Scanning the circumference of the earth taking notice of human hair variation; we can count one major dichotomy in human hair shape: that of loose hair that hangs down towards the earth and that of hair that builds upward spherically.

     In Africa where their exists extraordinarily heavy air; enough to resist moving in a stream-like fashion we find hair that mimics a contained, non-streaming and cloud-like motion.

  
     In the rest of the world where the air isn't heavy enough to resist streaming motion; hair evolved in order to mimic this streaming motion.

Lighter air: non-contained streaming motion

Heavy air: non-streaming contained motion

                                                                            TEST:

Can you tell the difference???????
One picture is in India where the hair mimics a streaming movement and the other picture is in Africa where the air is heavy enough that their is no streaming movement.