darker skinned people are generally hunter gathers whilst light skinned people are farmers. the light skin owing to loss of melanin and trading its protection inorder to get more vitamins from the sun as these agriculture based diets are no longer providing the vitamins humans had previously evolved to depend upon that are gained from hunting. and since succesful agriculture outcomes depends more on cognative skills such as forward planning, and larger more complex social groups, human groups that focused on agriculture selected less for physical traits of hunter gatherers and more for cognative traits, for which the increased provision of calories provided from agriculture allowed for larger brains with its greater energy requirements.
in america, the darker skinned people are from west africa, in this region food is naturally abundant without the need for agriculture, and the stable weather also means cold weather clothing or structures has never been a requirement for survival selection. the level of cognative ability for successful survival in this region is limited to the level of having advantage over the animal life which the west african would be competing against for food.
