Photo: Anaa Yoo (Flickr)
Hair vs Fur
The main difference between hair and fur is where it grows, not what it’s made of.
Hair length is a trait that’s specific both to you as an individual, and to your species. So you have long hair on your head and short hair on your arms, while a deer has short hair all over. Also, unlike hair, fur includes a layer of finer, shorter denser hairs, the underfur, through which longer, coarser, more thinly distributed guard hairs extend. So how come humans don’t have fur all over our bodies?
Hair Doesn’t Fossilize
Most of what science knows about evolution comes from fossils, and hair doesn’t fossilize. This means that we don’t know when or why hair and fur evolved. One theory is that fur evolved because mammals are warm-blooded and hair is a good insulator.
If you’re going to spend all this energy heating yourself up, you want to be efficient about it. A different theory is that hair enhances the sense of touch–likes whiskers, for example.