system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Out of Africa - How does that explain the diverse cultures, body types, eyes, and skin colors present today?
gpt
Large amounts of melanin help prevent UV damage to the skin. Wearing more clothes and/or moving to colder/darker areas means loss of melanin makes little difference. Skin gets lighter.

People in colder areas have higher body fat content and fattier diets, in order to insulate themselves against the cold.

Babies lose the lactase protein as they grow older, causing them to become lactose intolerant. People who domesticated cattle were more likely to retain the lactase gene into adulthood.


In all of these situations, you have to take into account that the people that are better attuned to the environment are more likely to have children that survive into adulthood and make up the next generation.

Other factors play a part as well. A few survivors of a plague may repopulate, causing the entire population to overwhelmingly share from a smaller pool of different genes. Viking raids may in part explain why Scandinavian countries have a high percentage of blond(e)s.


That's only talking about features we can observe. As far as actual genetic comparisons, 2/3 of human history has been spent in Africa. There are groups in Africa that are genetically closer to everyone outside Africa than they are to other groups on the continent.