Hairiness in humans

I remember seeing the so-called “Mexican Wolf Boys” (who are covered with fur-like hair!) on Discovery Channel a while back. That got me thinking about the great disparity between individuals with regard to body hair. I have known some guys (Italian and Turkish) who actually seem to approach the “wolf boys” in hirsuteness. Other guys have virtually none! Are there some nationalities that tend to be hairier in general, or is it just an individual thing? What purpose, if any, does body hair serve in modern day humans anyway?

It doesn’t have to serve a purpose; it just has to be non-lethal. From an evolutionary standpoint.