03.960 --> 0:07:06.480 gene only have ten, and so on and so on 0:07:06.600 --> 0:07:11.000 down the generations, and eventually this cheater gene for extended 0:07:11.080 --> 0:07:15.120 life and extended fertility is going to proliferate, even if 0:07:15.160 --> 0:07:18.120 it might be worse off for everybody in the long run. 0:07:18.200 --> 0:07:21.760 Even if the long living, long reproducing animals have too 0:07:21.760 --> 0:07:25.600 many offspring and consume too many resources and suffer die outs, 0:07:25.640 --> 0:07:30.200 this won't really cause a reselection towards shorter lifespans, because 0:07:30.560 --> 0:07:33.960 how would it. Instead, what it would do is optimize 0:07:34.000 --> 0:07:37.040 for whatever genes are possessed by the survivors of those 0:07:37.120 --> 0:07:39.840 die outs, and that would probably be like those that 0:07:40.040 --> 0:07:43.920 store fat better, or hunt better, or can extract nutrition 0:07:44.000 --> 0:07:46.760 from space moss in addition to meat. And this is 0:07:46.760 --> 0:07:49.600 a really common type of argument against good of the 0:07:49.640 --> 0:07:52.960 group and good of the species explanations and evolution, because 0:07:53.080 --> 0:07:57.600 any mutation that cheats on the stasis you've created for 0:07:57.640 --> 0:07:59.880 the good of the group will tend to start to 0:08:00.000 --> 0:08:03.400 at an edge and then have more offspring than those 0:08:03.440 --> 0:08:06.560 who don't cheat, and eventually that new gene will become 0:08:06.600 --> 0:08:08.600 the norm. Right, Yeah, It's kind of like if you 0:08:08.680 --> 0:08:12.119 have a you know, an academic environment where everybody's cheating 0:08:12.120 --> 0:08:15.240 on the exam. Need the grading becomes that much harder 0:08:15.280 --> 0:08:18.840 each and every time. It's true. Yeah, it's great. So 0:08:18.920 --> 0:08:21.280 it's like you got a grade on a curve because 0:08:21.280 --> 0:08:25.680 everybody's cheating, so everybody's grade goes down. Um. Yeah, And 0:08:25.760 --> 0:08:28.800 so I just want to remind you, though, this doesn't 0:08:28.840 --> 0:08:31.000 mean that there is not such a thing as the 0:08:31.040 --> 0:08:32.640 good of the group and the good of the species. 0:08:32.679 --> 0:08:35.520 Those things clearly are true. And it clearly is true 0:08:35.640 --> 0:08:39.000 that it's good for the next generation that older generations 0:08:39.080 --> 0:08:41.880 age out and die. I care about the survival of 0:08:41.920 --> 0:08:44.400 the rest of my group. I care about members of 0:08:44.400 --> 0:08:47.640 my species and about future generations. But I care because 0:08:47.640 --> 0:08:50.800 I have a brain and I can recognize what's going on. 0:08:51.240 --> 0:08:54.320 Magines don't care, and your genes don't care. They just 0:08:54.440 --> 0:08:59.000 chemically proliferate themselves. They don't have a sentimental attachment or 0:08:59.120 --> 0:09:02.480 or an idea that the next generation should get resources 0:09:02.520 --> 0:09:04.560 to all right, So this just brings us back to 0:09:04.640 --> 0:09:09.640 the question, though, why have we evolved to grow old? Right? 0:09:09.679 --> 0:09:13.439 It's still unsolved. Why not live and reproduce forever, maintaining 0:09:13.520 --> 0:09:17.880 perfect youth and vigor until something extrinsic happens, until we 0:09:17.920 --> 0:09:21.800 get killed by a hemorrhagic fever or tractor accident. Alright, 0:09:21.800 --> 0:09:23.440 we're gonna take a quick break and we come back. 0:09:23.559 --> 0:09:29.400 We will answer that very question. Thank alright, we're back. 0:09:29.520 --> 0:09:31.960 Al right. So, there are a number of modern, well 0:09:32.000 --> 0:09:36.080 accepted scientific theories trying to answer the question of why 0:09:36.240 --> 0:09:39.760 we evolved to age. And here's a starting point for 0:09:39.800 --> 0:09:42.040 several of those theories. Let's go back to the wolves 0:09:42.080 --> 0:09:45.720 for a second. Imagine the space wolves. Maybe a hypothetical 0:09:45.760 --> 0:09:48.560 wolf species could breed and stay healthy until about the 0:09:48.600 --> 0:09:51.920 age of ten. Like we said, why not twenty, Why 0:09:51.960 --> 0:09:55.520 not thirty? Why not five hundred? Well, here are a 0:09:55.559 --> 0:09:59.840 few things to consider. Wolves did not evolve in zoo 0:10:00.120 --> 0:10:04.320 's or as domestic pets, where they're guaranteed meals and 0:10:04.360 --> 0:10:09.240 protection from violence and guaranteed access to veterinary care. The 0:10:09.360 --> 0:10:13.240 landscape that created the wolf as it exists is one 0:10:13.240 --> 0:10:16.320 in which there is a constant struggle to get enough 0:10:16.360 --> 0:10:19.640 meat to survive and to not get sick and die, 0:10:19.720 --> 0:10:22.400 and to not get injured and become unable to hunt, 0:10:22.440 --> 0:10:25.160 so you starve. If you are a wolf living in 0:10:25.160 --> 0:10:28.079 the wild, and you survive the first year of your life, 0:10:28.280 --> 0:10:32.200 one of these things like injury or disease or starvation 0:10:32.960 --> 0:10:36.760 very likely will kill you before you get a chance 0:10:36.800 --> 0:10:40.319 to reach old age. These causes of death like disease 0:10:40.320 --> 0:10:43.840 and injury, or what's known as quote extrinsic causes of death, 0:10:43.920 --> 0:10:47.200 death caused by outside pressures and not by stuff that's 0:10:47.200 --> 0:10:50.200 in your genes or by old age. And so we 0:10:50.240 --> 0:10:52.439 can look at the real life example to see how 0:10:52.440 --> 0:10:55.800 common this is. The actual gray wolf Canis lupus lives 0:10:55.840 --> 0:10:58.520 somewhere around an average of six years or so in 0:10:58.559 --> 0:11:01.319 the wild, but in captivity it can live for more 0:11:01.360 --> 0:11:05.680 than fifteen years. So here's the first crucial bit to 0:11:05.840 --> 0:11:09.280 use some more metaphorical language. If there are physical processes 0:11:09.320 --> 0:11:13.840 that tend to render a wolf progressively less fit every 0:11:13.960 --> 0:11:18.120 month after it's more than ten years old, evolution almost 0:11:18.200 --> 0:11:22.120 never sees that. To put it in another metaphor, asking 0:11:22.160 --> 0:11:25.640 why evolution allows the wolf to grow old to deteriorate 0:11:25.640 --> 0:11:28.360 with old age is kind of like asking why we 0:11:28.480 --> 0:11:32.600 don't have laws against time travel. The reason isn't that 0:11:32.640 --> 0:11:36.040 our legislative bodies have considered and debated the issue of 0:11:36.120 --> 0:11:38.640 time travel and in the end they concluded that time 0:11:38.640 --> 0:11:41.800 travel is good, we better, we better allow it. That's 0:11:41.840 --> 0:11:45.880 not what happens. What happens is the issue doesn't come up. Yeah, 0:11:45.920 --> 0:11:48.960 it reminds me of some of these various programs that 0:11:49.720 --> 0:11:52.200 informs you have to do to figure out how you're 0:11:52.240 --> 0:11:55.080 saving your for your retirement, and they tend not to 0:11:55.160 --> 0:11:58.600 cover the second century of your life because it's not 0:11:58.679 --> 0:12:02.199 going to happen. That's perfect metaphor. Yeah, how come you're 0:12:02.240 --> 0:12:05.400 not saving enough money for when you're two hundred years old. 0:12:05.800 --> 0:12:08.120 It's not that you've decided it's better to be broke 0:12:08.200 --> 0:12:12.079 when you're two hundred. It's just that the the situation 0:12:12.160 --> 0:12:14.520 of being two hundred does not tend to come up 0:12:14.640 --> 0:12:18.880 very often. Now, obviously it's not nearly that extreme because sometimes, 0:12:18.920 --> 0:12:21.600 in some cases animals do live to old age and 0:12:21.640 --> 0:12:25.680 they face biological sinescence under natural conditions. But for many 0:12:25.760 --> 0:12:29.560 species it's pretty rare. For species of animals that tend 0:12:29.640 --> 0:12:32.840 to die from one cause or another before they get 0:12:32.880 --> 0:12:36.840 the chance to grow old evolution doesn't have many opportunities 0:12:37.120 --> 0:12:40.960 to test what happens in old age, so it can't 0:12:40.960 --> 0:12:45.320 optimize the animal for old age very efficiently, and compare 0:12:45.360 --> 0:12:48.440 this to how strongly evolution tests and optimizes for the 0:12:48.480 --> 0:12:52.199 effects of genes that manifest in early life. If something 0:12:52.240 --> 0:12:56.160 affects how likely you are to survive at age twenty 0:12:56.320 --> 0:12:59.920 or at age ten, evolution is going to be very strong, 0:13:00.040 --> 0:13:04.120 only selecting four or against that gene. Okay, So this 0:13:04.200 --> 0:13:06.920 is one part of the landscape of explanations today. Most 0:13:06.960 --> 0:13:11.160 species that show significant aging evolved to their anatomically modern 0:13:11.200 --> 0:13:14.880 condition in a situation where mortality was high and evolution 0:13:14.960 --> 0:13:17.800 didn't get a lot of opportunities to see what happens 0:13:17.800 --> 0:13:21.120 in old age, much less optimize it. Uh, let's introduce 0:13:21.120 --> 0:13:24.079 another wrinkle into the explanation. Yeah, this one has a 0:13:24.080 --> 0:13:28.600 wonderful title. This is mutation accumulation. Right, So we go 0:13:28.679 --> 0:13:32.320 to the British biologist Peter B. Meadair. He was one 0:13:32.320 --> 0:13:35.320 of the primary evolutionary thinkers credited with working out the 0:13:35.360 --> 0:13:38.480 implications of this model of aging, where the force of 0:13:38.520 --> 0:13:42.880 selection just declines with old age. So in several works 0:13:42.880 --> 0:13:45.800 in the middle of the nineteen forties and the nineteen fifties, 0:13:46.280 --> 0:13:49.920 UH he argued, based on similar logic, that natural selection 0:13:49.960 --> 0:13:52.840 would often be blind to the effects of mutations that 0:13:52.880 --> 0:13:57.559 cause negative effects laid in life after reproduction is mostly stopped. 0:13:57.559 --> 0:14:01.120 So let's use another analogy. Imagine a mutation called the 0:14:01.160 --> 0:14:05.600 twenty birthday surprise gene, which means that on the day 0:14:05.679 --> 0:14:09.360 you turn twenty, carriers of this gene suddenly transform into 0:14:09.400 --> 0:14:12.320 a bucket of fish heads and thus lose all ability 0:14:12.360 --> 0:14:16.080 to reproduce. Now, this would mean that in order to 0:14:16.160 --> 0:14:19.520 pass on this gene, a carrier would have to reproduce 0:14:19.680 --> 0:14:23.120 before their twentieth birthday, So kids they have before they're 0:14:23.160 --> 0:14:26.680 twenty years old could still carry this gene, but they 0:14:26.720 --> 0:14:29.160 don't get the chance to have any kids after their 0:14:29.200 --> 0:14:31.480 twenty years old, when plenty of other members of the 0:14:31.480 --> 0:14:35.680 species would continue having children, All potential reproduction after twenty 0:14:35.800 --> 0:14:39.400 is canceled, thus giving people with this gene significantly fewer 0:14:39.480 --> 0:14:41.920 children on average than people without it, and so the 0:14:41.960 --> 0:14:46.080 gene is unlikely to spread in the population. Now imagine 0:14:46.120 --> 0:14:49.680 a similar gene. This is the hundredth birthday surprise gene. 0:14:50.360 --> 0:14:53.440 Carriers of this gene, upon the day of their hundredth 0:14:53.440 --> 0:14:57.000 birthday suddenly transform into a VHS copy of Highlander to 0:14:57.080 --> 0:15:00.440 the quickening okay, and and and therefore becoming more No, 0:15:00.640 --> 0:15:03.680 not quite No. The problem is, well, I guess you 0:15:03.680 --> 0:15:06.640 you might get to live somewhat forever on a shelf, 0:15:06.640 --> 0:15:09.720 but you don't. You definitely don't get to reproduce after that. Right, 0:15:09.760 --> 0:15:13.480 there's very little sexual reproduction between copies of Highlander to 0:15:13.640 --> 0:15:18.200 the quickening. But also it doesn't really matter, right because 0:15:18.240 --> 0:15:21.440 do carriers of this gene have any fewer children the 0:15:21.600 --> 0:15:24.880 non carriers of this gene? The answer is no, right, 0:15:24.920 --> 0:15:29.960 because who's still having children at age one hundred? Almost nobody. 0:15:30.040 --> 0:15:32.520 So even if you have this very unhelpful gene, you 0:15:32.560 --> 0:15:35.440 don't like it that you transform into a VHS tape 0:15:35.440 --> 0:15:38.280 on your hundredth birthday, that's not good for you. But 0:15:38.360 --> 0:15:40.920 it doesn't matter to how many children you have. It 0:15:40.960 --> 0:15:43.840 has no effect on that. So if you have this gene, 0:15:43.880 --> 0:15:46.440 you can spread it to all your children, and they 0:15:46.440 --> 0:15:49.560 can spread it to all of their children and so, 0:15:49.720 --> 0:15:52.120 and they'll all have just as many kids and grandkids 0:15:52.120 --> 0:15:54.440 as the neighbors who don't have it. You've already passed 0:15:54.480 --> 0:15:58.440 it on by the time it matters, So this would 0:15:58.440 --> 0:16:01.080 be the case. Though we we've we've used the Highlander 0:16:01.240 --> 0:16:04.640 to transformation as as an example here, but even if 0:16:04.680 --> 0:16:09.320 it were something seemingly beneficial, like say a gene made 0:16:09.320 --> 0:16:13.040 you suddenly really excellent and talking to members of the 0:16:13.040 --> 0:16:17.440 opposite sex at age one hundred, you know, like or 0:16:17.480 --> 0:16:20.560 the opposite it made you terrible at a speaking to 0:16:20.600 --> 0:16:23.840 the opposite sex at age one hundred, it would still 0:16:23.880 --> 0:16:27.040 be the same case, right, yeah, unless the basically the 0:16:27.040 --> 0:16:29.040 only thing that would matter would be if it's a 0:16:29.120 --> 0:16:32.560 gene that suddenly makes you able to reproduce again. I mean, 0:16:32.600 --> 0:16:35.160 if it did that, then that would probably matter. But 0:16:35.280 --> 0:16:38.320 as long as you're past the age of reproduction and 0:16:38.400 --> 0:16:43.120 you're not having any more children, mutations good or bad 0:16:43.280 --> 0:16:47.560 are just going to sort of accumulate randomly without having 0:16:47.640 --> 0:16:51.520 any effect Onesoever, natural selection just doesn't pay attention to 0:16:51.560 --> 0:16:54.400 them because it never gets to notice them. Well. But 0:16:54.400 --> 0:16:56.000 but then the other thing too, is that if you're 0:16:56.000 --> 0:16:57.800 talking about something that would kick in so late in 0:16:57.920 --> 0:17:02.080 life that even people with that gene might never experience it. Right. 0:17:02.160 --> 0:17:04.960 It's like if you're playing a role playing game, video 0:17:05.000 --> 0:17:06.760 game or what have you, and there's some sort of 0:17:06.760 --> 0:17:09.320 like high level ability and you look at it. It It 0:17:09.400 --> 0:17:11.000 looks great, but you know you're never going to play 0:17:11.040 --> 0:17:13.600 the game long enough to get it. Yeah, so what's 0:17:13.640 --> 0:17:16.160 the point. Yeah, the game might as well for you 0:17:16.400 --> 0:17:20.119 not even have that thing in it. And apparently there 0:17:20.160 --> 0:17:22.560 are going to be genetic mutations like that. And this 0:17:22.680 --> 0:17:24.959 was Meta Wars insight. It came to be known, as 0:17:25.040 --> 0:17:30.159 you said, as the mutation accumulation hypothesis. Whether reproduction stops 0:17:30.240 --> 0:17:33.160 because you die of extrinsic causes. This was a big 0:17:33.160 --> 0:17:35.040 thing Meta where had in mind. It's like we talked about, 0:17:35.080 --> 0:17:37.600 you know, the wolf gets injured and can't hunt, the 0:17:37.640 --> 0:17:40.960 wolf gets sick and dies, the wolf gets killed by something, 0:17:41.560 --> 0:17:44.720 whether that happens or because you age out of your 0:17:44.760 --> 0:17:48.639 reproductive stage of life for some other biological reasons. Genes 0:17:48.680 --> 0:17:52.840 that have negative effects that show up mostly after reproduction 0:17:52.920 --> 0:17:56.040 has stopped are not subject to the full force of 0:17:56.119 --> 0:17:59.600 natural selection. So there's not much preventing the proliferation of 0:17:59.680 --> 0:18:02.440 gene that harm you in old age because there's nothing 0:18:02.440 --> 0:18:05.240 to weed them out, and they accumulate in the genome 0:18:05.320 --> 0:18:08.560 over generations by what's known as genetic drift. And the 0:18:08.640 --> 0:18:12.480 genetic drift is just the random dispersing of genes that 0:18:12.560 --> 0:18:15.880 don't appear to have a very strong positive or negative effect. 0:18:16.280 --> 0:18:19.119 So if you've got a mutation that you acquire for 0:18:19.280 --> 0:18:22.480 a nasty surprise in old age, something bad that happens 0:18:22.520 --> 0:18:24.680 to your body. And you could look at the process 0:18:24.720 --> 0:18:27.840 of aging like this. It's just a large plethora of 0:18:27.920 --> 0:18:31.760 genetic mutations that cause bad things to happen to your body. 0:18:31.880 --> 0:18:34.720 Later on, you can still pass it on to your kids, 0:18:34.800 --> 0:18:37.400 because you're you've had all your kids by the time 0:18:37.440 --> 0:18:40.720 it starts affecting you. And so these genes can become 0:18:40.760 --> 0:18:43.680 common in the gene pool of your species simply because 0:18:43.760 --> 0:18:46.800 there's nothing stopping them. So simply put it in. The 0:18:46.840 --> 0:18:50.640 force of selection declines with age. Mutations that are neutral 0:18:50.760 --> 0:18:54.400 early in life when selection is strong, but negative later on, 0:18:55.080 --> 0:18:58.000 they could accumulate in the population. I like to think 0:18:58.000 --> 0:19:00.280 of this as the sack of kitty litter school things 0:19:00.280 --> 0:19:04.000 in the closet scenario. What, okay, explain, but a friend 0:19:04.040 --> 0:19:06.560 of mine, when I first met her, she had a 0:19:07.560 --> 0:19:09.760 cat box, and then she would scoop the cat box 0:19:09.800 --> 0:19:13.040 and it would accumulate in a garbage bag in the closet. 0:19:13.560 --> 0:19:16.440 Accumulate me, you mean accumulate as and she would dump 0:19:16.440 --> 0:19:18.399 it in a garbage bag in the close and it 0:19:18.440 --> 0:19:20.720 was it was a lot cleaner than this makes it sound, 0:19:20.760 --> 0:19:22.280 but it was. It was very much a sort of 0:19:22.359 --> 0:19:25.159 kicking the can down a road scenario, like eventually you're 0:19:25.200 --> 0:19:28.199 gonna have to take that bag of of of of 0:19:28.240 --> 0:19:32.919 litter scoopings out, but you're not. The whole situation is 0:19:32.960 --> 0:19:35.120 not built on what you're going to have to do tomorrow. 0:19:35.160 --> 0:19:37.640 It's about what's happening to today. But what if you're 0:19:37.640 --> 0:19:39.520 looking at that closet and you're saying, Oh, there's enough 0:19:39.560 --> 0:19:41.640 space in here that I could keep scooping it into 0:19:41.680 --> 0:19:44.000 the closet until I die of some of their cause, 0:19:44.480 --> 0:19:46.360 and then I would never have to take it out. 0:19:46.400 --> 0:19:49.760 It would be completely irrelevant. So it can accumulate forever, 0:19:49.920 --> 0:19:53.560 just like these deleterious Janes can. Okay, So that's clearly 0:19:53.640 --> 0:19:56.760 one part of the answer. One part is that stuff 0:19:56.800 --> 0:19:59.200 that affects you late in life is just less likely 0:19:59.280 --> 0:20:02.040 to get weeded out by natural selection. But what if 0:20:02.040 --> 0:20:05.879 there's something more than that. What if maladaptive genes that 0:20:05.960 --> 0:20:09.199 manifest in old age aren't just allowed to roam wild 0:20:09.320 --> 0:20:12.600 by sort of the careless shepherd of natural selection. What 0:20:12.680 --> 0:20:17.200 if they're positively selected for in some way, and that's 0:20:17.200 --> 0:20:19.439 what we'll explore when we come back from this break. 0:20:20.160 --> 0:20:23.960 Thank thank all right, we're back. So now it's time 0:20:23.960 --> 0:20:28.080 to talk about antagonistic pleotropy. In a paper in N 0:20:28.840 --> 0:20:32.600 seven and the journal Evolution, the American evolutionary biologist George C. 0:20:32.840 --> 0:20:37.320 Williams had a breakthrough that made metoirs original hypothesis even 0:20:37.400 --> 0:20:40.480 stronger and sort of complimented it. And so this was 0:20:40.520 --> 0:20:42.760 a paper that I mentioned in part one. Actually it's 0:20:42.760 --> 0:20:46.960 the paper called pleotropy, Natural Selection and the Evolution of sinescence. 0:20:47.720 --> 0:20:51.560 Williams hypothesis for the evolution of aging came to be known, 0:20:51.640 --> 0:20:55.320 as I said, as antagonistic pleotropy. And what this means 0:20:55.640 --> 0:20:59.240 is that, well, pleotropy, the word comes from the Greek 0:20:59.600 --> 0:21:05.480 roots meaning multiple turns or many effects. Pleotropy happens when 0:21:05.520 --> 0:21:11.040 a single gene codes for multiple different phenotypic effects, meaning 0:21:11.080 --> 0:21:13.960 effects on the body or effects on the behavior. So 0:21:14.000 --> 0:21:18.040 if you had one gene that both gave you black 0:21:18.080 --> 0:21:22.560 hair and gave you an extremely long, pinky fingernail, that 0:21:22.560 --> 0:21:25.040 would be pleotropy. Or if you had a gene that 0:21:25.200 --> 0:21:29.840 made you really tall and also made you better at 0:21:29.960 --> 0:21:33.640 learning multiple languages, that would be pleotropy. And there are 0:21:33.680 --> 0:21:36.439 lots of examples of this in animals in the real world. 0:21:36.760 --> 0:21:39.919 Here's one in chickens. Robert, have you ever seen the 0:21:39.920 --> 0:21:42.560 frizzle chickens? Who? I don't know. I've seen some pretty 0:21:42.560 --> 0:21:47.399 funny looking chickens before chicken. I mean the ones that 0:21:47.520 --> 0:21:51.200 have like the curly vegas outfits. Uh yeah, well yeah, 0:21:51.240 --> 0:21:54.000 I have seen some of these. These these chickens that 0:21:54.040 --> 0:21:56.200 have like a lot of extra feathers around their their 0:21:56.240 --> 0:21:59.560 talents and all. The frizzle gene is is a gene 0:21:59.600 --> 0:22:02.800 in chicken that causes the feathers to curl up instead 0:22:02.800 --> 0:22:07.840 of lying flat. So you get these crazy looking, like awesome, beautiful, regal, 0:22:07.960 --> 0:22:11.399 puffy chickens and they look really cool. But it turns 0:22:11.400 --> 0:22:14.840 out this gene also controls several other phenotypic effects. So 0:22:14.960 --> 0:22:17.720 if you are a chicken with the frizzle gene, you'll 0:22:17.760 --> 0:22:21.320 also have a different metabolic rate and different body temperature 0:22:21.640 --> 0:22:24.520 and lay a different number of eggs than the chickens 0:22:24.520 --> 0:22:26.919 who don't have this gene. So if you want the 0:22:27.000 --> 0:22:29.920 gene for the magnificent curl, you're going to be laying 0:22:30.040 --> 0:22:33.520 fewer eggs, among other things. And these are examples where 0:22:33.760 --> 0:22:37.159 the situation. It feels more like a trade off and 0:22:37.240 --> 0:22:41.120 probably has more in common with some of our our myths, right, 0:22:41.280 --> 0:22:44.040 because the gift of the god often comes with some 0:22:44.080 --> 0:22:48.120