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And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phe... | Variation in a Species (3).mp3 |
There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much th... | Variation in a Species (3).mp3 |
My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think a... | Variation in a Species (3).mp3 |
So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's g... | Variation in a Species (3).mp3 |
Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of... | Variation in a Species (3).mp3 |
What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let... | Variation in a Species (3).mp3 |
For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of ... | Variation in a Species (3).mp3 |
Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or m... | Variation in a Species (3).mp3 |
We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll g... | Variation in a Species (3).mp3 |
And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then... | Variation in a Species (3).mp3 |
Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is go... | Variation in a Species (3).mp3 |
There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every spec... | Variation in a Species (3).mp3 |
So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amo... | Variation in a Species (3).mp3 |
And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called cros... | Variation in a Species (3).mp3 |
And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that e... | Variation in a Species (3).mp3 |
It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. An... | Variation in a Species (3).mp3 |
And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code fo... | Variation in a Species (3).mp3 |
I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way... | Variation in a Species (3).mp3 |
Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the dif... | Variation in a Species (3).mp3 |
And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it becau... | Variation in a Species (3).mp3 |
And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main sou... | Variation in a Species (3).mp3 |
But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It ... | Variation in a Species (3).mp3 |
It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have... | Variation in a Species (3).mp3 |
But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for ... | Variation in a Species (3).mp3 |
And so the whole time that we go through this video, think about these two ideas. And then even after watching this video, look at ecosystems around yourself, even ones that you are part of, and think about how energy flows and how matter is recycled. So let's first think about energy. So the energy for most ecosystems... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
So the energy for most ecosystems originally comes from the sun. There are other sources of energy. You could think about even moonlight, but that essentially comes from the sun. But there's also geothermal energy, but the sun is the source of most energy for most ecosystems we can think of. And how does the ecosystem ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
But there's also geothermal energy, but the sun is the source of most energy for most ecosystems we can think of. And how does the ecosystem make use of that energy? How does that get into, how does that get stored within the ecosystem, especially as biomass? Well, it starts with primary producers, which are usually go... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Well, it starts with primary producers, which are usually going to be plants. They can also be bacteria that are able to photosynthesize, that are able to take that energy and create biomolecules that store energy from it. And so these are primary producers, these plants in this diagram. Sometimes you'll see them refer... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Sometimes you'll see them referred to as autotrophs. They are getting their own food from the sun, from this energy. And once again, how is that energy stored? Well, it's stored in these biological molecules. If you were to zoom in into the molecules in this plant, and this is a huge oversimplification, you'll see all ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Well, it's stored in these biological molecules. If you were to zoom in into the molecules in this plant, and this is a huge oversimplification, you'll see all these bonds between these carbons. And to make those bonds requires energy. And if you were to break those bonds, it could release energy. And you might say, we... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And if you were to break those bonds, it could release energy. And you might say, well, where did all these carbons come from that are in this tree? Well, the carbon is coming from the air. Our air has carbon dioxide in it. It has carbon dioxide, so those are the carbons. Maybe let me draw some oxygens. So two oxygens ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Our air has carbon dioxide in it. It has carbon dioxide, so those are the carbons. Maybe let me draw some oxygens. So two oxygens for every carbon. And the whole process of photosynthesis is all about fixing that carbon. Let me write that word down. We are fixing that carbon from a gaseous form, when it's part of carbo... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
So two oxygens for every carbon. And the whole process of photosynthesis is all about fixing that carbon. Let me write that word down. We are fixing that carbon from a gaseous form, when it's part of carbon dioxide, into the structure of the plant, into the biological molecules of the plant. So it's storing that energy... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
We are fixing that carbon from a gaseous form, when it's part of carbon dioxide, into the structure of the plant, into the biological molecules of the plant. So it's storing that energy. Now, it's not a perfectly efficient process. Not all of the energy from the sun is going to be able to be stored. Some of it is being... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Not all of the energy from the sun is going to be able to be stored. Some of it is being reflected. Even the plant itself, as it goes, as it lives, as it reproduces, as its cells divide, some of that energy is used. And eventually, that energy is released as heat. And you're gonna see this trend a lot in thermodynamic ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And eventually, that energy is released as heat. And you're gonna see this trend a lot in thermodynamic systems, that you are taking, you're going from one energy, you're using energy to do some work, but in the process, you are going to be producing heat. But this is just the beginning of our energy flow. Now we can t... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Now we can think about how that energy now flows to the other actors in the ecosystem. So the next phase, and this is a very simplified diagram or ecosystem that we're thinking about. Most ecosystems are far, far, far more complex. Let's think about the characters that would eat the plants, the characters that would ea... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Let's think about the characters that would eat the plants, the characters that would eat the primary producers. And we call the folks that eat the primary producers, we call them primary consumers. So this bunny or this squirrel right over here, they are primary, primary consumers. They consume the primary producers. ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
They consume the primary producers. And why do they consume them? Why does a bunny eat the grass? Well, because it gets energy from those bonds between, in the biological molecules, from those carbon bonds and other bonds. And it's able to use that energy to grow itself, to reproduce, to live, to run around. And it als... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Well, because it gets energy from those bonds between, in the biological molecules, from those carbon bonds and other bonds. And it's able to use that energy to grow itself, to reproduce, to live, to run around. And it also stores some of that energy in its own biomass. And once again, this process is not very efficien... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And once again, this process is not very efficient. Going from one layer of trophy to another layer of trophy, you only have about 10%, 10% of the energy gets transferred or gets stored in the next, gets stored in the next layer. Why only 10%? Well, because not all of the plants get eaten. The whole process of eating p... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Well, because not all of the plants get eaten. The whole process of eating plants, digesting plants, some of the energy gets pooped out, because the primary consumer here, or the consumer, isn't able to get all of it out of the actual biological molecules. And so overall, it's an inefficient process. Now, we're not don... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Now, we're not done yet. We still have energy stored in the biological molecules of this primary consumer that someone might be interested in. And we know that in many ecosystems, there are things that like to eat rabbits or even squirrels. And in this drawing, it will be this fox. And this fox, because it eats primary... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And in this drawing, it will be this fox. And this fox, because it eats primary consumers, we would call it a secondary consumer. A secondary consumer. And you could keep going on with this. If there were some character out here, let's say there's some guy who likes to eat foxes, sets a knife in his hand that he uses t... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And you could keep going on with this. If there were some character out here, let's say there's some guy who likes to eat foxes, sets a knife in his hand that he uses to go after the foxes with. Well, so the fox could go to him. And once again, why is he eating foxes? Well, he wants that energy in that fox, and actuall... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And once again, why is he eating foxes? Well, he wants that energy in that fox, and actually some of them, it's actually not just about molecules. We'll talk about matter in a second. He wants the energy and the matter from the fox to grow and live himself. And so this character would be called a tertiary consumer. Ter... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
He wants the energy and the matter from the fox to grow and live himself. And so this character would be called a tertiary consumer. Tertiary consumer. And if there's no one who wants to eat him, well then he would be considered an apex consumer, an apex predator. And these characters that eat other animals, we've talk... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And if there's no one who wants to eat him, well then he would be considered an apex consumer, an apex predator. And these characters that eat other animals, we've talked about it before, they're called carnivores. But let me just say, he's the apex. And apex, we're really thinking about the top of the food chain. That... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And apex, we're really thinking about the top of the food chain. That's why that would be called an apex consumer or an apex predator. But we're not done yet. Because at some point, all of these characters, whether we're talking about the trees, the bunnies, the fox, this character who likes to eat foxes, they're going... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Because at some point, all of these characters, whether we're talking about the trees, the bunnies, the fox, this character who likes to eat foxes, they're going to die. And that energy just doesn't disappear. And in general, you're gonna see energy is conserved and it flows from one place to another. That energy is th... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
That energy is then going to be used by, it is going to be used by these characters right over here, which we call decomposers. They can take all that leftover energy in that dead carcass or even in the poop and they can make use of it, once again, for them to live, for them to reproduce. And then by breaking that down... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
So it creates this really nice cycle. And the important thing to realize is it comes in as light, that energy gets transferred as we go through the different layers of trophy. And it's not a completely efficient process and a lot of that energy, especially as we, as these organisms live and reproduce and run around, ge... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
Now, we focus a lot on the energy. Let's think a little bit about the matter. And I've already touched on it. But the matter is recycled. There isn't, at least in the way we've set this up, there isn't a new matter that is entering or leaving these ecosystems or being magically created or magically destroyed. As I ment... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
But the matter is recycled. There isn't, at least in the way we've set this up, there isn't a new matter that is entering or leaving these ecosystems or being magically created or magically destroyed. As I mentioned, when you look at a leaf on a plant growing or a tree growing or a leaf of grass growing, that matter is... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
It's coming out of, it's just a different form or maybe the best way to put it, that matter was always there in the form of carbon dioxide. The plant is just using that energy from the sun to fix that carbon from a gas form into a solid form. And it's able to use that energy to form bonds between the carbons in these b... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And the plant can use that energy to grow. And as we've talked about, things that eat the plants or the things that eat the plants can use that energy. And as we talked before, the carbon dioxide comes in. These plants, and maybe this arrow might be a little bit misleading. So let me erase that for now. But we release ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
These plants, and maybe this arrow might be a little bit misleading. So let me erase that for now. But we release oxygen, O2. That oxygen, and we've seen that as part of the photosynthesis process, that oxygen is used by the animals to metabolize these biological molecules. We study that in biology and in respiration. ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
That oxygen, and we've seen that as part of the photosynthesis process, that oxygen is used by the animals to metabolize these biological molecules. We study that in biology and in respiration. And the matter itself, as we say, we have this carbon right over here. When it gets eaten, well then that becomes part of the ... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
When it gets eaten, well then that becomes part of the biomolecules inside of this bunny. And when the bunny uses any of these biological molecules as a source of energy, so it's able to break those bonds through respiration, well then that carbon gets released in the form of carbon dioxide. So maybe this is a better w... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And actually it was already drawn right over here. And so the important thing to realize is that energy is flowing, light from the sun comes in, all this action goes on, and then it gets released as heat on almost every step. But the matter itself, it's always been there. All of the atoms in our body on Earth, it's jus... | Flow of energy and matter through ecosystem Ecology Khan Academy.mp3 |
And if you put that into an evolutionary context, relatedness should be tied to how recent did two species share a common ancestor. And what we're going to try to do in this video is construct a tree for showing how different species evolved from common ancestors, and we're going to do it based on some of these observa... | Phylogenetic trees Evolution Khan Academy.mp3 |
I'm only doing it with five species and five very simple traits. As we'll see or as we'll talk about in future videos, this can be done in a much more complex way, and that's what biologists would do. They would look at much more than five traits, and they would look at molecular evidence, molecular evidence in terms o... | Phylogenetic trees Evolution Khan Academy.mp3 |
So let me write this down. That's what we're going to create. Phylogenetic, genetic tree. Phylo comes from the Greek for group or kind or tribe, and then genetic comes related to the word genesis. How did these things come about? How did the different groups or tribes, or in this case, how did the different species com... | Phylogenetic trees Evolution Khan Academy.mp3 |
Phylo comes from the Greek for group or kind or tribe, and then genetic comes related to the word genesis. How did these things come about? How did the different groups or tribes, or in this case, how did the different species come about? Well, when you're trying to make one of these trees, it's important to realize th... | Phylogenetic trees Evolution Khan Academy.mp3 |
Well, when you're trying to make one of these trees, it's important to realize that this is a hypothesis, but you're, like always, trying to come up with the simplest hypothesis that can explain the observations that you actually see. And when we look at these, at least the species that we have listed here, it looks li... | Phylogenetic trees Evolution Khan Academy.mp3 |
The lamprey is the outgroup, and a lot of times when you need to construct a phylogenetic tree, they might provide you something with something that is clearly an outgroup. Here it doesn't have any of these observable traits. Sometimes if we're looking at genetic differences, it might have the largest number of genetic... | Phylogenetic trees Evolution Khan Academy.mp3 |
And so it makes sense, the simplest hypothesis is its common ancestor is most distant into the past with everything else. And so let me start to draw this tree. So I am going to put deep into the past, so deep into the past, there is a branching out point where you have the common ancestor of the lamprey and everything... | Phylogenetic trees Evolution Khan Academy.mp3 |
So eventually, that common ancestor, and there's many, many species along the way, and eventually we get a lamprey in present time. In present time. And so the next thing to think about is, all right, well how did everything else end up branching? Well, what's common about everything else that maybe wasn't common about... | Phylogenetic trees Evolution Khan Academy.mp3 |
Well, what's common about everything else that maybe wasn't common about the lamprey? Well, one common thing is we see that everything else, at least that we have listed here, have jaws. And so it's reasonable to say, all right, we have this common ancestor, this between the lamprey and everything else at this branchin... | Phylogenetic trees Evolution Khan Academy.mp3 |
And then it branched off into multiple species, and one of those species must have evolved jaws. So let me put jaws right over here. So jaws right over there. And jaws, that's called, jaws are considered a derived trait. This ancestral species at this root did not have jaws, we're assuming, but at some point, they evol... | Phylogenetic trees Evolution Khan Academy.mp3 |
And jaws, that's called, jaws are considered a derived trait. This ancestral species at this root did not have jaws, we're assuming, but at some point, they evolved and they stuck around because they proved to be favorable in certain environments. Or it could have even been things like genetic drift, who knows, but I'm... | Phylogenetic trees Evolution Khan Academy.mp3 |
So let's see, let's see if we can classify everyone else. So now out of the four, so let's actually cross out the lamprey just for simplification, since we've already classified that character. Now of everyone else, we've already thought about, everyone's got jaws, so now let's go to the next most common trait. So, and... | Phylogenetic trees Evolution Khan Academy.mp3 |
So, and actually let me cross out the jaws too, just for, keep things simple. So I can do that a little bit cleaner. So I'm gonna cross out the jaws. And now let's see, the most, the next most common trait is, are the lungs, but not every species that we have left has lungs. The sea bass does not have lungs. It does no... | Phylogenetic trees Evolution Khan Academy.mp3 |
And now let's see, the most, the next most common trait is, are the lungs, but not every species that we have left has lungs. The sea bass does not have lungs. It does not breathe air the way that animals that live outside of the water breathe air. And so they, the next, the next point of divergence must be between the... | Phylogenetic trees Evolution Khan Academy.mp3 |
And so they, the next, the next point of divergence must be between the sea bass and everything that we have left over. So let me draw that. So, and once again, I said must be, this is a hypothesis. I think it's a reasonable hypothesis. So let me draw that. So this is the sea, sea bass. And there's a common ancestor be... | Phylogenetic trees Evolution Khan Academy.mp3 |
I think it's a reasonable hypothesis. So let me draw that. So this is the sea, sea bass. And there's a common ancestor between the sea bass and everything else, and the antelope, the bald eagle, and the alligator. And at some point, that common ancestor diverged into multiple species, and one of those, one of those chi... | Phylogenetic trees Evolution Khan Academy.mp3 |
And there's a common ancestor between the sea bass and everything else, and the antelope, the bald eagle, and the alligator. And at some point, that common ancestor diverged into multiple species, and one of those, one of those child species must have evolved lungs. So lungs must have evolved at some point. But we're a... | Phylogenetic trees Evolution Khan Academy.mp3 |
But we're assuming that that wasn't, that wasn't on this lineage for the sea bass. And once again, I'm just trying to find the simplest explanation. There might have been some situation where maybe lungs evolved and then, de, or then went away at some point. You reverted to an ancestral form. But we like to go with the... | Phylogenetic trees Evolution Khan Academy.mp3 |
You reverted to an ancestral form. But we like to go with the simplest explanation. This is a property that biologists will also often call parsimony. And actually, let me write this down. Parsimony, which in everyday language means cheap. If someone tells you you're parsimonious, it's a nice sounding word, but it mean... | Phylogenetic trees Evolution Khan Academy.mp3 |
And actually, let me write this down. Parsimony, which in everyday language means cheap. If someone tells you you're parsimonious, it's a nice sounding word, but it means that you are cheap. But parsimony in this context say, hey, we're trying to, we're trying to be cheap with complexity. We're trying to be as simple a... | Phylogenetic trees Evolution Khan Academy.mp3 |
But parsimony in this context say, hey, we're trying to, we're trying to be cheap with complexity. We're trying to be as simple as possible in our explanation of what's going on. But anyway, let's go back to what we were doing. So we've already put into consideration, we have already talked about the sea bass here, and... | Phylogenetic trees Evolution Khan Academy.mp3 |
So we've already put into consideration, we have already talked about the sea bass here, and we have already talked about lungs. All right, so what do we have left? So we have to talk about the antelope, the bald eagle, the alligator, and gizzard, and fur. All right, it looks like the bald eagle and alligator have gizz... | Phylogenetic trees Evolution Khan Academy.mp3 |
All right, it looks like the bald eagle and alligator have gizzard, the antelope has fur. Oh, and actually, we haven't talked about the bald eagle and feathers as yet either. All right, so it is possible. So let's make the next thing between, well, we could do it this way. And once again, I'm trying to do this in real ... | Phylogenetic trees Evolution Khan Academy.mp3 |
So let's make the next thing between, well, we could do it this way. And once again, I'm trying to do this in real time, something that seems, so let's make a branch here. And let's say that that is the branch for, let's say that's the branch for the bald eagle. Let's say B eagle. That's the branch for the bald eagle. ... | Phylogenetic trees Evolution Khan Academy.mp3 |
Let's say B eagle. That's the branch for the bald eagle. Let's see if I can construct one that'll explain the differences between the bald eagle, the antelope, and the alligator. Well, the bald eagle and the alligator have something in common. They have a gizzard in common. So let me make a branching point, make them a... | Phylogenetic trees Evolution Khan Academy.mp3 |
Well, the bald eagle and the alligator have something in common. They have a gizzard in common. So let me make a branching point, make them a little bit closer than the bald eagle is to the antelope. So let me do that. So let me put the alligator there. And then I'm gonna talk about when we get these derived traits. So... | Phylogenetic trees Evolution Khan Academy.mp3 |
So let me do that. So let me put the alligator there. And then I'm gonna talk about when we get these derived traits. So that is the alligator. And obviously I could have written the alligator on this side and the bald eagle on that. So I could rotate at any one of these branching points. And then what we would have le... | Phylogenetic trees Evolution Khan Academy.mp3 |
So that is the alligator. And obviously I could have written the alligator on this side and the bald eagle on that. So I could rotate at any one of these branching points. And then what we would have left is the antelope. Now let's see if I can account for all of these derived traits. Antelope. All right, so we have th... | Phylogenetic trees Evolution Khan Academy.mp3 |
And then what we would have left is the antelope. Now let's see if I can account for all of these derived traits. Antelope. All right, so we have the common ancestor of the sea bass, the bald eagle, the alligator, and the antelope right over here. We have a branching point. At some point, the lungs, where we are hypoth... | Phylogenetic trees Evolution Khan Academy.mp3 |
All right, so we have the common ancestor of the sea bass, the bald eagle, the alligator, and the antelope right over here. We have a branching point. At some point, the lungs, where we are hypothesizing, evolve in this branch. And then this branch, well, let's say that this branch, this is the common ancestor between ... | Phylogenetic trees Evolution Khan Academy.mp3 |
And then this branch, well, let's say that this branch, this is the common ancestor between the antelope, alligator, and bald eagle. And a common ancestor of the bald eagle and alligator, they have to get the gizzard. So let's put the gizzard down right over here. This is where the gizzard, this is our hypothesis. Do t... | Phylogenetic trees Evolution Khan Academy.mp3 |
This is where the gizzard, this is our hypothesis. Do that same colors. So that's the gizzard. Gizzard right over there. And so everything that descended from that ancestor that had the gizzard, well, they're going to have gizzards. That's what we're assuming. But once again, that can be lost. | Phylogenetic trees Evolution Khan Academy.mp3 |
Gizzard right over there. And so everything that descended from that ancestor that had the gizzard, well, they're going to have gizzards. That's what we're assuming. But once again, that can be lost. This is a hypothesis. And so we have accounted for the gizzard. Let me cross that out. | Phylogenetic trees Evolution Khan Academy.mp3 |
But once again, that can be lost. This is a hypothesis. And so we have accounted for the gizzard. Let me cross that out. So we have accounted for the gizzard. And so let's see, we have to account for the feathers. And the bald eagle is the only one that has feathers. | Phylogenetic trees Evolution Khan Academy.mp3 |
Let me cross that out. So we have accounted for the gizzard. And so let's see, we have to account for the feathers. And the bald eagle is the only one that has feathers. So let me put that here. So at some point, you have a common ancestor of an alligator and a bald eagle. It branches off into multiple species, one of ... | Phylogenetic trees Evolution Khan Academy.mp3 |
And the bald eagle is the only one that has feathers. So let me put that here. So at some point, you have a common ancestor of an alligator and a bald eagle. It branches off into multiple species, one of which gets a feather or gets feathers. And once again, that could have branched off into many, many things, because ... | Phylogenetic trees Evolution Khan Academy.mp3 |
It branches off into multiple species, one of which gets a feather or gets feathers. And once again, that could have branched off into many, many things, because we know that the bald eagle isn't the only species with feathers. But the bald eagle for sure is a species that has feathers. And let's see, so we've accounte... | Phylogenetic trees Evolution Khan Academy.mp3 |
And let's see, so we've accounted for the feathers now. Feathers. And now we just have to account for the fur, the fur of the antelope. And so we don't know where this could have happened. We might want to look for more evidence to come up with a good hypothesis. But someplace along this right branch, we could put the ... | Phylogenetic trees Evolution Khan Academy.mp3 |
And so we don't know where this could have happened. We might want to look for more evidence to come up with a good hypothesis. But someplace along this right branch, we could put the fur. And so there you have it. This is actually a reasonable phylogenetic tree. I practiced the practice of parsimony to come up with th... | Phylogenetic trees Evolution Khan Academy.mp3 |
And so there you have it. This is actually a reasonable phylogenetic tree. I practiced the practice of parsimony to come up with the simplest explanation. But there are more complicated explanations. And we don't know, some of those more complicated explanations could very well be true. But from this, we have a very qu... | Phylogenetic trees Evolution Khan Academy.mp3 |
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