3 ms·
> moving to Northern climates with reduced sunlight resulted in decreased melanin (to ensure sufficient vitamin D) The Vitamin D hypothesis is just that, a hyp
by defen 11y ago
> moving to Northern climates with reduced sunlight resulted in decreased melanin (to ensure sufficient vitamin D)
The Vitamin D hypothesis is just that, a hypothesis, and probably not true. In the summer you produce enough after 10-15 minutes, and in the winter you produce none at all above a certain latitude. Furthermore, if it were a simple "loss of melanin" mutation, you would expect something similar to the favism mutation (G6PD deficiency) which protects against malaria - there are lots of ways to have a loss of function mutation, and you see a bunch with G6PD deficiency. Compare to SLC24A5 gene mutation, which reduces melanin production and accounts for a substantial fraction of paleness, and exists in 1 form that is fixed in most European populations. So paleness was probably selected for some other reason. FWIW there is also basically 1 blue eye mutation and 1 main blonde hair mutation.
> which allowed more ultraviolet damage thus increased mutations (blue eyes, red hair and so on).
I think you basically have this backwards. At the equator, in the evolutionary environment, you need dark skin to survive. Otherwise the sun will cook you. So there is very strong selection pressure to maintain that. Further from the equator, that selection pressure is relaxed. But it is not UV rays causing the mutations - rather, these random mutations happen (for whatever reason) and are not immediately culled by UV radiation, so if they provide some other advantage, it's possible they will win out.
Note: Everything I posted is also conjecture, I don't think anyone really knows why paleness mutations exist :)