[In the answer to this question](http://worldbuilding.stackexchange.com/questions/27958/hair-based-architecture#28068) He says all that is needed to be done to make it feasible is to increase the growth rate of human hair. But the problem is that I cannot think of any evolutionary explanation for hair growth to be that quick. What evolutionary history would support quicker hair growth(lets say 2 cm a week). I only have 2 constraints;  

  *  one, they must have evolved this in, around or near jungles( for story reasons)

  *  Two, I would prefer explanations other than sexual selection, that is an obvious answer that is over used by worldbuilders.