Have you ever wondered why you don't have thick hair covering your whole body like a dog, cat or gorilla does? Humans aren't the only mammals with sparse hair. Elephants, rhinos and naked mole rats also have very little hair. It's true for some marine mammals, such as whales and dolphins, too. Scientists think the earliest mammals, which lived at the time of the dinosaurs, were quite hairy. But over hundreds of millions of years, a small handful of mammals, including humans, evolved to have less hair. What's the advantage of not growing your own fur coat? I'm a biologist...