Micro Life Zone
Asked by millie to Brad, Chris, Herbert on 23 May 2012.
Keywords: acid, colour, evolution, folic, skin, vitamind
This is an great question, where does your interest in this come from?
Vitamin D is an essential molecule that we get from our diet, but it requires metabolism, or conversion to an active form, by sunlight. Humans originally evolved in Africa, where sunlight is in abundance and therefore vitamin D is relatively easy to make. When humans moved out of Africa and into Europe, where there is less sunlight, vitamin D becmae harder to make and the belief among evolutionary biologists is that Europeans skin evolved to become lighter in order to make the sunlight-vitamin D conversion more efficient. This is called “selective pressure” of being in a different environment, and is a good (if unproven) example of how evolution works.
I am less clear about the role of folic acid, but I believe that sunlight reduces the levels of folic acid in the skin, and darker skin helps protect against this. Since humans evolved in Africa and presumably had darker skin at first, folic acid retention would have been a negative selection pressure *against* lighter skin (ie it favours dark skin), but moving away from sunlight (into Europe) would remove this negative selection pressure and allow skin to become lighter to provide the vitamin D advantage.
Chris has already answered your question fairly well for vitamin D, but there is also a competing theory that there is enough vitamin D available to be healthy. Although the synthesis is less with reduced sunlight, it is supplemented with food. When farming occured, there was a diet change – reduced eating of game meat and some plants. This means the body needs to synthesise more vitamin D.
On the other side, with folic acid (Vitamin B9), Chris is right that sunlight (UV) breaks them down. Folic acid/folate is important in pregnancy so there would be an advantage to protect folic acid. As farming increased the availability of leafy vegetables (which contains folic acid), the body could determine that folic acid is no longer a problem. As vitamin D levels need to be increased in the body, this leads to lighter skin colour.
This area is currently explored in genetics, and as this is not my field, I can not say which theory is correct, but perhaps it is something you can explore.
By BRIDGE8 under license from Mangorolla CIC 2022