 We're back. And this time we've got a selection of critters across the top. You will notice that I got us a very lovely butterfly, a very adorable pair of small humans. What? How cute are those little clowns? And then we had to have a clownfish to go next to the clowns and a couple of whales. Your job is to build an evolutionary tree out of these critters. Even though we tend to put the most advanced and perhaps cute critters on the left side of the trees, that is just actually, I'm totally putting them on the left side, but normally we put them on the right side, which is, I hope that doesn't confuse you. It's because I was trying to make my tree like, I was trying to draw my picture from the left side instead of the right side. I messed everything up. No, it's all good. It doesn't matter how you put it, as long as the relationships are the same. So I'm going to throw my little cute small people up in the top left corner. And the only thing that matters is that you are going to help me decide which of these remaining three animals, they're all animals, right? Which of these remaining three animals is most closely related to those little clowns? Well, hopefully you would look at that and you'd be like, they are clowns and this is a clownfish, but that doesn't mean that they're most closely related. Whales are actually mammals, right? And so the mammals, the whales are more closely related to my little clown children than to the clownfish. So look at this. We could totally make a little line. Here's boys, here's whales, and they share a most recent common ancestor. And do you agree that we could throw some things on there? Since they're both mammals, we could throw on there that they have memories and they have hair. Awesome. Because that just tells us, dude, they're mammals. And even though you might be like, I'd like the whale to go with the clownfish or the boys to go with the clownfish, whichever you prefer. In fact, if you think about it for a while, fish do not have memories. They do not have hair. They are cold-blooded. They have gills. They've got different body setups. They don't breathe air. They breathe air, oxygen out of the water. There's a million things that are going on with fish that are very different than what's going on with whales. But if you have these two choices left, all of them are animals. Who are you going to put next? Boys and whales are now in a group called mammals. I'm going to go on the clade next or on the tree next. If you are thinking, dude, the fish, the clownfish, what is the characteristic that all of those guys share in common? The clownfish, the boys, and the whale all share what in common. They do have a common ancestor. And do you agree that they're all vertebrates? They all have the vertebra column, right? Now, I've already told you that all of these guys are animals. And so we can throw the butterfly on our tree and know that there are characteristics that all animals have in common. So let's go ahead and map out that. I'm actually going to tell you what the characteristic is, even though it might not make a whole lot of sense right now. This is so cool because you know all about this. All animals have a characteristic in common and it's that they all have a blastula. And we're going to talk about this often. They all have... What is a blastula? What? Ready? During, like, after fertilization, sperm, egg, join, make a wet, the zygote, the zygote goes through what process, mitosis, to form like you. And we know this. Like, how many times did you get asked questions about the human life cycle? All animals have a similar life cycle. And one of the stages that all animals share is that they actually sperm plus egg make zygote. Zygote divides into a hollow ball of cells called a blastula. So the fellas up there in the top left corner, they used to be blastulas. The whales used to be blastulas. When they were in their momma's bellies, the whales were blastulas. The fish, when it was in a little fertilized egg, had a blastula stage and a butterfly had a blastula stage. Can you believe there's blastula butterflies? That's so cool. So the blastula is the characteristic that they all share in common. Now, who's the most recent common ancestor of the boy and the whale? Ancestor A. Boy has Ancestor A. Whale has Ancestor A. The most recent common ancestor between these guys is Ancestor A. They both also share Ancestor B, but it's not a recent. It's not the most recent common ancestor. They have a more recent common ancestor. And the more recent your common ancestor that you share with somebody, the more closely related you are to them. So Clownfish, awesome. The Clownfish shares the most recent common ancestor, B, with both these guys. You might. Oh, my gosh, I have to put this into a clicker question. Who is more closely related to the Clownfish, the whale or the boy? And look at most recent common ancestors and you will see that, you know what? Boy and Clownfish share Ancestor B. Whale and Clownfish share Ancestor B. Do you know what that means? The whale is equally related to the Clownfish as the boy is related to the Clownfish. You might be like, no, dog. The whale looks like a fish. It has to be more closely related. It is not. They're equally related to each other. And then there's the poor little butterfly that that ancestor was long, long ago, back when Blastulas were new. And they made their first Blastula, but they had that ancestor in place. How neat is that? All right, that's cool. Now I'm going to give you a cladogram example, an actual tree without pictures, and then analyze it so that you can practice.