If too much exposure to the sun causes cancer, how are there still any fair-skinned people on earth? For the vast majority of human history, we didn’t have sunblock. Shouldn’t we gingers be extinct by now?

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If too much exposure to the sun causes cancer, how are there still any fair-skinned people on earth? For the vast majority of human history, we didn’t have sunblock. Shouldn’t we gingers be extinct by now?

In: Biology

The further away from the equator the lighter your skin tone. It allows you to absorb more vitamin D (if I remember rightly) because there’s less sun in those areas so skin cancer wasn’t much of a
Problem until we started shifting ourselves round the globe… or something like that.

Fair skinned people produce more vitamin D then dark skinned people when exposed to the same levels of sunlight. So the same way that fair skinned people have a higher risk of cancer by living in the low latitudes dark skinned people have had a traditionally higher risk of vitamin D deficiency by living in the high latitudes.

Cancer usually occurs in older people, and people would have had children at much younger ages historically. It is highly unlikely that a person would develop fatal skin cancer from sun exposure before they already had kids. So it wouldn’t prevent them from procreating and passing their genes along. I would guess that historically most people didn’t live long enough to get cancer any ways, they would probably die from other diseases much sooner.

Take a look at this map

http://www.thewhirlingwind.com/wp-content/uploads/2013/07/Map_of_Indigenous_Skin_Colors.png

This is a map of the world colored based on the average skin tone of the people native to that area. As you can see, how dark your skin is is more or less just a function of how far away you are from the equator. Fair skinned people, for the majority of human history, lived in areas that didn’t get much sunlight. The lighter skin was actually an advantage because it’s better at absorbing vitamin D, which would have been in shorter supply. Fair skinned people didn’t venture out of those areas in large numbers until relatively recently. So there wasn’t a lot of time for natural selection to take over and weed people out. And since we spend more of our time in doors and have access to things like sunblock, the evolutionary pressure isn’t as strong as it would have been tens of thousands of years ago.

There is evidence that our ancestors started to wear clothes as far back as 100,000 to 500,000 years ago so it might predate the modern human species. The evolution to lighter skin is likely in the last 50000 years so it did not happen when we did not have a way to protect us from the sun. Clothes are a very good sunblock.

Modern human species is around 200,000 years old so for the majority of humans the skin for all was dark.

The skin color depends on evolutionary skin exposure. if you get to little UV light in your skin you produce too little Vitamine D.

Too much UV and it will break down Folate that is very important during pregnancy. So the skin color evolve towards a point where you get enough of both

For a human with dark skin, the children tend to be paler than adult likely as a way to get more Vitamine D when you grow and more Folate when you are pregnant.

Rickets is what you can get wit to low Vitamine D levels. You hade a lot of it in UK primary during the industrial revolution when in some periods 80% of children in London had it when so much of the sunlight was blocked by smog and fog. It can today be solved by supplementing Vitamine D.