To avoid confusions, let's get rid of this picture and start fresh. And on the other hand, we will see that, although some other structures might look very different and perform different functions, they can be related to each other. And so in this video we will explore why certain structures, which might look similar and perform same function, did not necessarily mean that they are related to each other. And in fact it turns out, surprisingly, it's these two structures are more closely related than these two, or these two.

But it turns out that in reality, they are not as closely related to each other. They look very similar and they're both used for swimming, so we could say, 'Hey, maybe they are very related 'to each other.' And similarly, if you look at the wings of the bat, let me use a different color, wings of a bat, and the wings of, say, an eagle, again, both are used for flying, they look kind of similar, we might say they are related to each other. For the dolphins we don't call them as fins, we call them as flippers. In these pictures, we might look at the fin of the shark, and say they are very similar to the flippers of a dolphin.

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