Question: Why do some of us have different colour skin, or is that not science ?

Susan Cartwright answered on 23 Jun 2015:

It is science, although in dealing with it one has to be sensitive to cultural issues.

Essentially, the darkness of your skin tone is set by the amount of melanin your skin cells produce. Melanin is the dark pigment that affects both skin and hair colour. So Europeans produce very little melanin (though exposure to sunlight stimulates the production of more, which is why we tan), whereas sub-Saharan Africans produce a lot. The amount of melanin you produce is determined by genetics; several genes are involved, which is why there is such a range of skin tones (and why two parents of different skin colours tend to have babies with intermediate colour). Redheads produce a different version of melanin, called pheomelanin, which non-redheads convert into the usual form (eumelanin) – the gene that makes the enzyme that does this is not working properly in redheads. This is why redheads typically have very pale skin and do not tan easily.

That’s *how* we wind up with different skin colours. *Why* is probably down mostly to sunlight. Too much sunlight is bad for you, as it increases the risk of skin cancer. Too little is also bad for you: you don’t make enough vitamin D, and may end up with bones that don’t grow properly. The amount of sunlight depends on where you live – near the equator, you get lots: near the poles, much less. So people who settled in northern latitudes tended to develop light skin to maximise vitamin D, whereas those who lived in the tropics wound up with dark skin to block UV and reduce skin cancer.