SKIN COLOUR
 
Oval: Folic acid exists in skin Oval: UV rays produce vitamin D3
Oval: UV rays destroy folic acid
Oval: Too much melanin stops D3 production
Oval: Increased melanin screens out most UV rays
Oval: Reduction of melanin in the north allows D3 production
Oval: Result: folic acid is protected.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At the equator, melanin production is heavy because the people need to protect their folic acid levels.  Enough UV rays get through the skin, however, to allow Vitamin D3 production.

 

If these people move north where there are less UV rays in the air, things change.  The skin must lighten to allow UV rays in for the production of vitamin D3.  The UV rays are weaker and the folic acid in the skin is not threatened. 

 

Since humans originate in Africa, black skin lightened over time as the humans migrated northwards.