Descent with Modification

hi. In this video, we are going to talk about evolution. Yes, we have finally made it to the moment where we're going to scratch beneath the surface and get at what is evolution. So evolution, in the simplest sense, is just the change in of phenotype in a biological population over time, or just change over time in the simplest form. Now, evolution actually is a very old idea, and it kind of predates Charlie Darwin. So the first guy who's really credited with coming up with the theory of evolution was called Lamarque, and his ideas were referred to as Lamarque is, um, and this is that an organism passes on traits to its offspring that it acquired during its own lifetime. And he believed that whether an organism used or didn't use a particular body part, that would cause that body part to be strengthened or weakened, and this would affect some change in the organism's phenotype. So his example that he used was that of a giraffe, and he said that, you know, drafts there, you know, they started out. They didn't have these really long necks, so they kept stretching their neck. Thio, eat those leaves, and so over time they grew toe have longer and longer next, because they were strengthening that body part. They're stretching those necks out. During the course of one drops life, it would stretch its neck a little bit, causing it to grow a little longer, little stronger. And it would pass that on to its offspring, who would then stretch its neck a little bit during its life and so on and so forth until you get longneck drafts. We know today. Now, of course, that is not how evolution works. For one thing, use and disuse doesn't strengthen or weaken body parts like that. It doesn't work that way. Evolution is much better thought of as the way Darwin put it, this descent with modification. So Darwin's ideas about evolution are such that individuals in a population have different traits, right? They have different Khalil's for different things, so they have different traits and some of these traits. Some of these trait differences rather can be inherited, and every generation Onley, some individuals air going to survive until they can reproduce, and some will reproduce more than others and additionally, some individuals survive better and produce more offspring because of certain heritable traits or traits that can be inherited. So basically, if we look at this giraffe example, what Darwin would say is all right, so early on you have some drafts with shorter next, Like we see here, you got drafts with longer necks and, well, those drafts with shorter necks. But they're going to die. They're going to die out because they are not going to survive as long or produces much offspring as the drafts with the longer necks. So those drafts with longer necks are going to be more successful in over time. They're going to become the most prevalent member of their population, and these short neck drafts they're gonna keep dying off. And Darwin called this process this process by which heritable traits become mawr or less common in a population because of differences in reproductive success between the individuals who have those traits. He called this idea natural selection. So essentially the drafts with long next we're naturally selected and became mawr common in the population. That trait of longneck became more common because it allow the drafts to get more food, which would allow them to survive better, which would allow them to produce more offspring. So this day differs very much so from remarks idea, right? These changes are not as direct. They're not as immediate. The whole process is a lot more passive in a sense. Now let's turn the page and talk about some more specifics about evolution.

So where did Darwin's ideas come from? I mean, he didn't just think them up. One day he actually came up with these ideas based on his experiences and one of the most influential experiences that Darwin had was his travel on the boat. The Beagle? Yes, like the dog like Snoopy. And he traveled on this boat or I should say voyaged because it really was a much grander expedition. He voyaged on the beagle to the Galapagos Islands amongst other places, and there he noticed some variation between the finches on the different islands. And this got him thinking he said, Huh, difference between these finches. Oh, get the gears turning Boom evolution. No, it wasn't that simple, actually, Darwin came up with some various ideas that helped him piece together the puzzle we talked about in the previous page. One of these ideas was something he called fitness, which is the ability of an organism to survive and reproduce. So different features are going to affect an organism's fitness. Now, another idea came up with is an adaptation. This is a trait that is maintained and evolved by natural selection that enhances the fitness of an organism So in looking at all these different finches, he noticed that the morphology of these finches, the way they appeared, was pretty different. And he assumed that due to different pressures on the different islands, different adaptations were favored in some places and not in others. And it caused these finches to become so different from each other, even though they were all kind of in this small area of these chain of islands. Now, a nice example of evolution at work is with the peppered moth, and it relates to this idea called industrial melon is, um so basically, industrial melon is amiss simply when organisms evolved darker pigmentation due to industrial pollution. So, you know, rewind time a little bit. Thio industrial England And before the Industrial Revolution, all the peppered moths or most the peppered moths anyways looked like this like they had pepper on them. Hence the name. But after the industrial revolution, pretty much all the moths looked like this one basically solid black. What caused the change? Well, the idea here is that because the environment changed right because of the industrial revolution because of the pollution that was getting into the environment, it made everything darker. So as the environment got darker, these light peppered moths became easier to see. Or as the the few peppered moths who were all dark colored. They had they were more fit. Their fitness was better because they were harder to spot on the now darkening environment. So over generations, what happened was these light colored pepper moths they got picked off. They were the ones who got eaten because they were easier to see. So they contributed less and less to the gene pool. The dark moths. They had more fitness, so they contributed more and more to the gene pool. So over successive generations there were fewer and fewer light colored peppered moths and more and more dark colored peppered moths. Now, you don't need to worry about knowing about the peppered moths in particular or industrial melon is, Um, I just think this is a really nice example off evolution at playing that was recorded by humans during human history. So another process in evolution that we can observe quite readily is artificial selection, and this is the process by which humans breed organisms for certain traits. And this was something that Darwin was quite familiar with and influenced his thinking about evolution. So a great example. Our dogs, various breeds of dogs have been selected by humans. The various traits of those breeds were selected for when humans. We're breeding these animals. And today we have a huge range of traits that different breeds of dogs can have. And just to illustrate that wide range of traits we have here a great Dane, a very, very large dog. And you might notice his coat is a lighter color. And then right here, we've got this anybody little black Chihuahua. So ah, lot of variation in color, size, shape, artifice. Official selection can produce ah, lot of different forms, just like evolution can produce all the forms that we see today. Now, one other example before we turn the page is corn. Yeah, corn actually used to look like this garbage, but you don't want to eat that. And you spend all this hard working time trying to grow this plant. You just get this little dinky stock of edible material that's not gonna fly. So humans selectively bred corn until boom. It looks like this like we know it today. So artificial selection has been a big part of human history because, well, humans have selected for various traits and farm animals, farm crops, all sorts of agricultural things. All right, now let's turn the page, Talk about some more detail.

so we can see these evolutionary processes happening during the course of human history. But human history is just a tiny speck in the range of geologic time. So how do we know about all the evolutionary changes that occurred before us? Well, the fossil record is a great place to start in. The fossil record is simply all the fossils found on Earth. And, of course, fossils are formed when organic tissues are mineralized or become inorganic and makes them stick around a lot longer. And this provides ah lot of evolution Evidence for evolution. Uh, we already talked about radio metric dating at the very beginning, which is how the age of fossils is determined. If you don't remember how that works, go back and watch the very first video, which covers that idea now. Fossils not on Lee can reveal the relationships between species. They also can show us extinct species or species that are no longer live like this. T. Rex right here. Now some species that have fossil remains air actually extent or still living, So just because there are fossils of a particular organism doesn't mean it's not around anymore. In fact, the very oldest fossils that humans have uncovered called stromatolites. These air basically fossils of, ah, particular type of bacteria. Well, those bacteria still alive and well today you confined living stromatolites on earth today, and you can find fossils of them that date back over a billion years. So this is a really long time scale. How do we think about things that far back in the past? Well, we use something called the geologic time scale. This is a measurement of time that relies on geologic data. Issue might notice this girl standing in front of this rock formation. This rock formation has all these layers in it. We call those strata, and geologists use these various strata to develop or they have used it to develop a geologic time scale. Now let's talk about what those fossils can be useful for. For one thing, we can compare fossils from extinct species to those of living species or other extinct species and see the relationship in the structures now. Occasionally you will have something called convergent evolution, and this is the independent evolution of similar features. For example, the eye has evolved separately over 16 times in the course of life on Earth. That's a lot. Another example would be the analogous wing structure that we see right here. So analogous structures have similar functions but independent origins. This phenomenon is also called Homo Place, and we'll talk about that when we talk about file A genetics. So right here you see these different wing structures on the top. We have a pterosaur that's a type of kind of like a type of dinosaur, and below it right here. That's a bat right. That's a type of mammal, and below that is a bird. And remember, birds are close ancestors to dinosaurs, so the wing has developed multiple times, and the wings between these different organisms is an example of an analogous structure and convergent evolution, the independent evolution of similar features. Now you can also have divergent evolution, where differences accumulate between groups leading to the formation of new species, and these will likely result in homologous structures which have shared ancestry or home ology but now look different and serve different purposes. And we have some great examples of this right here. You can see all the bones have been color coded between the human arm and hand the dogleg bird wing and this whale flipper. Well, guess what? These are all homologous structures. They have shared ancestry, but they've developed differently. There has been divergent evolution, which has caused them to look very differently today. But you can see that there is Hamal Aji between these structures because basically, it's just the size and shape of the bones that's changed. But all the same bones are more or less there. Now let's flip the page and talk about some mawr evolutionary phenomenon.

now just because birds evolved from dinosaurs doesn't mean that one day a dinosaur just gave birth to a bird. No, there were many transitional states along the way. And we call these transitional features. That's a trait that has a form somewhere between the ancestral one and that of the descendants. A great example of a transitional feature. Transitional organism, Actually. Is this the R key optics? This is kind of the missing link or one of those missing links between birds and dinosaurs. And you can see that the R key optics was a type of dinosaur, but had this feather had these feathers and it was starting to gain that bird form. So this is just an example of a transitional feature, the dinosaur turning into the bird. Some organisms have what are called vestigial traits, though, and these air structures their attributes that have lost their ancestral functionality but still stick around. Great example of this are whales back legs. Yeah, I bet you didn't know whales actually have the bones for back legs Now. Whales actually evolved from four legged mammals, so they lost the need for those back legs because their tails took over as their main mode of transit. What? But the bones for those back legs are still formed in Wales, and that is because they are a vestigial trait. They're kind of an evolutionary hangover from where they came from from their ancestors. Now some traits it's worth noting are non adaptive, meaning that these traits don't appear to be adaptive. And instead they have some sort of neutral or occasionally Della teary ISS effect on fitness. So basically, some evolved traits are not good for the organism, necessarily. And this really gets at some of the main evolutionary misconceptions. First and foremost, it's very often that we throw around the word complexity. This organism is mawr complex than that organism. Humans are higher order organisms than lowly bacteria. Guess what? Those aren't scientific terms, and in fact, those air really not scientific ideas. There's no definition for complexity. I mean, what really makes you more complex than a bacteria? Scientifically, it's very hard to define that term. Complexity is a very vague term that gets thrown around. Additionally, this sort of higher order, lower order hierarchy is also just kind of made up. There's no riel scientific basis for any of those ideas. I mean, really, what makes you so much higher order than a bacteria? Those bacteria have been around for a heck of a lot longer than you have. And, you know, assuming something terrible were to happen to the Earth and humans were to die out well, it probably be some bacteria that are still sticking around those air hardy, very resistant little guys. So in addition to that, it's important to know that evolution is constrained by genetic variation and what's already evolved. I you know, if there is not a lot of genetic variation in your population, then there won't be a lot of wiggle room for some traits to become more desirable than others. If if all the organisms or just all alike. Additionally, evolution is constrained by what's already evolved Now. What do I mean by that? I mean that every step that occurs in evolution is based on the previous step. So humans, for example, we could continue evolving in our form, could continue to train, but it would have to be based on the form we have now, right? We came from primates. Look at us. We still have a lot of the same kind of features that primates do because we can Onley modify what already exists. You can't create some completely new thing in evolution. It's always a modification of something that already existed. And lastly, evolution is not progressive. I mean, evolution will not continue to go along until it makes the perfect organism. There will never be the perfect organism, and that's because of fitness trade offs. These air basically compromises between traits. So imagine chicken, for example, and it evolves to produce more eggs. Yeah, that's a good evolutionary advantage, right? But guess what? There's a fitness trade off because now that it's producing mawr eggs, it means that it has to make the shells of those eggs a little thinner. So even though it's making mawr eggs, those eggs are more fragile. That's a fitness trade off, and that's the way things work in evolution. You make a little improvement on this thing, and often it's at the detriment of this other thing. So you can't create the perfect organism between from evolution and no such thing as complexity or higher order. And, of course, evolution is always just based on what came before it. So that's the reality of evolution. That's all I have for this video. I'll see you guys next time