How Evolution in Isolation Works


Announcer: Welcome to Stuff You Should Know from howstuffworks.com.

Chris Pollete: Hey there, welcome to the Podcast. I'm Chris Pollete; I'm one of the editors here and with me, as always, is staff writer, Josh Clark. Hey, Josh.

Josh Clark: How's it going, Chris?

Chris Pollete: Doing okay. I thought we would talk about what happens when animals evolve in isolation and basically it starts with the theory of evolution and how we're all related.

Josh Clark: Exactly. Yeah, and like you said, you hit upon this in theory, I think we should say that not everyone subscribes to evolution but if you're a scientist, you most likely do. There are a few ways to go about evolving and one of them is through evolution and isolation. For that to happen, you have to go through a speciation event, and what that is, just when one species becomes two or more species. For example, bears. You want to talk about bears?

Chris Pollete: Sure. We can talk about bears.

Josh Clark: Okay. Well, the black bear is the parent species of the polar bear. It makes sense if you think about it. They're bears, right, so surely all bears are related but how do polar bears become white; why are black bears still black? I think evolutionary biologists tend to believe that it was because of a parapatric a speciation event and parapatric speciation occurs when a species becomes so spread out geographically that members in different areas or living in different environments, undergoing different experiences, so the black bear up north had a fur coat that stood out like a sore thumb against the white landscape, the snow-covered landscape so they evolved to be white. That's not enough. That doesn't cover speciation entirely. For speciation to be complete, you have to go through reproductive isolation and this just means where the members of the species no longer can produce offspring. It can be because they develop different genitailia, it can be because they've developed different times of the year to mate, different locations to mate in, either way, if reproductive isolation occurs, a speciation even has taken place.

Chris Pollete: Okay. So, basically they just have to be different enough where they're no longer able to reproduce with one another and then they gradually become a different species all together.

Josh Clark: That's exactly right. And there's also some other really interesting aspects to evolution. One of them I know you know a lot about and that's the evolutionary bottleneck, right?

Chris Pollete: That's true. This is when a group gets completely or I guess nearly completely cut off from the main group so they are reproducing only with one another. It's like a bottleneck. If you think like a soda bottle but, you know, that can cause some problems because if there's a genetic defect, it can be passed down from generation to generation. You mention in the article a group of Amish people in Pennsylvania who had smaller than - who had a trait for smaller than normal brains, microcephaly -

Josh Clark: Um-hum.

Chris Pollete: And, you know, that can be fatal so obviously in this case, this very small group of people, having that trait be passed down, was fatal to that group.

Josh Clark: Not a desired trait either.

Chris Pollete: No, definitely not. But, you know, Josh, one of the other examples that you used in the article that I thought was really cool was the iguanas that were displaced by Hurricane Maryland.

Josh Clark: Yes.

Chris Pollete: And that's sort of evolutionary bottleneck and it's also an example of a different kind of speciation, allopatric which is they're cut off by a geographical boundary, in this case, they're on an island separated by - the main group by water - and this small group of iguanas floated from Guadalupe to Anguilla. And I think that's really cool because it's a completely scientific study. There are no - or there were no iguanas on Anguilla before this happened so it's -

Josh Clark: Yeah, it's a completely natural experiment.

Chris Pollete: Right, right. And it wasn't forced. They just happened to notice that these iguanas are going to go here so they found out - we're going to find if they'll be a bottleneck and also the island rule, which is funny - that is an island but the island rule would give them a chance to see if these iguanas will grow larger or smaller as the result of being cut off from the main genetic body of iguanas so it's going to give scientists a chance to see evolution up close and personalize it.

Josh Clark: Ironically, it was a gift from God to conduct a natural experiment on evolution.

Chris Pollete: Well, there you go.

Josh Clark: But you can read all about this in, "What happens when Animals evolve in Isolation," on howstuffworks.com.

Announcer: For more on this, and thousands of other topics, visit howstuffworks.com.