Whales! They are descended from land mammals who decided that, actually, the ocean was a better idea after all! As they became more comfy in their new aquatic home, they realized they didn't need all those extra land-based body parts. Back legs? Nope! Arms, nah, let's try out some flippers! The last thing to go was their land-based thrice-a-day coffee habit! Can't drink coffee underwater, but giving it up means whales had to change the way they sleep. And thus was born the famous "whales can rest half of their brain at a time" adaptation. Who knows, give us a few million years in the swimming pool, and humans might be able to match the whale's amazingly adapted naps! Until then, we'll take three more coffees, please.