Our ancestors probably were entirely fur-clad? I certainly do not claim to be an expert..however I have heard the theory that head hair acts as protection (in lieu of a hard hat)...can also help retain heat..this makes a lot of sense if you live in the far north or far south...however...since the DNA "chain" seems to show that we all evolved from Africa? idk...theory regarding armpit and pubic is for lube? I cannot argue with these scientists...as long as my woman has some pubic hair on her mound...eh..earth abides...right? btw..i would prefer hair on her cranium as well...(:(:(:
i think it's for sexual attraction,like peacocks,we impress mates with out hair-cause,you have to be healthy and have good genes to have good hair. I mainly believe this because hair has no other function-body hair does,but the hair on our head grows uncontrollably when it could do it's job as a protector from UV rays at a shorter length-so I say,sexual attraction it is.
Although hair does help in insulating the head area, the rest of the hair on your body is there to help regulate temperature it helps with sweating and it holds scent. So if you are sweaty and have hairy pits you would have smellier armpits than someone with no hair there. The plus side to the scent is the pheromones which turn a woman on are also trapped.