Hair parts where the hair grows in a different direction.
For all the money we spend on perms and conditioners, hair is an oddly useless human feature. It offers little protection or warmth, even in the truly rug-chested.
Body hair's main function is to enhance skin sensation. And though they may offer some shielding from sunrays, your 100,000 to 200,000 scalp hairs are mostly there to show off your reproductive health (which is why both sexes tend to find long tresses sexy).
The shape, texture and direction of hair are determined by the follicle, from which the shaft grows wavy, curly or straight, and in any direction. The hairs on a patch of skin generally point in the direction of their neighbors. The paths they make are known as hair streams, on the body and scalp alike. Everyone has their own unique pattern of streams, but some prominent features, like the line in the scalp, are shared by all.