 Remember these guys? I mean, especially these little guys right here. Awe. So hopefully this looks familiar to you. And I'm going to use this little clatogram that we built to remind ourselves of the different processes of evolution. Often when we think about evolution, we think about speciation. And we talked about this a lot last week. We talked about how we actually are sharing. There's an ancestor long, long time ago that we actually had in common. We shared a recent common ancestor, humans and whales. Really? Wow. And you can imagine, like what did that ancestor look like? And we can say, well, we're pretty sure that that ancestor probably had mammary glands because both these little boys and these little boys have mammary glands. That's a characteristic that they share in common. And if both the offspring have mammaries, then probably their ancestor species also had mammaries. So what we're seeing right here, this process that goes from this ancestor A to a population of whales in the current time and a population of boys in the current time, that process is speciation and it's macroevolution. So I'm going to write it in black so that you know that I'm talking about these black lines right here. But it's an example of macroevolution. And really, it's speciation. But the question that you should be asking, and hopefully the question that we'll get more and more clear as we talk about this further, something has to power that. And the something that provides the fuel or the oomph, oomph. The something that provides the oomph for macroevolution is microevolution. And microevolution is nothing more than a change in allele frequency, what? In a population of critters. So back in the day, whenever it was that we shared an ancestor, our most recent common ancestor that we shared with old boy whales over there, back in the day, that population of critters had a certain gene pool and a certain frequency of alleles. And then that allele frequency that was present back in the day changed. And I mean, we can see phenotypic evidence of the change in our two living populations of critters that came or were given risen to. This population gave rise to both of those populations. But we can see that, yeah, it would make sense that the allele frequency would change. So let's talk about allele frequency. What is it? And actually, even how can you calculate it? Because guess what? You can.