[0:05]Hi everybody, it's your AP Biology teacher Mr. Poser. Today we're getting into topic 7.6 on the evidence of evolution. All right, so in our first topic, um, for this unit, we spoke about what evolution is and we talked about how it is a theory, but it's not a theory just because it's some, it's Charles Darwin's just a guess, "Oh, my theory is, it's just a theory."
[0:20]No, it's uh, it's a theory because it provides an explanation for the nature of living things, right?
[0:30]It provides an explanation for the diversity of life, the unity of life, it provides an explanation for adaptation, and it provides an explanation for lots of observable phenomena from lots of different fields of study.
[0:44]And that's something that we're going to be talking about a little bit today. Now, the evidence to suggest that species come from other species and that species change over time, which is what evolution is all about, is astronomical.
[0:54]There's so much evidence, right? It's almost completely accepted by uh, the scientific community.
[1:02]Um, there's tons of evidence, all right, and I, that's a little beyond my pay grade a little bit to uh, to cover every single form of evidence that there is, um, to suggest that species change over time and that species come from other species.
[1:14]So, um, I'm going to cover what's going to be uh, required to know on the AP Biology exam, the AP Biology course and exam description, the essential knowledge in topic 7.6.
[1:26]That's what I'm going to be covering here today. All right. There's a lot more to it, um, than just what I'm going to talk about here.
[1:34]All right. Um, so let's get into it. And all these pictures down here are uh, what we're going to be kind of getting into today, um, as far as the evidence of evolution that shows species change over time and that species come from other species, which is what's called a common ancestry.
[1:46]Um, and uh, here's the evidence for evolution shows that, well, yeah, species change over time and species come from other species. Um, and the idea of common ancestry here, let me just explain in case we don't uh, have a firm grasp on that yet.
[2:00]All right. So, uh, think about your ancestors, right?
[2:03]Your ancestors are people that you descend from. Um, and uh, your family, right?
[2:09]Who are you more closely related to? Your cousins or your siblings? All right. If you have cousins and you have siblings, um, well, you and your cousins share the same grandparents, while you and your siblings share the same parents, or parents.
[2:19]Um, and uh, so who are you more closely related to? It's going to be your siblings, right? Because you have a more recent common ancestor.
[2:27]All right. So, species that exist today, more the ones that are more closely related to each other, um, are going to have a more recent common ancestor. Uh, and more the ones that are more distantly related to each other are going to have a more distant common ancestor.
[2:41]All right. Um, so evolution works in the same way as uh, as a family tree.
[2:46]One species gave rise to several other species, which gave rise to other other species, right? But they all have that same common ancestor.
[2:51]You can trace back to common ancestors. Um, and that's what evolution shows us time and time again.
[2:58]How do we know? Um, well there's geographical data, geological data, physical data, biochemical data, and mathematical data as well.
[3:06]Um, there's all sorts of different forms of from many different fields of study that all point to the same conclusion that yes, species come from other species and they change over time.
[3:14]Common ancestry is a thing. Okay? Um, so uh, let's start talking with about fossils, all right?
[3:21]Fossils are the, you know, once living remains of organisms, um, from uh, from typically a very, very long time ago.
[3:29]All right. And uh, we can see some change over time very clearly, um, by studying the fossil record.
[3:34]It clearly shows change over time in species. How do we know how old certain fossils are?
[3:39]All right. So, uh, check it out. This is a cool diagram about the evolution of whales.
[3:44]All right. Whales are mammals. They are not fish. Um, they don't have gills, they have lungs, um, and they produce milk for their young, just like any other mammal would, but they spend their entire lives in the water.
[3:57]All right. Um, now, how did this come to be? Well, they evolved from animals that walked around on land.
[4:03]Um, there's other cool videos on YouTube, um, about this as well.
[4:06]I suggest checking those out. I believe there's one from stated clearly that I really like about the evolution of whales.
[4:12]But anyway, um, check it out. So, if we examine each of these fossils here, we can show a pretty clear trend here.
[4:20]Um, that it's going from this small like land mammal here to these large aquatic animals.
[4:27]Um, mammals, I should say. All right. And you can see gradual changes over time. All right. But, uh, hmm, okay, let's check it out. This thing, this pacacetus over here from 50 million years ago, kind of just looks like a dog, doesn't it?
[4:39]Right? So, how do we know that this isn't just somebody's dog and it's a 50-year-old, excuse me, 50 million-year-old fossil from pacacetus from an ancient proto whale or Ambulocetus, same thing. How do we know that's not just like somebody's weird-looking dog or something like that?
[4:56]All right. And how can we actually sequence them like this? Well, we have to know how old the fossils are.
[5:00]On there's two ways to tell how old the fossils are. One is called relative dating and that sounds really funny, but it's not about dating your relatives.
[5:10]It's about uh, figuring out how old something is relative to the position of uh, something else, right?
[5:16]Um, so fossils positioning in rock layers relative to other fossils and rock layers can be used to determine its age. Um, so like for example, uh, these trilobites down here, they're in a lower uh, rock layer that was formed much earlier than these. And I forget what they're called, these animals up here.
[5:37]All right. So, we can assume based on their positioning in the rock layer and the sedimentary rock layer, that these trilobites are going to be older than these animals over here.
[5:43]All right. Um, fossil formation is a little complicated, right?
[5:46]But it takes uh, basically a fossil is kind of a cast made of sedimentary rock, um, that uh, of an animal's bones, basically, or an animal structure, exoskeleton.
[6:00]Um, right. So, uh, it it it takes some particular processes, all right?
[6:05]There's not uh, um, fossils located everywhere in the entire world because um, certain geological processes need to occur in order to make fossils, right?
[6:11]And uh, sedimentary rock, all right, forms in layers.
[6:15]So these layers that are lower down are going to be more ancient, and these layers that are higher up are going to be or more to the surface are going to be uh, slightly younger, you know?
[6:21]Even though 495 million years is not very young, you know what I mean?
[6:25]Um, but we can assume, okay, based on their positioning, what's older and what's not, all right?
[6:28]And we can see gradual change that way. All right. If we want to find the specific age of a fossil, we can use what's called radiometric dating, um, and that's based on how much of a radioactive isotope has decayed.
[6:41]Okay. Um, and a well-known radioactive isotope is carbon-14. We don't have to get into all the specifics about how radioactive uh, decay works.
[6:50]Okay, but um, in all living things, okay, there are what are called radioactive isotopes, and those are basically atoms that have basically too many neutrons, right?
[6:59]Uh the nucleus of an atom has protons and neutrons, right? And it has too many neutrons and it becomes unstable.
[7:05]Um, and uh, you know, it can't stay unstable forever.
[7:09]What's going to eventually happen is that it's going to decay.
[7:12]Those uh, that that nucleus is going to kind of like break down a little bit. It's going to lose some of its neutrons.
[7:17]It's going to become something else. Um, so carbon-14 decays into nitrogen-14, um, at a constant rate.
[7:22]And the rate at which we measured the decay of a radioactive isotope is called its half-life.
[7:27]All right. So, let's just say in an organism, um, it has 10 grams uh, of carbon-14 in it when it dies, okay?
[7:36]Um, so 10 grams of carbon-14.
[7:39]Carbon-14 is a radioactive isotope. You have carbon-14 inside of you right now.
[7:44]Um, now, here's the thing. Carbon-14 doesn't stay as carbon-14, right?
[7:49]It decays. It's unstable. Um, and it and it takes 5,730 years, or in other words, a half-life, in order for half of that carbon-14 to decay, to break down into nitrogen-14.
[8:01]Okay. So, check it out. If an organism has 10 grams of carbon-14 when it dies, um, 5,730 years later, it's going to have half the amounts of carbon-14.
[8:12]Oh, okay. That's why it's called a half-life, because half of it decays.
[8:16]Okay. And then another half-life later, another let's just say another 5,730 years pass, um, it's going to have half of the carbon-14 that I had before, so it's going to break it down into 2.5 grams.
[8:26]Okay. So, that means two half-lives have passed.
[8:29]Now, we can use half-life to determine um, and the concentration of certain radioactive isotopes to determine how many half-lives have passed and therefore how old is a particular uh, fossil.
[8:41]All right. And that's how we can figure out how old it is.
[8:45]That's how we can figure out like, oh, this is actually a Pacacetus and it's not just somebody's dog.
[8:50]Um, you know what I mean? So, there you go. Radiometric dating is how we find out um, specifically how old something is.
[8:55]All right. Another uh, piece of evidence that points to common ancestry regarding fossils, is that you can find fossils of the same or similar organisms um, all across the world.
[9:04]All right. Um, and the geographic location of fossils also helps determine common ancestry and explains the distribution of similar species.
[9:11]Okay. So, for example, uh, you could find tropical plants fossils all over the place.
[9:15]You can find in South America, Africa, India, Antarctica and Australia, which are very distant places on Planet Earth, right?
[9:22]But they all used to be stuck together, um, in one of my favorite names of anything ever, Gondwanaland, which is uh, these southern continents when they're all mashed together, um, after Pangea broke up.
[9:34]Um, breakups are hard. But anyway, uh, we can see um, trends here and we can see that uh, the locations of these fossils suggest that they all had a common ancestor, um, and uh, let's see.
[9:47]So, if another example of the distribution of species, right, would be like, for example, an anteater, um, a Pangolin, and, um, what's another one?
[9:59]Okay, those are those, and there's another an an an ant eater type species, um, that have a very recent common ancestor, they're very similar, but they live on opposite ends of the globe to each other.
[10:08]How is that? Well, they had a common ancestor that lived uh, when all these continents were, you know, pushed together, all right?
[10:16]And as these continents separated, um, these species diverge into uh, or the common ancestral uh, species diverge into others.
[10:25]And uh, that can that can explain how similar species can be found in very different areas as well.
[10:29]All right. So, the locations of fossils also helps determine the uh, common ancestry of species before I go too far down the rabbit hole there.
[10:37]All right. Um, morphological or anatomical similarities, basically that means similarities in body structures provide evidence for evolution too.
[10:44]Um, this is a classic picture up here. This is demonstrating what are called homologous structures.
[10:49]These are body parts with a common origin but have different functions in different uh, species.
[10:53]Okay. So, or descendant species, I should say. Okay. So, check it out. Why is this significant over here?
[11:00]Um, we are looking at the forelimbs of a human, a dog, a bird, and a whale.
[11:04]Okay. Um, and if you think about what a whale, or a bird, or a dog versus a human uses their forelimbs for, it's very, very different, right?
[11:11]Humans use our we use our arms and our hands to grab stuff, manipulate our environment and build things, and be really cool with them.
[11:18]Um, but a whale uses it to swim, a bird uses it to fly, a dog uses it to like run and like scratch your furniture and that kind of stuff.
[11:25]Um, so how is it that that, you know, what what what's the big deal?
[11:32]They use their forelimbs in different ways, but their uh, their forelimbs all have the same bones in them, the same patterns of bones, different shapes and different sizes, but the same bones in them.
[11:41]All right. In your arm, this arm, this bone right here is called your humerus.
[11:44]Okay. This one that uh, helps you twist your hand around, this is called your radius.
[11:47]This one is called your ulna. Okay.
[11:50]The white one is the radius, the red one is your ulna, this brown one is the humerus.
[11:54]Okay. Your wrist bones are called your metacarpals, or excuse me, your carpals, um, and then uh, the bones in your palm are called your metacarpals, the bones in your fingers are called your phalanges.
[12:02]Um, and you can see these same exact bones, different shapes and sizes and different modifications of it.
[12:08]Um, that's what evolution is, descent with modification. You can see different modifications of them in all these other different species that use their forelimbs for different purposes, but they have the same bones, which suggest they all have the same common ancestors, species that had those same bones in their uh, forelimbs.
[12:25]Okay. So, homologous structures are pretty cool. And you can find this in a lot of other um, examples across the animal kingdom as well.
[12:32]Okay. But homologous structures um, are something that's going to be coming up here.
[12:36]All right. The other form of morphological evidence that AP Bio wants you to know about are what are called vestigial structures, and those that have um, those are structures that have a greatly reduced function in living organisms, but they are inherited from a distant common ancestor.
[12:50]All right. Um, coming back to the whales here once again, because they're super interesting.
[12:54]Um, okay, whales are aquatic mammals, right? They have lungs, they have, you know, fully formed skeletons, they produce milk for their young, they're warm-blooded, um, they're very much mammals, right?
[13:05]But they live in the ocean their entire lives, right?
[13:08]Um, if you look at a whale skeleton, you can find these tiny kind of shriveled-up bones right back here, uh, towards the hind end of their body.
[13:17]And what are those? Well, those are very, very small hip and leg bones.
[13:21]Hmm, hmm, hmm, hmm, hmm. Why would a whale have very small hip and leg bones if it doesn't have legs and it's never going to use any legs?
[13:31]Well, that's because it inherited those hip and leg bones from an ancient common ancestral species that used them that used them for walking around on land.
[13:41]Um, snakes, all right, they also don't have legs, but they have leg bones, very, very tiny leg bones, um, that suggests that, hey, they evolved from a species that once had used for them.
[13:52]All right. Human bodies, we are riddled with vestigial structures, for example, our uh, tail bones.
[13:56]All right. They're very, very reduced in size. It's not it's not completely functional and anchor some of the muscles in your butt. Um, and say like your appendix, we're finding more that that it has uh, some uses for it, but it definitely is reduced. Um, because of uh, well, because of evolution, right?
[14:12]It's it's very, very much reduced and does not serve the same function as it did.
[14:17]Um, how why do we have it? Inherited it from a common ancestral species.
[14:21]Um, there's a whole lot of others, like the fleshy corner of your eye, your wisdom teeth, etcetera.
[14:26]Um, those are all vestigial structures. Why do we have them? Because we inherited them from a distant common ancestral species that once had a use for them.
[14:33]All right. Um, so vestigial structures are pretty cool. All right. And uh, once again, I want to show you this whale picture just to highlight here the legs, look, the legs, you can see them getting smaller and smaller and smaller over uh, the tens of millions of years of uh, cetation evolution.
[14:48]Citations are things here. All right, we can spend days talking about this, but I'm going to try and wrap it up here.
[14:52]Hey, um, last all this stuff about biogeography and fossils and um, comparative anatomy, all the morphological similarities.
[15:01]All right, that's all great. Okay. Um, but probably the most serious form of uh, evidence for evolution is just the similarities in genes, uh, genetic similarities, right?
[15:10]Um, who do you share more genes with? Your cousin or your sibling? It's going to be your sibling once again, right?
[15:18]Um, so we so species that uh, share more genomic similarities and amino acid similarities in their proteins, um, they're probably going to be more closely related to each other.
[15:28]They're going to have more recent common ancestor. All right. And we find this all over the place, um, throughout uh, throughout life, pretty much.
[15:35]All right. If we compare human uh, cytochrome C sequences to pigs and chickens and fruit flies, um, we can see a whole lot of different similarities.
[15:42]You can see it all over the place, um, in terms of uh, how many nucleotides are similar, how similar their genes are, how and of course how similar the amino acids are that make up the proteins.
[15:53]Um, so as I put up here, comparisons of nucleotides in genes and amino acids in proteins, um, they produce in different species show striking similarities and homologous genes, providing further evidence of common ancestry.
[16:05]All right. Um, so check it out. This is uh, the alignments of amino acid sequences in cytochrome C.
[16:11]Cytochrome C, big bonus points if you remember what it is, it's a protein involved in the electron transport chain.
[16:17]All right. Um, all these animals down here, and well, many, many others, all use oxidative phosphorylation to make their ATP, right?
[16:23]Just like we do, um, they all have a cytochrome C, all right?
[16:27]But the cytochrome C is slightly different between these different species.
[16:31]Um, and whoops, excuse me, the uh, more similar the cytochrome C amino acid sequences are, the more uh, you know, recent the common ancestor we have.
[16:40]All right. And then backs up a whole lot of other things, right? A human and a pig are both mammals, right? We're both have fur, skin, um, with hair in it, uh, mammary glands, that kind of stuff, we're warm-blooded, four-chambered hearts, um, all that stuff.
[16:55]Okay, is you would make sense that there's going to be a whole lot more similar amino acids in the cytochrome C of a human, um, versus a pig, all right?
[17:01]And there's going to be more in fact similarities between that of the human and the chicken, and especially the human and the fruit fly.
[17:09]Okay. So, uh, the human and the pig have a more recent common ancestor because of these similarities, and a human and a chicken have a more distant one, and a human and a fruit fly have a very distant one.
[17:20]Um, because of these uh, these differences in nucleotides, all right?
[17:23]But uh, there you go. Once again, it's showing us here that all these organisms have genes and have amino acids, um, that make up their proteins, but uh, the more similar they are, the more recent common ancestor.
[17:35]And I'm going to stop right there before I go too far down the down the rabbit hole here and stop rambling.
[17:41]All right, so here's our recap. Uh, evidence for evolution comes from geography, geology, physics, biochemistry, and mathematics.
[17:46]Molecular, anatomical, morphological, and genetic similarities all indicate common ancestry.
[17:50]Fossils provide evidence of change over time and common ancestry based on their age, position, and location. There's a whole lot of stuff that backs up the claim that species change over time and species come from other species.
[17:56]All right, we talked about fossils, how they provide evidence of change over time, um, the fossil record, just putting it all together, shows us, oh yeah, these species do change over time.
[18:04]Um, and they suggest common ancestry based on their age, which you can find from relative dating and radiometric dating, uh, their position, and their location.
[18:12]All right. Um, the locations of fossils and the distribution of species once again suggest common ancestry.
[18:18]Anatomical similarities like in homologous and vestigial structures can suggest common ancestry as well.
[18:23]All right. Why do all those animals have the same bones in their forearm?
[18:26]Why are uh, you know, why do whales have hip and leg bones?
[18:30]Once again, ancient common ancestors. Um, and then finally comparing nucleotides and amino acids in DNA and proteins of species also indicates um, ancestry and evolution.
[18:39]All right. It backs up all the other stuff, right? Charles Darwin didn't have access to, um, you know, genomic information or protein sequences or anything or excuse me, amino acid sequences or anything like that.
[18:50]But uh, what we're finding out using DNA sequencing technology, um, and some of the other biotech stuff that we talked about in 6.8, all points to the finger to like, hey, yeah, we common ancestors.
[18:59]We're all related. All right.
[19:02]That is it for this video. Please let me know if you have any questions.
[19:05]We will see you next time.
