 I mean, in a lecture entitled Evolution, does it really take seven clips before you finally get to the definition of evolution? Yes, yes it does, and that's okay. So, Evolution, you probably know by now that I'm actually super interested in all the tiny stuff. I love knowing how cells do what they do and how that ultimately creates what we see. And Evolution represents the concept, the idea, the topic in this class represents our transition from little itty-bitty things and little itty-bitty processes to big picture, like holy crap, big, like crazier, big, bigger than our little brains. We can't even begin to imagine how big we're talking when we look at the overall process of Evolution that has happened and given rise to such grand diversity that we see on this planet. But of course, because I love the little things, like I want to know, like, how'd that happen? How did that, like really, how'd that happen that dinosaurs, a kind of dinosaur actually gave rise to a bird? How'd that happen? And so my first definition that I'm going to give you of Evolution is very molecular, very genetic, and that is this, Evolution is nothing more, nothing more than a change in allele frequency in a population over time. And there are a couple of pieces of this that probably deserve a little extra attention. I've found my colors and I have pink now, so that makes me happy. And so the first thing that we have to define is this concept of allele frequency. What? Allele frequency. Well, okay, never mind. That's the second thing that we're going to deal with. The first thing we're going to deal with is the fact that Evolution happens in populations. And I think we've already talked about this because it's such a huge misconception that I targeted and, like, asked you 800 questions on the exam about this. Evolution does not happen in an individual. And pull your brain back to the very beginning of this class. And we talked about, we actually defined a population. What is a population? It's a group of critters that can make babies. Often the population is, like, a species. Like, so they're all the same species, but the word species, it gets crazy if we start thinking that through. So if you just consider a population as a group of critters that can make babies with each other, then you're good. Because populations are what actually evolve. Individual critters or people do not evolve. Populations evolve when their allele frequency changes. So visualize this for just a second. Think about our class. Imagine that we considered a trait like tongue rolling, like that. And we imagined, okay, I can't remember what alleles we use, but we have maybe big R and little R. And big R is the dominant rolling trait, I mean allele, and little R is the recessive non-rolling trait. Like that. Now, we should totally do this in class. We could calculate the allele frequency in our class, I'm so going to do it. I got to make a note to myself that I'm going to make a clicker question like right now so that we can do this in class. So I'm a roller, obviously, and I have a kid who is a non-roller, and so I actually had to have a little R to donate to him, but I'm a roller, which means that I also have to have a big R to enable me to roll, right? So I'm a heterozygous, got it. That means I'm donating one big R and one little R to the population. Let's look at my little kid who cannot roll his tongue. We're going to say that he is little R, little R, because he has to be. Now, if he and I were a population, we could calculate our allele frequency. All we'd have to do is say, hey, we have four total alleles, one out of four, our big R, which is what, 25%, and three out of four, our little R, which is 75%. Now, someone came into our house and was like, if you can't roll your tongue, you're out of the population, then that would be extremely traumatic for me, and I really don't like thinking about that analogy. It was quite horrible. But if that happened, bye-bye, little R, then there's going to be my allele frequency just changed in my population. Are you good with that? I mean, hopefully you're not good with that at all because it's quite horrifying, but the allele frequency changed in your population, evolution occurred. This is specifically known as microevolution, and microevolution is that simple. You end up with a change in allele frequency in your population over time. Now, changes happen all the time, and changes can be totally random, and we're going to talk about different mechanisms for microevolution, like how it actually happens. If microevolution happens enough and a population experiences reproductive isolation, I have to write it down, that says reproductive isolation, then you can have something known as macroevolution. Evolution. Okay, ready? Macroevolution takes place. You have a population with a whole bunch more than two people, so I can't give you, I can't draw you pictures. You have a big old population, and let's say the population splits. Like that mountain range comes up in the middle of the population, and half of them are on this side, and half of them are on this side. That's reproductive isolation. Those guys aren't going to make babies with each other anymore. However, they're totally going to have their own allele frequency dynamics in their own populations. They've been reproductively isolated, and they're changing. Microevolution is happening in their population. That can lead to speciation, the formation of a new species. Let's put reproductive isolation and macroevolution equals speciation, or macroevolution, speciation, the formation of a new species. It's not directed, and it's not like they all sit down. You know they do this. They all sit down and go, you know, I think it would be a good time for us to form a new species. You know, these guys, like, we don't really want to be associated with them anymore. Okay? All right, that analogy just died. But the point is that this, if you have these characteristics, you can make new species. Ready? Don't forget this part, because it becomes sort of like, no, that's not possible unless you remember I had to pick the right color, this piece. It's over time. And we're not talking over a couple of years, although microevolution totally happens in populations in, like, observable generations. Like, we can totally see it happening in a population. But macroevolution is, like, jillions and jillions and jillions of years for it to happen. I think that's all I have to tell you. And what was I going to go do? Oh, I was going to go make a clicker question so that we can count up our allele frequency. Okay, I'm going to go do that right now. If I can find my place to push pause. Bye-bye.