Why did some hair evolve to be curly and some hair evolve to be straight? The answer is heating and air conditioning. (That is why there is a picture of the Lennox Man on the left.) Straight hair hangs close to your head and keeps you warm in the cold northern winters. It is like having a blanket for your head. Type 4 kinky-curly hair grows straight out from the head, often in an afro. In warm climates, the hair wicks sweat away from the head. As the sweat evaporates, it helps cool the head. Its nature's air conditioning system.