Human's were black before they left Africa. After thousands of years of living in different climates and eating different foods - their skin complexions became variations of brown and they started to look physically different. The genetic paths of skin change and physical characteristics followed a few different paths in Asia and Europe.
For nearly 2 Million years everyone on Earth was a dark skinned African. Our ignorance used to makes us believe that soon after leaving Africa humans started to change because of V D absorption. We now know that that isn't true. Human's did not start to change 40k years ago for 2 reasons - 1) it doesn't happen over night - it happen because of sex and entire populations don't change that quickly... especially when we were all black africans 2) Researchers show that it could have been as recently as 6000 years ago that we were prompted to make skin color and other physical changes - and that was mainly due to diet and how we produced food.
It takes at least 100+ generations (not a made up fact) for populations to even make the changes we are talking about when mating amongst themselves.
Natural section is the reason we maintained dark skin and 'African' features. The SC what would make the changes - and the stratum corneum has had the greatest change right after we became 'homo sapiens' and modern humans ---- supposedly due to loss of hair (idk if the loss of hair is the reason, but that's what
they say). Natural selection favors mutations that protect the protective functions of the skin. NTM, all the reproductive issues that arise when a species gets away from it's original form. Natural selection protects against that. Plus there are links between melatonin and reproduction - scientist say that, but i guess we only think that the Afrocentric people are the only ones that make that claim. Plus, regardless of where you live on Earth, lighter skin is a recessive trait ..... more than likely will balance out in the next 1k years.
in ancient times there were groups on our planet that have completely different cultures and development than their African ancestors. That doesn't mean that the link between them and the people who settled their lands is null and void. To say that is to make some shyt up about how populations completely changed withing 2K years and that's just not possible. The equivalent is Africans in America. The person who's people came here in the 1700's more than likely isn't gonna randomly look like a African in 2100. But I'm sure you will be able to call that person African American. This is the same as in Antiquity except for they were EVEN less mixed and disconnected. There is a reason why in some of these asian lands, ancient historians confuse them with Africans. Only a lil over 6K years ago did we make these changes...... but due to the way people look today - people use modern examples to DE-africanize ancient groups and cultures.
http://www.ncbi.nlm.nih.gov/pubmed/19439728
http://en.wikipedia.org/wiki/Stratum_corneum