Why move from black to white?
October 2, 2013 6:56 AM Subscribe
Why did the humans who came to Europe switch from dark to light skin pigmentation? Did they lose skin colour...?
There are two questions here - the second of which I only realised as I was trying to explain the first one.
1) If you imagine that (in a parallel universe) the cradle of humanity was somewhere in Sweden, I can understand the evolutionary logic for humans developing darker skins as they moved into areas that had harsher solar environments.
But, when a group of humans left Africa and moved across the Med and headed for Scandinavia, what was the benefit to losing the darker skin pigmentation? Is this 'just' a random quirk of genetics of the group that headed north, or is there some benefit to being pale? Is darker skin more biologically expensive to create or maintain? Does light skin allow better photo-reactions (vitamin D maybe?) than dark skin?
2) While writing that, I suddenly realised that I have no idea what colour skin humans had when we first spreading out to take over the planet. Is there any evidence as to what skin colour we had as early hominids?
There are two questions here - the second of which I only realised as I was trying to explain the first one.
1) If you imagine that (in a parallel universe) the cradle of humanity was somewhere in Sweden, I can understand the evolutionary logic for humans developing darker skins as they moved into areas that had harsher solar environments.
But, when a group of humans left Africa and moved across the Med and headed for Scandinavia, what was the benefit to losing the darker skin pigmentation? Is this 'just' a random quirk of genetics of the group that headed north, or is there some benefit to being pale? Is darker skin more biologically expensive to create or maintain? Does light skin allow better photo-reactions (vitamin D maybe?) than dark skin?
2) While writing that, I suddenly realised that I have no idea what colour skin humans had when we first spreading out to take over the planet. Is there any evidence as to what skin colour we had as early hominids?
but if you have dark skin but live in Scotland you're going to have issues.
Indeed. Rickets, caused a shortage of vitamin D, made a comeback amongst Asian immigrants to the UK about a decade ago. "The level of sunlight experienced in the UK over between late autumn and early Spring is not enough in itself to protect darker-skinned children from rickets."
posted by three blind mice at 7:11 AM on October 2, 2013 [1 favorite]
Indeed. Rickets, caused a shortage of vitamin D, made a comeback amongst Asian immigrants to the UK about a decade ago. "The level of sunlight experienced in the UK over between late autumn and early Spring is not enough in itself to protect darker-skinned children from rickets."
posted by three blind mice at 7:11 AM on October 2, 2013 [1 favorite]
As for 2)--and I'm assuming you believe in evolution, yes?--look at the skin coloring of our fellow primates, most of whom are pretty dark or gray, which is consistent with the answer to 1), given that fellow primates tend to live in sunny places, and we don't see monkeys swinging from pine trees in Lapland. I think that will give you a pretty good guess about what our early hominid forebears looked like in coloration.
posted by Admiral Haddock at 7:12 AM on October 2, 2013 [2 favorites]
posted by Admiral Haddock at 7:12 AM on October 2, 2013 [2 favorites]
What koolkat said, plus: if you eat huge amounts of meat, you can get enough Vitamin D directly from the meat. So many peoples who live in dark places but hunt a lot kept their darker skin. Light skin means you're from an extreme latitude, and your ancestors subsisted on plants. This combination of factors only really happened in northern Europe.
posted by miyabo at 7:14 AM on October 2, 2013 [5 favorites]
posted by miyabo at 7:14 AM on October 2, 2013 [5 favorites]
This map shows native human skin color variation. Generally, people exposed to a lot of sun are dark in coloration to protect the skin from the sun. People exposed to little sun are light in coloration to get more vitamin D.
So, skin coloration is usually a function of how close to the equator a population is (more sun) and how much cover there is (people who live in forests are lighter).
However, diet is also a factor. Inuit get vitamin D from the food they eat, so even though they are exposed to very little sun, they are not as white as Caucasians. But Caucasians evolved eating wheat, which has almost no vitamin D. So, they evolved very white skin to compensate, at a cost of sunburn, skin cancer and freckles.
posted by musofire at 7:16 AM on October 2, 2013
So, skin coloration is usually a function of how close to the equator a population is (more sun) and how much cover there is (people who live in forests are lighter).
However, diet is also a factor. Inuit get vitamin D from the food they eat, so even though they are exposed to very little sun, they are not as white as Caucasians. But Caucasians evolved eating wheat, which has almost no vitamin D. So, they evolved very white skin to compensate, at a cost of sunburn, skin cancer and freckles.
posted by musofire at 7:16 AM on October 2, 2013
Evolution does not necessarily mean that light skin was somehow made to be "better" for colder climates. It just means that specifically in colder climates, if some people happened to have had a mutation that caused their skin to have less pigment, then in northern climates it would have been just as possible for them to survive and reproduce as it would for darker skinned people. The darker skin was not an advantage in that environment, so it was possible for a fluke to proliferate.
Evolution just means that if something doesn't kill you or your babies before reproducing, your genes can replicate over the population.
I appreciate the above answers giving a more complex picture involving diet etc. -- and as I am not a scientist my answer is not engaging with that fuller picture. I am just trying to point out to the rest of us non-scientists that evolution often works not by "finding" the best solution, but by not eliminating an arbitrary one.
posted by third rail at 7:28 AM on October 2, 2013 [5 favorites]
Evolution just means that if something doesn't kill you or your babies before reproducing, your genes can replicate over the population.
I appreciate the above answers giving a more complex picture involving diet etc. -- and as I am not a scientist my answer is not engaging with that fuller picture. I am just trying to point out to the rest of us non-scientists that evolution often works not by "finding" the best solution, but by not eliminating an arbitrary one.
posted by third rail at 7:28 AM on October 2, 2013 [5 favorites]
Oh, I read somewhere a hypothesis that the reason for unusually blonde people in northern Europe (compared to people in northern China or America) is that the Gulf Stream allows us to grow wheat at northern latitudes, giving us a vitamin-D deficient diet. Native Americans from similar latitudes didn't have agriculture at all, and Chinese people were eating rice, which has vitamin D.
posted by emilyw at 7:30 AM on October 2, 2013 [1 favorite]
posted by emilyw at 7:30 AM on October 2, 2013 [1 favorite]
Response by poster: All - I 'believe in' and understand evolution as a concept, but for an entire region of a species to show the same trait, it's presumably more than a random mutation that merely didn't kill the population...?
Admiral Haddock - except that our closest neighbour, the chimpanzee, has quite a pale face and hands. And, since I've never seen a shaved chimp, I have no idea what colour the rest of it's skin is.
musofire - that map is fascinating, both for the obvious latitudinal banding of skin colour and the places where skin colour completely ignores the latitude.
EmilyW - Thank you. *goes off to try that reading thing...*
posted by sodium lights the horizon at 7:44 AM on October 2, 2013
Admiral Haddock - except that our closest neighbour, the chimpanzee, has quite a pale face and hands. And, since I've never seen a shaved chimp, I have no idea what colour the rest of it's skin is.
musofire - that map is fascinating, both for the obvious latitudinal banding of skin colour and the places where skin colour completely ignores the latitude.
EmilyW - Thank you. *goes off to try that reading thing...*
posted by sodium lights the horizon at 7:44 AM on October 2, 2013
given that fellow primates tend to live in sunny places,
The ones that don't? Check their skin color. Not just humans who made this adaptation.
posted by Slap*Happy at 8:19 AM on October 2, 2013 [3 favorites]
The ones that don't? Check their skin color. Not just humans who made this adaptation.
posted by Slap*Happy at 8:19 AM on October 2, 2013 [3 favorites]
Don't mistakenly think this is binary: African dark/Swedish light
The people who brought grain cultivation and the attendant culture to Europe, and whose descendants are now what we call "westerners" were probably coming from the area around the Black Sea/Turkey. These Indo-Europeans were probably lighter in skin tone than their distant African ancestors, and darker in skin tone than their distant Nordic descendants.
posted by General Tonic at 8:19 AM on October 2, 2013 [2 favorites]
The people who brought grain cultivation and the attendant culture to Europe, and whose descendants are now what we call "westerners" were probably coming from the area around the Black Sea/Turkey. These Indo-Europeans were probably lighter in skin tone than their distant African ancestors, and darker in skin tone than their distant Nordic descendants.
posted by General Tonic at 8:19 AM on October 2, 2013 [2 favorites]
except that our closest neighbour, the chimpanzee, has quite a pale face and hands. And, since I've never seen a shaved chimp, I have no idea what colour the rest of it's skin is.
There are a fair number of hairless chimpanzees (via alopecia) that live in zoos. Their skin is fairly dark.
posted by jedicus at 9:15 AM on October 2, 2013 [1 favorite]
There are a fair number of hairless chimpanzees (via alopecia) that live in zoos. Their skin is fairly dark.
posted by jedicus at 9:15 AM on October 2, 2013 [1 favorite]
All - I 'believe in' and understand evolution as a concept, but for an entire region of a species to show the same trait, it's presumably more than a random mutation that merely didn't kill the population...?
Remember that this is all taking place over a veeeery long time frame. It's not just that the mutation didn't kill the population, but that the mutation had the benefit of allowing those with the mutation to live longer (presumably by avoiding rickets, which can cause a host of health problems)--long enough to reproduce--while those with darker skin would have died in greater numbers before they lived to be able to reproduce. With each successive generation, there would have been a greater population of those with lighter skin, better able to synthesize vitamin D from sunlight.
posted by PhoBWanKenobi at 10:53 AM on October 2, 2013 [1 favorite]
Remember that this is all taking place over a veeeery long time frame. It's not just that the mutation didn't kill the population, but that the mutation had the benefit of allowing those with the mutation to live longer (presumably by avoiding rickets, which can cause a host of health problems)--long enough to reproduce--while those with darker skin would have died in greater numbers before they lived to be able to reproduce. With each successive generation, there would have been a greater population of those with lighter skin, better able to synthesize vitamin D from sunlight.
posted by PhoBWanKenobi at 10:53 AM on October 2, 2013 [1 favorite]
Also we're talking about humans, not bacteria. We know that discrimination based on skin color has been a feature of many, many societies around the world. It's plausible that at some point, people either killed or refused to mate with people based on skin color, hastening the selection towards light skin. (So -- first evolution produces a subset of people there with light skin, they decide for whatever reason not to mate with / allow dark skin people in their society [for whatever reason humans repeatedly do this], and thus light skin people reproduce much more successfully).
Since this basically happened all before recorded history, we can't really know the influence of society or culture, but you can see these sorts of effects in recorded history (look how the arrival of the Europeans affected skin color / race in South America) so it seems plausible they happened before too. (I have no idea whether theres any way to show this either way)
posted by wildcrdj at 11:01 AM on October 2, 2013 [1 favorite]
Since this basically happened all before recorded history, we can't really know the influence of society or culture, but you can see these sorts of effects in recorded history (look how the arrival of the Europeans affected skin color / race in South America) so it seems plausible they happened before too. (I have no idea whether theres any way to show this either way)
posted by wildcrdj at 11:01 AM on October 2, 2013 [1 favorite]
It is quite likely that "natural"/darwinian/genetic selection on the basis of Vitamin D production was a factor, but I wouldn't dismiss "cultural" selection.
I would also note that the distinction I've drawn between natural and cultural factors is ridiculously artifical. Culture is natural, and even within that artificial distinction cultural and genetic factors are going to influence one another across generations, including people inventing genetic justifications for their cultural biasis.
posted by Good Brain at 11:54 AM on October 2, 2013 [1 favorite]
I would also note that the distinction I've drawn between natural and cultural factors is ridiculously artifical. Culture is natural, and even within that artificial distinction cultural and genetic factors are going to influence one another across generations, including people inventing genetic justifications for their cultural biasis.
posted by Good Brain at 11:54 AM on October 2, 2013 [1 favorite]
This thread is closed to new comments.
posted by koolkat at 7:00 AM on October 2, 2013 [11 favorites]