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Convergent Evolution

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Convergent evolution, also called parallel evolution, is a type of evolution in which two unrelated species develop similar traits due to similar environments or selective pressures. These similar traits are called analogous traits. Though these species look alike, we cannot call them related because they descended from different ancestors.

One common trend seen in evolution is something known as converging evolution. some people will make a distinction from this and parallel evolution but a lot of people just consider them the same thing. And the basic idea of both convergent and parallel evolution is when two different organisms, two different species that are not closely related wind up looking similar. And it's not because they come from a common ancestor, it's because simply they live in similar environments or they're under similar kinds of selective pressure. What are some of the examples of these?

For example, there's European rabbits in Europe that hop around in the field collecting their little seeds or whatever it is that rabbits eat. And in South America there's something called the mara. We take a look at the picture of the rabbit and the mara. you'd say, hmm they look pretty similar. Kind of longer forelegs, their back legs are good for hopping and jumping. they got slightly a long, well, really long and not quite so long. But it turns out they're not very closely related at all. In fact, this is a kind of rodent. Its closest relative is a guinea pig, and that's a very different group from rabbits. Why do they look so similar? Because they live in similar environments. There are no rabbits where the mara lives so there's nothing occupying that environment or niche. So just like the rabbit had these adaptations to best suit its needs, the mara under similar forces wound up doing and finding similar solutions.

Now this leads into a discussion of what's called analogous traits. These are similar traits that are independently evolved in unrelated species as distin- distinguish from homologous traits. So that's very these similar traits that are derived in related species. For example I have a hand that I can use for picking things up, for grasping things and climbing trees. Bats can use this same limb the front top arm or leg but they've adapted them into wings. They've greatly elongated fingers. The bat tries to grab you with all of its phallanges these bones here, it's not going to work so well. Alright? It can't climb trees as well as I can. It can't open up door knobs as well as I can.

Now, in an example that you might be familiar with of convergent evolution are sharks and dolphins. They have very similar or analogous traits. they have a dorsal fin, they have this torpedo shape, they have side or pectoral fins. they've got all these fins, they're looking very similar. Why is that? Because this is a good shape to go through water. If you're a big cube, you don't swim so well. If you want to swim at 20, 30 miles an hour, you'll look like this. That's why this is called a torpedo shape. Why is it called a torpedo shape? Because we make torpedoes that look kind of like this. Why? Because we want torpedoes to go fast in water. Sharks and dolphins are not closely related t all. They're separated by millions and millions of years. Probably well over couple of hundred million years if I remember right. But dolphins and sharks wind up often people will mistake one for the other. And I hope that you're mistaking a dolphin for a shark and not vice versa when you're at the petting zoo.