The main factor correlated with human populations losing skin pigmentation is the distance from the equator. Populations living closer to the equator have higher levels of melanin in their skin to protect against the sun's harmful UV rays, while populations living farther from the equator have lower levels of melanin due to reduced sun exposure. This adaptation is known as the "latitude gradient in human skin coloration." Other factors such as dietary changes, genetic mutations, and interbreeding with other populations can also play a role in the loss of skin pigmentation.
