system
Given the following post, respond as if you're commenting on Reddit:
human
Why did Asians evolve? [LI5]

From what I understand, human skin became lighter as they moved north out of Africa due to lower sunlight, in order to get more vitamin D.  This would explain why there are whites and blacks, but why did Asians evolve?  Are my initial premises about whites and blacks wrong?
gpt
Asians tend to live in coastal regions.  China's interior is practically empty compared to the coasts.  Fish provide a lot of vitamin D, so the skin doesn't need to get as pale.  That's why, for example, Spaniards and Italians tend to be pretty swarthy.