[In the answer to this question](http://worldbuilding.stackexchange.com/questions/27958/hair-based-architecture#28068), it is said that that is needed to be done to make the solution 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 (let's say 2 cm a week). I only have 2 constraints:  

 1. They must have evolved this in, around or near jungles (for story reasons).
 2. I would prefer explanations other than sexual selection; that is an obvious answer that is over used by worldbuilders.