 All right. Well, good morning. Second lecture on evolution. I'm going to always try to start off with just asking if there are any questions. So does anybody have questions about the last lecture? There wasn't. I mean, we basically went over what the form of a scientific theory of evolution would be. Especially, you have to make this uniformitarian assumption. And I spoke a little bit about Darwin with the main points here being that the fellow was wealthy and self-sufficient, like all these scientists were at the time. There was no real professional scientist at that time. He had a remarkable opportunity right after college to sort of see the world. But back then, the world really was unknown and like now. And so he was in a five-year voyage on the Darwin where he really formulated some of his ideas, at least. It was a good exercise in mulling over what he called the transmutation of species. Spent the next 20 years after the voyage amassing facts in support of his theory and really wasn't prodded into publishing until he had to, basically, until he was going to be scooped. Now, there are a couple of things I didn't mention. And somebody asked, why do I need to know about this? Of course, I said it and I put in the slides. I want you to have some general idea of what Darwin's life was like. But as in everything in life, you have to focus in on what you think are the more important things. And I try on the exams not to trick you up with trivial questions. The questions I put on the exam are things that I really think you should know. And I think Darwin's life is, yes, it is. So other people don't think so. How about now? OK, so if it's, yeah, I don't know what the problem is. But if you can hear me, that's good. If you can't, then you could move up as well, because there's still seating up here as well. So anyways, where was I? Oh, yes. And so he did spend the next 20 years in mass effects, but that wasn't the only thing he did. Of course, he got married, raised a family, lots of kids. But he also published a very popular travel log of his journey. It was for the general public. He published one of his first publications, Scientific Publications, was on the formation of coral reefs. And his explanation for our coral reefs in the South Pacific form is still the accepted model. And he also spent, believe it or not, an inordinately long amount of time studying barnacles of all things. So he published several monographs on barnacles. And the reason he did that was to sort of, I don't know what you say, get a street creds or something. Basically, he wanted to have the credentials so other scientists would take him seriously. And of course, they did. So by the time the Origin of Species was published, it wasn't like Darwin was some unknown figure. Other scientists, other naturalist biologists at the time knew about Darwin. Some even knew that he was working on this particular project and knew the outline of his theory. Now, just as an aside, there's been a lot written about him. Last year, February 12, 1809 was his birthday. So last year was his 200th birthday, so to speak. Obviously, he's not with us anymore. But a lot has been written on the guy. Lots of biographies have been written on him. And so if you're interested, I can point you to some biographies if you really want to read more about his life. But as far as we're concerned, the main publication that you, I should also say after the Origin of Species, he continued to write. He wrote a very influential book on the descent of man. So actually in the Origin of Species, he doesn't really even touch human evolution, but later he does. And he wrote a book on the action of earthworms, of all things. It turns out earthworms actually change the landscape a lot more than you can imagine. So you put a boulder out in the field, and over time the boulder sort of sinks into the earth. It's because of earthworms. And so Darwin was always enamored by these processes that act slowly, but surely over time it can have large effects over time. And so earthworms is kind of in its purview in that sense. But the Origin of Species is the main book we need to be worried about. It's a good book, it's an accessible book. So it's one of the most famous publications, scientific publications of all time. And unlike many of them, so I'll tell you that I, if I were to look at some of the physics literature, some of the foundations of physics, I would be lost, right? It's rough going. Origin of Species is a very famous influential scientific publication that is accessible now. So it's in principle a book that you could read and understand its arguments as well as anybody. So it's not a bad book to read. Now what I'm gonna do here is just outline the arguments he makes in the book. I'm not gonna go chapter by chapter, but I think there's actually kind of that order there. But I'm just gonna outline the major arguments he made. So let's start. Screen up, blank screen. And I think I can control the lights on the screen as full lights will do. All right, well that'll have to do. So he starts off the book talking about things that everybody at the time knew about. So you have to remember the Victorian era, which is when this was written, many more people than today have some experience on a farm. Maybe they're even raised on a farm, right? Now it's very uncommon. The last person in my family, for instance, who spent any time on a farm with my grandfather on just one side, is probably the same in your families as well. So people back then were much more familiar with the type of variation you would see in domestication. So he spoke about variation in domestic animals and plants, things that people understood, okay? And the basic argument he's made is something that nobody at the time would disagree with, nobody at today would disagree with either. And it's the simple observation that, you know, yes, I'm getting a message from back there. All right, so I'm getting a message from above that says that I'm not to use this board, but this one because I guess there's people in the neighboring lecture halls. Even though they realize that there's lots of space here, do we have to project to the other rooms now? So sorry for the interruption. We'll fix this, I hope. So I will walk right over here, I suppose. So let's do that. So you can talk about variation in domesticated species. Nobody disagreed with this, you can see it. So the basic argument is that it's like a litter of puppies, there's obvious variation. If you have horses, they vary one from another, okay? That this is not, this isn't rocket science as part of this argument, okay? The other, so the one part is that variation is there. Like I said, he's building up this argument starting with facts that nobody disagrees with. The next thing he talked about was that there's heritability. So offspring resemble their parents. Once again, this is an argument that nobody at that time would disagree with. In fact, farmers would use this fact that there's variation among individuals and that offspring resemble their parents to selectively breed organisms, right? So he also talks about selective breeding. So these are the main things he talks about early on in this book about domesticated organisms. Variation, there's resemblance between offspring and the parents, and that if you're a farmer or if you're interested, you can actually select for traits that you're interested in based on this variation. If you're interested in having a very fast horse, you breed together fast horses, right? You take the very fastest in your herd and you mate those guys. And those in the offspring will tend to be faster than the average horse. That's the argument. If you want a cow that produces lots of milk, you take your best milker and you always make certain you breed her. And if you have some cow that doesn't produce very much milk, you make certain you don't breed her. Okay, these are things that farmers have used for millennia, actually, before the origin of species. Whether or not they realized how they were doing it, but they did it. That's how we have domesticated crops, right? By breeding certain or making certain, only certain individuals reproduce, the ones that have the traits that we're interested in. Not necessarily the traits that'll be useful in nature, but the ones that we're interested in. Interestingly, Darwin, in the first chapter of the book, he amasses lots of facts on all three of these points. And he's spent a lot of time hobnobbing with pigeon breeders, for instance. So he actually started breeding his own pigeons. And so you have to remember, I believe that English society is still pretty stratified, but back in the Victorian era, it was very much more stratified by class than it is even today. And so to have a gentleman of Darwin's status, one of the few places you could actually see interactions between classes was in these sort of specialty clubs, if you will. So he would hobnob with people of different classes talking about pigeon breeding. And what he learned in his discussions with pigeon breeders is that if you wanted a certain trait, that pigeon in your birds, that pigeon breeder could give it to you, give it enough time. You want some specific feather ornamentation on the head, that pigeon breeder could do it. And you do it by looking for any individuals among the pigeons that are out there that had even the slight beginning of the type of variation that you're interested in. Then you can start to breed for more extreme variants of that. So if you want a big, tough to feathers on the head that you look for individuals that have at least some tough, tough, you know, the feathers then you can continue breeding for individuals that have more and more toughs on their head, for instance, okay. And one last point I want to make here is that he also argues that there appears to be no limit to the amount by which you can make these traits change. Okay, so as an example, here's, whoops, I have to go back to the, this is the first year I've ever had trouble with this in this class. So I don't know what's going on. There's another try. We're there. So anyways, the dog breeds for another thing that people are familiar with and that he discusses in the origin of species. And the ancestor of dogs was a wolf, right? So this is well known now. So there's been lots of studies. You know, wolves and dogs obviously interbreed. I used to have a dog that was half one quarter wolf. But you know, so that they obviously interbreed they're the same species, but humans are the ones that, you know, selected for different traits to generate the great variation that you're aware of in dog species. We have these little tiny things here, giant dogs. This, by the way, is the dog that I promised my daughter when we moved up here to Berkeley from San Diego. It worked like a charm, a golden retriever. But the point here is that this is the type of variation that you guys are familiar with as well. This was all produced by selective breeding for different traits. And in fact, this dog, I'll just give you a little bit, it's interesting because golden retrievers, you know what they're like. They're kind of tennis ball crazed animals. But this dog came from my PhD advisor who's in central Texas and he's a hunter and obviously a very good biologist. And so he and some other Texas hunters who happen to be professors at different Texas universities are trying to breed golden retrievers that are good hunting dogs but have less guard hair along the fur in the bottom. If you see golden retrievers that are very, you know, long guard hair, the fur that hangs off their stomach. And they're trying to breed dogs that are gonna be good hunting dogs in Texas where it's hot as hell during the summer and they have to run through tall brush and they don't want the dogs become fouled with all sorts of burrs and stuff. And so this, my dog actually is one of the results of this and she's a beautiful golden retriever, clearly a golden retriever, but she's not as toughy as a lot of these golden retrievers like the show golden so we don't talk about in our family, okay? So there's just an example of some, you know, the types of variation that we can see under domestication that's caused by just selecting for those traits that vary naturally within a species. So that is the first part of his argument. He then changes just a little bit and says, look, that's what happens in domesticated organisms. He then turns his attention to variation in the wild. And he makes at least two points here. He says that, look, if you go out and look at organisms that aren't domesticated, that we see the same sorts of things. We see that organisms vary one from the other, okay? And you have to remember this is a time where the hobby, so to speak, for a lot of Victorian people was to go collect things. So this was a time when people liked to collect, like, well, there were lots of burrs, they liked to collect things like eggs, beetles, insect collections. Often you go into a house and if it was a well-cultured family, they would have a curio cabinet where they would have displayed some of the things that they'd collected, rocks, organisms, whatever, okay? And so people were aware once again that organisms varied in nature, okay? That was not a surprise. And he argues that the type of variation you see in nature is of the same sort and the same degree as we'd see in domesticated species. And he also argues that the variation you see in the wild is also heritable, that is to say, once again, that offspring resemble their parents. Once again, nothing controversies. He realized he had a very explosive idea. He wanted to present this idea very, very carefully, right? He didn't want people to be turned off from the idea once. So he starts off in kind of the way a cagey salesman would. So you know how salesmen work. My kids were always really upset by this guy that sold this oxy-clean thing because he always would interrupt their cartoons or whatever it was that they were watching. But he would do things like, do you want to be well-liked? And of course you'd say, well, yeah, I want to be well-liked and do you want to be good looking? Well, of course I want to be good looking. You want to be successful? Yes, I want to be successful. And then he drops it on you. Then you need to buy my Herodgel product, right? Darwin is doing the same type of thing. He's telling you things that of course the only response is yes or I agree, right? I do believe in people who say yes, of course. Things vary. Of course offspring resemble their parents and of course people can breed for the traits they want. And yes, we are aware that in the wild we have variation and that the variation is the same type and the same degree that we see in living species. So these were things, these were arguments that nobody found controversial, not at all. And the third point he makes is a little bit more controversial. It's something that people could be convinced of but they hadn't thought about it. He talks about the struggle for existence. Now why this was a more controversial statement is because at the time people had this idea of what you might call natural theology. That is to say that out in nature things are great. That it's sort of a harmonious working of parts that there isn't a struggle for existence. That nature was made for the use of humans. So this is sort of this harmonious, that nature is sort of a harmonious working of parts. Darwin says no way. If you look out there in the real world and he was a very devoted naturalist, a very keen observer, he says, what you see is things eating each other, right? That's not harmonious at all. You see lions chasing down the gazelle and eating them. You see the gazelle running away from the lions as fast as they can for dear life. You see that if you look within a species you often see not organisms working together but stepping on one another to get access to mates, for instance. It's not harmonious at all. And the main thing he talks about is that excessive reproductive potential. I don't think I call it in the notes but you can call it whatever you want. But the basic idea here is that organisms have the potential to produce many, many more offspring than could ever live. I don't know if you've ever worked in a lab but you take one little E. coli and in the right conditions, 37 degrees Celsius, overnight you can have a culture than that flask that's so dense that they start to die. But you can imagine that if you had just gave it a big enough flask, if you could make the entire world a flask, that within maybe a month you could have a world-sized flask just chock full of E. coli. I'm just giving you a made-up example. But he used the example of elephants. Even elephants have a remarkable access growth potential. You've given them enough time and without elephants dying natural causes or being, they could actually populate the world, need to be knee-deep or I guess it wouldn't be knee-deep, you'd be many heads high in elephants before you know it. So they have an excess reproductive potential and here he was very influenced by an essay by Malthus which you've probably heard of this name. People sometimes still talk about Malthusian crises. Anybody know what that is? Too many people, right? So that's not a new idea. Malthus wrote his essay in the 1700s, right? And the basic idea is that if you were to sort of make a plot, you know, here's time and then here's, well, we'll say how populations grow. You typically see this type of pattern. This is typical of human growth as well. You see what's called an exponential growth pattern. It's, this is a, all organisms pretty much have the same type of population growth potential. But what do you say about the food supply? Well, the food supply doesn't act by one organism doubling and having two which gives you an exponential pattern. It means you add a new field, right? It grows linearly. And so he says, look, if you look at the, how crop production increases, it grows linearly. And the concern was at some point in the future, Malthus' concern, I guess it's still a concern that many people have now, is that at some point the population, human population will outstrip food production and then we're in trouble. Now of course, the reason why we've been able to put off a Malthusian crisis for so long is because of selective breeding, right? We actually, our crops are much more productive than they were in the past and we've industrialized crop production and so forth. So we've been able to increase the food supply much more quickly than just linearly but the concern still holds, right? But he says that the same sort of situation holds for any organism where they always have this very excessive population growth potential but the resources are always gonna be limited, okay? So there's gonna be by necessity, by necessity some sort of struggle for existence. Now this, like I said, was a little bit more controversial but it was still a point that people could believe. The first two points I made, variation in the wild and in domesticated organisms, no problem. People already knew that, he's just telling them what they knew. This is the first point where he starts to talk about something new or at least something that may have been unfamiliar to many of the readers at the time but it's something they could believe. They just had to be convinced that, oh yeah, okay, well in nature things aren't as harmonious as I thought or assumed, okay. All right, so in the fourth part of his argument he drops the big one. This is where he introduces the idea of natural selection. Do you wanna buy my hair gel, so to speak? He argues that if individuals have some sort of variation, some, they bear a trait that allows them to better reproduce or survive in this struggle for existence that they will leave more offspring in the next generation and because of the fact that offspring resemble their parents, the offspring will tend to have that trait as well and also reproduce and survive better. And by necessity, by necessity you have to have a change in the frequency of that trait in the next generation. If you're the individuals with a particular trait or the ones that are surviving at a higher rate and reproducing at a higher rate, then that trait has to be disproportionately represented in the next generation. That's all there is to it. Right now if he had stated this argument flatly in the very beginning of his book, like I imagine he was very tempted to do, it's hard to know how people would have responded to it, but he basically built up the argument leading to this point. And so it was much easier to believe the individual arguments, the individual components of his argument, variation, inheritability, and the struggle for existence. Those three things together necessarily lead to that trait, traits that allow you to reproduce or survive better. It necessarily leads to that trait being represented at a higher fraction or higher proportion in the next generation. That is the key argument. This argument is why Darwin is justly famous because it's a natural process that can lead to adaptation. It's a natural process that can lead organisms to become adapted to their environment, bear traits that look as if they could be designed but were actually the result of a natural process. Is that clear? This is something I would expect you to know as it's sort of the foundation of all evolutionary biology. Okay, so there's a couple of things to note here. One, I can call it A, is the species that changes. Unlike the Marx theory where the individuals might be changing over their lifetime and then leaving the traits that had changed to their offspring, this is one where organisms either have the trait or they don't, right? Organisms either survive to reproductive age or they die. Individuals either at reproductive age reproduce or they don't, right? The individuals, their genetic makeup is not changing over time. It's the species, the composition of the species that is changing. The composition of the frequency of different traits in the species is what's changing, not the individuals. The individual makeup of a species is, right now our species is composed of all the individuals in this room and all the individuals outside of this room, right? In the next generation, there'll be another set of individuals and that generation may or may not differ in its frequency for different traits, okay? But the point is it's not us that's changing. It's the differential reproduction and survival of us individuals that determines the composition of the next generation. That should be obvious. So that's one thing. Another point he makes is that traits can evolve under natural selection only if they are beneficial to the individual, okay? That is to say that there can only be beneficial to those individuals bearing the trait. So what he's arguing is you can't have traits that are evolving because they help somebody else out. So this is one of his key arguments. He says if you ever find that situation then his theory is in trouble, okay? Now, normally I would give a lecture on what's called kin selection, which is the evolution of altruistic behavior and this is something that people pondered for a long time, how could altruistic behavior, seemingly altruistic behavior ever evolve? And the answer is basically you're helping individuals that are closely related to you. So things like wasps and bees where you have this hive and some of the individuals forego reproduction, you're actually helping those individuals that are foregoing reproduction are actually helping out very highly related individuals. So we've actually got the theory that can explain seemingly altruistic behavior, but if we ever see a case which, for instance, altruistic behavior that can't be explained because you're helping out related individuals, then the theory is in trouble, okay? And he states that right up front, okay? So the first four parts of his, first four chapters of the book actually do introduce the argument just as I laid it out. He then sort of, the rest of the book, he basically talks about the ramifications of the theory. And the first thing he does is he tries to head off what he considers potential criticisms of his theory. So where was I, I'm on five, right? Okay, so he's gonna try to answer what he knows are gonna be some of the criticisms of his theory. One is the lack of intermediate forms. Okay, now he argues that there's two types of intermediate forms that we could be talking about here. Okay, and so I'm gonna talk about each one individually. So the first one he talks about is one that's easy to dispose of quite quickly. So if you have A and B, he argues why do you not see species, for instance, living today that are all intermediate between A and B? Why do we not see all the different potential gradations between species? Why are there gaps in what we see out there in life? Meaning gaps in the form or the how species look? Why do we not see a continued gradation between humans and chimps or any other two species that you might choose? And this one he disposes of quite quickly. He says, look, during the evolution of these organisms, they continue to evolve. It's not like you have to leave descendants species at every single intermediate point. This is not part of this theory. It's just that you have a population, or we'll talk about population, if you talk about species, the compositions change and it doesn't mean you have to have at every single generation or every single intermediate point those individuals surviving to the present. They continue to evolve into the next generation. So that argument was pretty easy to deal with. The one that's a little bit less easy to deal with is there's a prediction that's made here. The idea is if we were to go into the rock record, if we were to look back in time, we should see the intermediate forms between these species. That is to say, sure, things change from one population to the next or one species generation to the next, but that does predict that those species, there was some species, or the species was alive in the past, first of all, and the question is why do we not see representatives of that species at intermediate points in the fossil record? And that's it. That's all there is to it. So we should be seeing all these intermediate forms. And its argument is a simple one and one that's been well proven today is that the rock record is an imperfect one. The geological history of the earth does not, first of all, not all rocks are represented for all time that's out there. And secondly, the fossilization process, the process by which organisms make it into the fossil record, is a rare one. It doesn't happen on a, well, maybe happen on a daily basis, but it's not like you can expect every intermediate to be found. And so this is something that was beginning to be well understood at the time. This is basically the early 1800s, late 1700s was a period where a modern geology was being founded as a science. It was largely at least at first being done by people that were building canals. So these engineers were building canals around Great Britain to move freight from one place to another. Of course, when you dig a canal you're digging into the earth. And what they saw is that when they dug into the earth they were exposing rocks which occur in layers if they're sedimentary. They're formed by the formation of particles settling out of water. You can see these sedimentary rocks if you drive anywhere really and look at road cuts where people cut through parts of a hill to make the road more level, those are road cuts. You look at these road cuts you'll often see sedimentary rocks exposed. They form layers, these layers are called strata. And at that time people were starting to realize that the strata could be dated not by putting years on them. That's something that was only occurred in the 1950s when people were able to radiometrically date rocks. But they were able to discover the relative order of the rocks. And they were able to name groups of rocks from specific periods of time. So if you've heard of the Cambrian period or the Cretaceous, you guys will be required to remember the periods of the earth later when we get to it. But they were just starting to name the rock layers. And the one way they did it is they realized that different rock layers had their own composition of fossils. That if you looked at the oldest rock layers, you didn't see any fossils. But some of the younger ones would have things like, you might first see the lowest rocks having trilobites, things like trilobites. And some of the later ones having more mollusks, things like snails and clams. And the more recent, the layers that were near the top had organisms that most closely resembled the species that are alive today. That's one thing that they understood before Darwin wrote The Origin of Species. What he argued was that there's, and what I sort of mentioned in the first lecture is that when you look at the exposed section of rock like this, most of the time isn't in the rock. So if you were to say, okay, where is the time in this sequence of rocks? The time is actually in the layers between the rocks. As I say, most of the time is represented by no rock at all. And all that means is that rocks don't form continuously except in some sedimentary environments like the deep ocean is where you actually see the most constant formation of rocks. Most of the time rock formation is very episodic. And by necessity, because fossils are only found in sedimentary rocks, therefore the fossilization process is also sporadic. Now we will talk in more detail in a later lecture when I talk about fossils and the fossil record about the process of fossilization. It's a field that's actually called, it's got a name, I'll introduce it to you now since I'll talk about it later. Tefonamine, it's a sub-discipline in paleontology, if you will, that studies how fossils are formed. Basically it's the study of everything that occurs from the time an organism dies to the time it finds itself in a museum cabinet. But anyways, his explanation for why we see intermediate forms in the rock record is because the fossil record is imperfect. Now what is known, what was known at the time about the fossil record was consistent with the theory of evolution. For instance, this progression of forms with the most recent ones, the top layers, the youngest rocks bearing organisms that most closely resembled the organisms living today, that was known. What's been discovered since is probably beyond Darwin's wildest dreams, in terms of finding intermediate forms. And we will talk about some of the most spectacular intermediate forms when I get to the fossil record lecture. But for instance, we have a well-documented sequence between, say, birds over here and crocodiles. So crocodiles and birds are each other's closest living relatives. And we have lots of fossils, including things that we call dinosaurs down here that are intermediate between crocodiles and birds. Birds are actually descended from dinosaurs, as we'll find out. And we can actually, there are certain dinosaurs that very closely resemble ancestral birds, as we actually have a pretty good sequence of intermediate forms. We also have good intermediate today, at least, not at Darwin's time. We have a good intermediate form between whales. I think cow would be a good example here. Closely related mammals, right? Whales proved to be really difficult to place in them. They always, people always knew their mammals, of course, but they proved very difficult to place in the evolutionary tree of life because they are so different. Their environment is so extreme that they've had all sorts of adaptations and it's very difficult to recognize any features in common between whales and other critters. But in the last, actually last just couple of decades, all sorts of intermediate whales, including some that have well-formed hind legs and structures in the ankle that are the same structures as we see in things like cows. So anyway, so just to give an example of some intermediate forms we have today. But at the time Darwin wrote, there were some examples of intermediate forms, but the fossil record was poorly understood and he just sort of brushed it off by saying, look, the fossil record's imperfect, but what is known as seems to be consistent with my theory. All right, so that is one thing he talks about. And large transitions, okay? So what he means by this is how do we get really complicated structures? How do we get something as complicated as the eye, for instance? You look at the eye, there's lots of pieces that all interact together to produce something that I can focus, not as well as I used to be able to, but I can focus on you. There's mechanisms that keep my eyes watered, that keep material from getting into it. It's a remarkable device when you think about it, right? And the question is, how do these large transitions occur? And he argues that during the course of the evolution of any complex structure, all the intermediate forms have to be beneficial. They should be better than what came before, okay? So if you can come up with an example where the intermediate forms don't work well, that would be a problem for the theory, okay? So eyes are actually not a very difficult situation. I'll show you an example in the slides in a bit, but it's such a mental exercise to get the projector switch that I think I'll hold off a little bit on that. But basically going from organisms that you can actually see out there today that just have photoreceptive cells on the skin, to things that have those photoreceptors buried in a pocket so that they can actually tell a little bit more of the direction from which a light source is coming, to things that have sort of a pinhole camera arrangement in the opening here, but the photoreceptors down here at the bottom of this pocket, if you ever made a pinhole camera, you know you can kind of focus things a bit, or at least get a more sharp image with a pinhole camera, to things that have a lens with photoreceptor cells in the bottom. These are the types of transitions that people, I mean, turns out frankly, eyes aren't very difficult to evolve. They've evolved many times, dozens of times it appears in the course of the history of life. And these are just the types of eyes you can see among mollusks, with for instance, squid having quite complicated eyes, and other mollusks having, like some clams having just photoreceptors, okay? But basically, with eyes, it's not such a difficult argument, but what about wings, right? I'll argue that if I'm in an airplane, I don't wanna see my airplane have half the wing length that had before, right? Half a wing is not very useful. You either fly or you don't, okay? And so there's some structures where it's difficult to, or more difficult at least, to argue how could that complex structure have evolved? To fly you need to have just the aerodynamics necessitates having a wing of a certain length. If you have a wing half that length, you're not flying. And so one of the arguments he makes is that in many cases it could be the case that a structure that is now being used for one purpose actually evolved for another purpose. So for instance, going to the wing example, at least with the birds, a lot of the features we associate with flight, such as feathers, actually are found in dinosaurs that could not have flown. They didn't have wings, but they had feathers, for instance. So a lot of the structures, so whatever feathers are used for now and during flight, and they're actually well adapted for flight, they didn't evolve for flight. They evolve for some other purpose, perhaps thermoregulation, we don't know for sure, but they certainly didn't evolve for flight. Hollow bones is another hallmark of birds, which is an obvious adaptation for flight, right? You make a bone that's less dense and less heavy. But it turns out that hollow bones are found in things like Tyrannosaurus rex, things that obviously didn't fly. So what in the Tyrannosaurus rex is on that march towards birds, so to speak. So clearly, many of these dinosaurs had hollow bones and did not fly, and the hollow bones in birds are just inherited from these ancestors. They're now used because, I mean, it's very useful to have them for flight, but they did not evolve for that purpose. So there's some, go ahead. Diving, what, to hold more air, I think? I think they might actually, there's some sort of complicated pneumatic system in birds for oxygenating blood, and I believe that the bones play a role in that. But it might actually, I don't know for a fact about this, but people have studied the bones and dinosaurs with the thought being, you can actually tell warm-blooded versus cold-blooded creatures by how the bones grow. And so there's this controversy among paleontologists about whether some, at least some dinosaurs were warm-blooded, they were able to regulate their body temperature. But I don't know if these dinosaurs could actually use the hollow bones for the same purposes that birds do today. But for whatever reason that you have these hollow bones evolving, it wasn't for flight, is my main point here. Okay, so anyway, so he does talk about these concerns he had, and he actually writes in his diary that sometimes he stayed up late at night worrying about eyes. All right, so the sixth part of his argument was a little bit more positive. So the fifth part he's arguing, look, these are some of the problems that I know you're gonna see, but let's talk about them. The sixth part of his argument is, hey, but you know, I can actually explain a whole bunch of things that the current model of how species formed can't, okay? So, neat things he could explain. So I'll just reiterate, you know, he says, look, the fossil record's imperfect, but what we do know of the fossil record is consistent with this theory of natural selection, evolution by natural selection, okay? And I should point out at this point that a lot of people talk about intermediate forms, and some people like to point out, well, this fossil record is never complete enough for their, you know, you can give them a very complete sequence of intermediate forms, but then they start to point to the intermediate forms and say, well, what about the intermediate forms between these intermediate forms, right? So you can keep going down, you know, you can't, there's gonna be a limit to the resolution that fossil record has. But there's another aspect of the fossil record which people forget, and that is that we can make predictions about when we should find intermediate forms. So it's not like just the presence of the intermediate form is enough, but the theory can actually predict with other observations we have when intermediate forms should be there. So for instance, I'll give you one example that you're probably gonna be interested in. It turns out that humans and chimps are each other's closest relatives. The chimpanzee is more closely related to us than the chimps is related to, say, the gorilla. That's a remarkable fact that we're most closely related to chimps. And the molecular data, so we can actually, we have full genomes of humans, we have the full genome of chimps, we have the full genome of gorillas now as well. But even before we had the full genomes, we had bits of the genomes, individual genes. And the prediction based on the molecular data said that this split occurred somewhere between, say, five and seven million years ago. The common ancestor of human and chimps probably lived about five to seven million years ago. So what does that mean? It means if you're somebody like Tim White, who's in my department and you're a paleoanthropologist, you don't go to Cambrian rocks, rocks that are about 500 million years, and look for humans, right, or our ancestors. You could look and those rocks have been well worked over by other paleontologists, but nobody's ever found anything that remotely, not having found a mammal in Cambrian rocks, 500 million years. What Tim did is he, we had examples of humans that go back, well, certainly lots of representatives here. We had things like Lucy that you've heard of, Australopithecus afarensis, which we'll talk about, somebody we'll talk about in the last lecture, about, what is that, about three million years ago. But that was the oldest we'd really had. There were like a few scraps, like a few molars that are about five million years ago, but that's not super exciting. So he said, look, I'm interested in this part of human history, the part that's the oldest. And so he went to rocks that were about four million years old. He didn't go to rocks that were seven or eight million years ago. He went to rocks that were four million years ago. And then he went to the place that chimps live in Africa. So he went to Africa. He didn't go to Siberia and look for these things. He went to a specific place where he thought he would find them because they're living, they're closest living relatives of humans live there. And he found it. He found human ancestors or hominids, things that are on this line leading to humans, about 4.4 million years ago, that are 4.4 million years old. This is, once again, it's a very imperfect record, but our record of humans, for instance, have a sort of admirably complete set of transitional forms for lucky for us. If chimps ever become interested enough in their own history, they're out of luck. There's only one arm bone that's known in the entire lineage between chimps and the human chimp lineage on this side. And it's because chimps live in forests and forests don't preserve fossils very well. You die in a forest and you're just eaten up by and decay very quickly. It's very grim. But the ancestors of humans lived in an environment which was more conducive to fossilization. We're lucky in that respect at least. So anyway, so what was known about the fossil record was consistent with this theory. Oh, he talks about fossil record, biogeography. Biogeography is the study of the distribution of species on the planet, where they live. And he argues that, for instance, you're all aware that there's lots of marsupials in Australia, things that like kangaroos that hop around, quala bears, all these things that are marsupials. They have a pouch and they're young or born very prematurely, but then they do a lot of the development in a pouch. Those are marsupials. Why do they all live in Australia? Why do almost all of them live in Australia? Well, the argument is that their ancestors lived there. So he could explain why species that are similar in their traits live in one place or in one area. And that's because their ancestors lived there. That's easy to explain with the theory of evolution by natural selection. Not so easy under any other theory that was present at the time. I think I wanna take a quick break and go to a few of the slides. See how this will work. Switch. See if it goes smoothly this time. Okay, so here's just an example of some of the different types of eyes you find in mollusks going from photoreceptive cells that are just on the, that just say yes, something's there to the photoreceptive cells being in hollow disks. These are the different forms that can be found just in mollusks. And this is what I wanted to talk about with biogeography that this is just the study of the distribution of organisms and a good example is the species that are found in the New World versus the Old World, the New World being North and South America, the Old World being Africa, Europe and Asia. And what you see is there's a greater similarity within this area, within these continental areas than between. So as an example, might have heard of New World and Old World monkeys. The New World monkeys live in the New World, right? And they're found in South America, they have a flat nose, so they all have similar features and they have three premolars. Whereas the Old World monkeys, and we're more closely related to these guys, live in Europe, Africa and Asia, they're Old World, they have a hooked nose and they have two premolars. But this is a pattern that can easily be explained by evolution because you just pause it that the ancestors of these creatures also live in those same areas. And so the reason why we have all these New World species with three premolars is because their ancestors lived in the New World and they had three premolars. That's all there is to it. I'm going to start, this will be the first thing I say in the next lecture. And so I've got a little bit more I wanna finish up here and then we'll move on to the math, the mathy part of evolution, which I know you guys are gonna look forward to. So, see you next time.