We are used to the fact that men grow hair on their heads and faces. And that some men even dare to grow hair on their chests — much to the horror, it seems, of most girls.
We also know that male hair growth is in part related to testosterone levels — or at least the testosterone level at some critical point in their development — as well as genetics.
So why is it that even the hairiest of men don't grow hair round where their shirt collar goes? (There are a few very, very hairy men who do grow hair under their collars, but they are unusual.)
It seems unlikelky that the lack of hair is due to collar abrasion. The area is totally devoid of hair and there is no sign of hair regrowth if collars are not worn. The collar also seems not to affect hair growth in those very hairy men who do grow hair on their necks.
This really does seem to be a genuinely hairless area.
Can anyone explain why this is the case and what evolutionary advantage it might once have had?
Or perphaps to put it another way ... why is facial and chest hair selected for, but neck and shoulder hair mostly isn't?