Hello and welcome back to Introduction to Genetics in Evolution. The previous videos we talked about basic evolutionary principles and how evolution by natural selection is a mathematical inevitability. We also talked about how despite this there is some variation in how well people accept the truth of evolution and allow it to be taught in various schools. So in this lecture we'll talk in a little bit more detail about some of those basic principles of evolution, and we'll go into some of the evidence for evolution and common descent of species, common ancestry of species. So first, evolution has two fundamental processes. Okay? So you can have change within a lineage. So if you were to go far back in time, 60 million years ago, ancestors of the modern horse stood only about half a meter tall. Over the course of time, over the last 60 million years, you had the evolution of the modern horse, which today stands on the order of almost two meters tall. So we have this change within a lineage. These pictures, by the way, don't necessarily depict actual horse ancestors. But they show fossils that were present at the same time as the presumed horse ancestors. Okay? The other fundamental process within evolution is the formation of new lineages, or this idea of common ancestry of species. So if you were to go back many millions of years ago, horses, donkeys, and zebras all shared a single ancestor species. But then, they had this split of the single species into what became three new species. One of them involved into the modern horse. What evolved into the modern zebra? What evolved into the modern donkey? So, from taking these two processes, there are two fundamental principles of evolution that I'd like to emphasis. The first is that much of evolutionary change, much of what's happening within a single lineage, is caused by natural selection. And it's this natural selection that produces the appearance of design that I talked about in a previous video as being something that sometimes causes confusion for people and misunderstanding. The other thing is that all species, not just a subset, all species share common ancestry that not only do horses and donkeys have a common ancestor, but horses, donkeys and pigs have a common ancestor. Horses, donkeys, pigs, and mice have a common ancestor. We share a common ancestor with them. Flies share a common ancestor with us. Coral shares a common ancestor with us. Sunflowers share a common ancestor with us, and even the amoeba shares a common ancestor with us. There is a presumed single origin of life that then produces all the diversity that we see on the planet today. We'll talk about that a little bit more extensively in a later video but let's go from this into some predictions that come from this idea that most evolutionary change comes from natural selection and from the presumed common ancestor of species. Some of these, we've already touched on in previous points. First, if life originated on Earth a single time in the distant past, then what we should see is when we go way back in the fossil record, the earliest detectable forms of life should be very primitive. Should be very, very simple. Only later should you see some modern forms. Now, it's possible that later you'll also see some simple forms. But the earliest forms should certainly be simple. There's a famous quote from the biologist J.B.S. Haldane, that what observation would refute the truth of evolution and common ancestry. And he argued that what would do, it would be finding fossil rabbits in the Cambrian era, so this is very, very long time ago, finding fossil rabbits. That would refute this idea of common ancestry. Well, that's never been found, so there has not been an observation to refute the truth of evolution or common ancestry. Well in fact, when you look at the fossil record the early life really is extraordinarily simple. That you see things which are either single celled or very, very small and with very simple structures very early in the fossil record. And as you go later in there you start to see the earliest simple shelled animals, and much later do you start seeing things like plants or vertebrates, and only very recently do you see humans. So in general, yes. The earliest life we see evidence for is extraordinarily simple. We don't see these ancient vertebrates that are arising long before simple gastropods or other shelled animals. So that's one prediction fulfilled. Here's another one. If evolution occurred within lineages, and those lineages sometimes split we should be able to find cases of species gradually changing the fossil record from one form into another form. And in fact, I've actually already shown you the answer to this, in a case of horse evolution. When we look at ancient horse forms, going back in time we see all these sorts of transitions here. We see this gradual change over time in the shape of the horse, from the ancient horse to the modern horse. We see this not just in over all form but also in various other skeletal structures. So looking at, for example, their legs, the earliest horses there didn't have hooves, but had these individual toes, and you see this change over time towards, the modern hoof. Same sorts of things in terms of their molars. So again, we see this change over time as predicted from common ancestry and evolution. Another prediction we have is that if all creatures share a common ancestor we should see transitional fossils. Things that connect modern groups together. Now one case which would be very interesting in this context is the case of birds. Birds are actually glorified reptiles. If you look at how birds are related to all the animals, birds are actually nested within reptiles. So there are some reptiles that are actually more closely related to birds than they are to other reptiles. So what we should see then is some sort of transition from this ancient reptile, which had some characteristics of modern reptiles, to the modern birds. So we should see things like the evolution of feathers, we should see things that predate the beak, et cetera. In fact, that's exactly what we see. We see feathered dinosaurs that existed long before today. All right, so this is an example of Sinornithosaurus millenni. And if you look at it, it clearly does have feathers in there, we can see this in the fossil. But notice, it does not have a true beak, but in fact it has a mouth with teeth, even though it has a shape kind of similar to a beak. So this confirms this, but importantly, this also appears at the right time of the fossil record. This is found in deeper strata within the ground than modern day birds. This is one artist's conception of what this animal may have looked like. It's very colorful idea for it. Now critics of evolutionary theory often point to this idea of quote unquote missing links. They say, oh there are all sorts of missing links in the fossil record. And one kind of ridiculous example, and I think they would confess this is a ridiculous example too. What they give is that if you look at the modern crocodile and the modern duck you you don't see the transitional fossil which you might expect to be a crocoduck. That's just silly. Nobody expects there to be a crocoduck. The reason here is there is some misunderstanding. We expect transitions between ancient forms and modern forms. We don't expect things that are connecting modern day forms to each other. That would be more like a hybrid rather than an evolutionary chain. So let's look at this in the context of the evolution of cetaceans. Cetaceans are these large marine mammals like dolphins, porpoises, whales, etc. These are mammals. They breathe air. They are thought to evolve from land dwelling mammals. So they would share an ancient common ancestor with the hippopotamus as you see in this picture. Now if you go back in time, back to say 1970s, so not very far back in time. There were not a lot of fossil connections between the cetaceans that we see. Those living water dwelling mammals and land dwelling mammals. We have one example here, the Dorudon. Well, again as we started going through the fossil record between 1970 and today, more and more transitional fossils were found. So, I'll click through a few of these quickly. You don't have to know their exact names, but just to illustrate the point of finding these missing links over time. 1979, we have this form found. 1993, another transitional form. 2000 another transitional form. 2001, another transitional form. 2007 another transitional form. Now importantly these actually really fill a lot of the gaps that we see in the evolution of modern cetaceans. Some of these forms, such as this one right here were found around 40 million years ago. A lot of these other forms date back to 50 million years ago. So we see eventually, these forms that have characteristics of land dwelling mammals. But also have some of the characteristics of these aquatic mammals. And they're found at ancient times of the fossil record. Around the time you would expect these evolutionary changes to have happened. So there are not actually so many missing links as people would have you believe. There are some still missing, but that doesn't mean they don't exist. That's a very important point. So, I talked so far about a few predictions of common ancestry and evolution over time, driven especially by natural selection. Let's change gears a little bit and let me talk about some retrodictions. So these are observations that support the idea of evolution and common descent, but they won't necessarily have been things that we predicted ahead of time. And when we see them they support this idea. But if we didn't see them it doesn't necessarily mean that they don't support it. So these are things that are consistent with the idea of evolution by natural selection and common ancestry of species. One great example coming from this idea of cetaceans, coming from land dwelling mammals is vestigial organ and specifically, the vestigial hind limb bones of a grey whale. Gray whales don't have legs sticking out of their back. Yet we see these hind limb bones there. This is very difficult to explain except in a context of common ancestry. That ancient, ancient forms related to the modern whale actually did have these hind limbs. And over time they lost the hind limbs, but a couple of the bones have actually persisted over time. So this is a vestigial organ. It serves no known function in the modern gray whale, but it is something indicative of its evolutionary history. Here, by the way, is a picture of Jerry Coyne pointing at the hind limbs at a museum at Harvard. By the way, I should point out a lot of the examples I'm giving here are taken from a presentation by Jerry Coyne and are discussed in his book, Why Evolution is True. Another example related to vestigial organs is vestigial genes. These are genes that we see in our genome or the genomes of other species, but they don't work. They actually have some sort of disruption so they don't actually produce the proteins or the structures that they do in other taxa when they're normally functioning. So, one example here is the genes for making yolk proteins in mammals. So mammals, as you know, don't produce an actual yolk. They produce this empty sac that appears in the embryo and doesn't have the [INAUDIBLE]. So this is not something that's useful at all. Yet the genes for making these yolk proteins are actually found in mammalian genomes. Why would this be? Again, it makes sense in the context of common ancestry. That some of our ancient, ancient ancestors actually did make these yolk proteins. When we stopped needing them, they stopped making the protein but the gene is still there. Some remnant for it. The genes for making vitamin C are also not found in primates. I'm sorry, the genes for making vitamin C are found in primates. But we don't make vitamin C. If we don't take vitamin C, we get the disease called scurvy. We have to get vitamin C from our diet. But most other mammals, except for guinea pigs, actually produce their own vitamin C. You know, we have the genes for making vitamin C but they're broken. So why would this be? Again it's indicative of this change over time. That we have ancestors that actually did make their own vitamin C and then there's an evolutionary change that made us stop doing it. The last one I'll mention is olfactory receptor proteins that we primates are definitely lacking a lot of olfactory proteins that a lot of mammals have. We can't smell nearly as well as a lot of other mammals. Yet, those proteins, the genes for making them, are still found in our genomes. They just don't work. Let me talk about another set of retrodictions. These are related to biogeography. Basically where animals are found, or where plants are found in the world. Well, what we see in terms of biogeography is that when you look at very isolated oceanic islands, they tend to have many native birds and insects. But they lack amphibians, mammals, or freshwater fish that are native to those islands. Now why would this be? If life just spontaneously arose in multiple places you'd think it would be just as likely to arise spontaneously in a continental area as in an oceanic area. But you don't see these particular forms in these very isolated areas. Well there's two explanations. One is that life spread across these continents and the only forms that are found on these isolated oceanic islands are the ones that were able to get there. Right, the ones that were able to fly over there. The alternative hypothesis is that mammals or amphibians can't live well in these oceanic islands. We can test, and we have in fact, tested, unintentionally, the latter hypothesis. Mammals and amphibians have been introduced to isolated oceanic islands and they do extremely well sometimes. Here are two examples from Hawaii, the cane toad which was also introduced to Australia, which is both a continent and a very large island. It has done extraordinarily well there. This is an amphibian. It went in there, it's destroyed tons of the native fauna that are present on these islands. So clearly it's okay. The Indian Mongoose shows an example of a mammal that was introduced to Hawaii and again killed off a lot of the native fauna and big pest species there. But they can live on these oceanic continents. So we hypothesize that the reason that they're not found on these islands is because they couldn't get there. Another retrodiction related to biogeography is that the most similar species to those that you see on oceanic islands. So, if you, let's say you have some birds on an oceanic island, you should expect their nearest relatives, the ones most similar to them, should be the ones on the nearest mainland. Again indicating this idea that the animals that got to islands and became native species there over a long period of time are ones that were able to fly over there from the nearest continent. And in fact you do see that, if you look at isolated oceanic islands and their nearby continents, you tend to see very very similar forms. In contrast, if you look at an isolated oceanic island and look on the other side of the earth, you don't see things that are that closely related. The last retrodiction I'll mention, and I'll only talk about this one briefly, is that of inefficient design. That if an organism were to actually be designed from scratch, it wouldn't be designed the way it actually is. However, when you think of it in the context of being cobbled together over time from evolution, it does make a lot more sense. Now, one example that's often raised in this context is that of the laryngeal nerve that comes off the vagus nerve. Now in fish, this branch off the vagus nerve, you know it has a pretty short little transit down to the gills. No problem at all. What's a little bit less efficient is when you look at humans, or other mammals. So here's the laryngeal nerve loop, comes down, loops under the aorta, and then comes all the way back up to the larynx. So that's not very efficient, that's a long way for this to transit when it could just go, boop! [LAUGH] Just connecting right across like that. It's even less efficient when you look at the giraffe. It starts way up here at the brain, goes all the way down again, looping around the aorta, comes all the way back up, and connects over there. That's extraordinarily inefficient if its primary goal is to actually drive the larynx. That really doesn't make sense. However, probably what happened is, this nerve happened to be going around the aorta in an ancient form. There it didn't really matter. It couldn't cut and reconnect around it over evolutionary time because every one of the descendants of this ancient animal needed to have a functional laryngeal nerve. So evolution was working with the materials available. It couldn't actually produce a more efficient design. You can think of it in the context of retrofitting a house without ever turning off the electricity or water. That there's so many things you'd have to do that would be very, very inefficient that if you just destroyed the house and built it again from scratch, would be far more efficient. Well this is the kind of thing we see in the context of species out there. In later videos, we'll be talking about responses to criticisms of evolutionary theory. I hope you'll join us. Thank you.
