 So, really, Charles Darwin is quite a famous young fella who pretty much came up with an explanation for how evolution can happen, how allele frequencies can change. What is a mechanism by which this can take place? Now, there was a lot of evidence at this point in history. There was a lot of evidence that indicated that there was stuff going on. And in fact, there were definitely conversations happening about, dude, why is it that there are fossils that we find buried in the dirt that are of critters that aren't here anymore? Where did they go? What happened to them? Why is it that we see these various forms of critters that are kind of familiar but a little bit different? There was a lot of evidence and a lot of conversation that there were evolutionary processes at work, but people really didn't have an idea for how it happened. So, oh boy, Darwin, he did all sorts of great adventures. And if you are interested in the process of science, like following his path to figuring out what he figured out, it's really pretty interesting. But let's talk about the observations that he made in his travels that ultimately led him to drawing the conclusions that we will talk about. So, he had several observations. And the first observation that he had is that populations of critters exhibit great variation. And this is probably something that is really intuitive to you. You're probably thinking, well, of course, they show great variation because, yeah, we see it all over the place. This is one population of ladybugs. They're all the same species, but look at these guys. I mean, we've got multiple spots. We've got dark, reddish. We've got no spots. We've got light. I mean, there's just a great deal of variation in this population, and they all can make babies with each other. And you can imagine that, you know, why and are there possibly advantages of this? Here's a population of froggies. Again, this is all the same species of frog collected from, I don't know where, probably they're all dead now. But they, like, look at that variation. Lots of different colors. That's the first thing that Darwin came up with. That was his first observation. Wow, these populations of critters have a lot of differences amongst them. Now take a second. Where do the differences come from? Why? Why are they different? Well, hopefully, from your previous experience in this course, hopefully you know, you can speculate on some sources of variation. Number one, meiosis dog pounds, sexual reproduction dog pounds, and then, ultimately, mutation dog pounds, mutating DNA, an oops, oh, gee, there was supposed to be a C there instead of a G in that sequence of DNA, and now I've coded for a different protein or no protein at all, and now I have a different phenotype than I started with. And random mutations absolutely happen, and lots of mutations don't matter. Like, who cares? There's no variation that results from them, but sometimes there is variation, and other times there's death. Like, there are some mutations, as we well know, where you aren't even going to make it past the zygote stage if you've got that problem going on like you're done. And that's fine, but all these different crazy cool colors, awesome. Critters have lots of variation. Okay, let's take a look at his second observation. His second observation was holy overpopulation. What? He observed it all over the place. More babies were born than could even remotely possibly survive. Look, what is that you might wonder? This is the glory night of sponge life, because this is the night where how does it happen? But the moon is right, the stars are right, the temperature is right, and all the sponges in the ocean are like, hmm, it's a good night tonight to squirt out all our sperm and eggs and out go all the sperm and eggs. And seriously, like, that is a sperm and egg cloud. All of the sponges are doing this. Now, one sponge throws out like bajillion, funnillion, gazillion, bazillion sperm or eggs. One. And then all the other sponges that are surviving in the ocean are doing the same thing. If all of them survived, what's going to be a sad story? Here's some more. Like, this looks like actually some kind of a, maybe that's a clam squirting out its stuff into the ocean, hoping that the eggs find their sperms and make happy little zygotes that become little larva and grow up into grown-ups. But all those are babies. And, dude, that's crazy overpopulation. I think I might have one more. Yeah, holy cloud of mad gametes, it happens. And then all the fish are like, dude, this is the smorgasbord of ever. And they come and they try to yumptialize all the baby zygotes that are floating around in the ocean on this glorious night. Wow, overpopulation. Thank you, Darwin. We do believe you. Critters overpopulate. Here's his third observation. They're all different. Way too many of them are made. And you know what? There are limited resources. Limited resources. Because think about it. 8 billion baby sponges and how many, like, is there enough room on the ocean floor for 8 billion new sponges? Nope, not enough room. There's not enough food for 8 billion new sponges for every one sponge that exists. If 8 billion really did, like, survive, that's going to be a sad, like, crazy scene. So, whoa, we've got some weird stuff going on here. They're all different. There's bajillions of them. And there is absolutely no way they're going to all survive. So, how do we decide who's going to live? Go ahead and just think on that. I'll come back and I'll tell you all about it.