Great question! Humans have evolved to be practically bald, which many scientists believe was a combination of some basic sexual selection with a biological effort to rid our bodies of hair-based parasites. We all still have hair follicles all over our bodies, but male humans often grown thicker, longer facial hair than females. It turns out that this is largely hormonal: male facial hair follicles aggressively respond to testosterone production.

Male facial hair, like human hairlessness, is also likely a product of sexual selection. Many male monkeys, such as the lion-tailed macaque and the bearded tamarin, also show dramatic facial hair. This is likely because the ability to grow facial hair is the sign of a healthy male, and makes females more open to reproducing with these males. The same could be true for humans! Of course, the field of evolutionary biology is still rapidly developing, and there is much to learn. You could be the one to figure it out!

There was a popular book long ago, about us, called "The Naked Ape".

Maybe we have facial hair because we have share some very ancient ancestors with apes, and they have facial hair.

Men have more facial hair than women because men have more testosterone, and the hair follicles on the face respond strongly to testosterone.