How do light and temperature affect the evolution of hair color?

If there was an ethnic race that evolved in a cold place with little light would it affect your hair color? I've been asking around and getting lots of different answers.


And what if that race evolved underwater, would it change their hair?How do light and temperature affect the evolution of hair color?
It entirely depends on the selective pressures, and furthermore, are we speaking modern civilization, hunter gatherers, pre-hunter gatherers?





It makes a huge difference. There is very little selective pressures I would imagine for hair color with current technologies and diets. There is not significant advantage or dissadvantage to any particular hair color.





At some point in time I imagine there were selective pressures. But let's think about cold areas with little light, what color fur do most animals in such places have? White or translucient fur is very common in such places. This likely plays into being able to better blend in with the background, but it also coincides with Gloger's rule, which states, than animals in humid locations near the equater tend to have darker pigments, and their counterparts in areas closer to the poles tend to have less pigment. This suggests that blonde hair would be advantageous in polar regions.





Here's another way to look at it. In areas of low light intensity, having darker skin was selected against because the skin pigments absorbed the light the human body needs to synth. vitamin D. This is not an issue with modern diets, but at one point it was. Now, dark hair will similarly absorb light allowing less to reach the scalp. Lighter hair absorbs less slight but reflects more, however, a decent amount of the reflected light is reflects at angles that still contact the scalp. So, there's another arguement for blonde hair.





One last argument which relates to the last one is that in areas of high light intensity, having pigments protects underlying tissues from damaging UV light. In areas where light isn't so intense, this isn't so much a problem. However, synthesizing the pigments requires energy, and before the times of hunter-gatherers life was tough and food scarce. And the most important thing in natural selection is making babies. So every little bit of energy that can be put into making more babies instead of making structures that aren't benificial is selected for. In other words, if a structure or chemical or what have you, grants no advantage in a particular environment, than it is inherently disadvantageous in the energy it wastes to create. Animals with the most free engergy to put towards making babies win.How do light and temperature affect the evolution of hair color?
Dark hair evolved at a colder place because it absorbs more of the lights energy and heats up more quickly. light hair evolved in hot places because it reflects the majority of the sun's energy, keeping body heat lower. If a race evolved underwater they would likely not have hair to increase hydrodynamics