Skin color, it turns out, is little more than adaptation in action

[Viva_La_Revolution]

So here’s a thought: How did different skin colors evolve? Evolutionary biologist Nina Jablonski wrote the most widely accepted theory in 2000, saying that it comes down to a practical combination of three things: skin, ultraviolet light and vitamins.

The story begins in Africa, about two million years ago, when early members of the genus Homo began moving from the cool cover of forests onto sunnier open plains to find food. These early humans were densely covered in hair, which increased their body temperatures and made them slower hunters.

Thanks to genetic variation, some were born with less hair. Since those less-hairy hominids had a survival advantage, natural selection kicked in over thousands of generations, and body hair gave way to bare skin populated by sweat glands. These became the body’s escape route for heat and created a further evolutionary advantage for these humans by making them more effective hunters and therefore, more attractive mates.

http://scienceline.org/2012/02/the-skin-were-in/

[Ecumenist]

1. No kiddin', I've always known that. This is EXACTLY why racism is so STUPID and pointless.

If my descendents moved to somewhere like Sweden and stayed there for the next half million years, their skin would eventually lighten up due to being selected for more effective vitamin D absorption and certain aspects of their physical appearance, ie, hair, shape of the nose etc would change in relation to their climate.

[MarkCharles]

4. Yes, but it wouldn't have to take that long...

Most estimates of the change in skin pigmentation as an adaptive advantage in evolution say the change happened within the last 50,000 years, at most. Remember, children matured earlier, lived very short lives, and were producing children, a next generation, within 13-20 years. Every hundred years back then could customarily produce 5 or 6 or 7 human generations, whereas nowadays each century usually only produces 3 to at most 5.

[Ron Obvious]

9. Indeed, blue eyes are even more recent

I think recent studies have shown that all of us blue-eyed people have a single common ancestor a mere 10,000 years ago. Blue eyes are blue because of low levels of melanin and absorb light at different wavelengths which gives a survival advantage in more northern latitudes.

There's only 150 million of us in the world today and our numbers are shrinking because it's a recessive gene, but to the best of my knowledge nobody is taking up a collection yet.

[MarkCharles]

10. I love you blue-eyed gals and guys!!!

Yes, recessive, but I'm not sure that there's an advantage for survival, sadly, now that we have electric lights.

So were there only two parents who produced the first blue eyed child? Then how does that recessive gene go on to be replicated in successive generations without brother and sister, first and second and third cousins mating?


I bet there were numerous simultaneous offspring with this genetic variant in some villages in Northern Europe, about 10,000 years ago. Several of them mated with each other, etc.

[Ron Obvious]

11. I suspect you're right about lack of advantage these days...

But remember that evolution occurs in populations, not individuals, so once a particular gene is present in a population it will out if there's a survival advantage. I think the recessive nature is along the lines of 1 out of 4 children having blue eyes and 3 out of 4 having brown eyes if there's one parent of each eye colour. So blue eyes will pop up occasionally as long as the (single) gene for them is in the gene pool somewhere. I was able to assure a brown-eyed friend that he was probably still the father of his blue-eyed child despite the mother also having brown eyes.

Of course it can't neatly add up to four out four like that. Years ago, I had teacher with one brown eye and blue eye. Gave me the creeps, actually; it's an odd look.

[MarkCharles]

12. Oh yes, I forgot, but any recessive gene has to...

be present in TWO parents.

So it is likely that this strange mutation occurred more than one time in one contemporary generation.

I bet it is likely that it occurred many many times in many simultaneous contemporary generations in many places in Europe. Strangely, it seems to have never occurred in Africa or Asia, I gather.

I'm not sure how blue eyes ever had a survival advantage in Europe, where many longer colder dark nights were around each winter season. Do blue eyes give their owner a better night vision? A better protection against cold? A better ability to see small prey on a field of white snow? I'm not sure how eye color changes the quality of vision. Can you explain more?

[Ron Obvious]

14. Well, I don't know much more about it than I said

I'm afraid I'm not much of an expert in these things and I didn't even know recessive genes had to be present in both parents. I know that in cases of haemophilia and genetic diseases like that it's true, hence the bans on marrying too close to the bloodline, but I don't know if it's true in all cases. Up until I read the Wiki article mentioned below, I thought there was a just single gene for blue eyes. Whether the mutation could have occurred elsewhere and not have provided survival advantage there, I really couldn't say. I don't think we see it animals much, except maybe for Huskies and Siamese cats.

As for survival advantages, I can confirm that I have far better night vision than my brown-eyed wife, although I'm not 100% sure of the mechanism or if that's typical. Considering the long, dark winter nights in the north, I imagine better night vision would be a survival advantage. If for no better reason than that it would help the mating process if you can find someone to mate with, which activity would also help keep you warmer on those cold nights, I suppose, and make one less likely to be found frozen to death the next morning and tossed out on the rubbish pile after breakfast, at which point one is usually done passing on their genes.

[Jim__]

13. "The genetics of eye color are so complex that almost any parent-child combination of eye colors ...

... can occur."

According to the article in wikipedia on eye color, your assurance to your friend was correct. An excerpt:

Eye color is a polygenic phenotypic character and is determined by two distinct factors: the pigmentation of the eye's iris[1][2] and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.[3]

In humans, the pigmentation of the iris varies from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma.[4] The appearance of blue, green, and hazel eyes results from the Rayleigh scattering of light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky. Neither blue nor green pigments are ever present in the human iris or ocular fluid.[3][5] Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes.

The brightly colored eyes of many bird species result from the presence of other pigments, such as pteridines, purines, and carotenoids.[6] Humans and other animals have many phenotypic variations in eye color.[7] The genetics of eye color are complicated, and color is determined by multiple genes. Some of the eye-color genes include EYCL1 (a green/blue eye-color gene located on chromosome 19), EYCL2 (a brown eye-color gene) and EYCL3 (a brown/blue eye-color gene located on chromosome 15). The once-held view that blue eye color is a simple recessive trait has been shown to be incorrect. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.[8][9] OCA2 gene polymorphism, close to proximal 5′ regulatory region, explains most human eye-color variation.[10]

[Ron Obvious]

15. Interesting article!

I'd share it with my friend but I think he's no longer concerned with the matter.

[Warpy]

2. Hair slows you down?

Tell that to a cheetah. Or a kangaroo. What a lack of hair might do is allow one to cool down easier after a burst of activity but even that is doubtful.

Chances are we went bare because of fashion. Barer mates were chosen over really hairy ones, much the way starveling women are given the edge today.

As for skin color being adaptation, chances are that's also a result of people leaving Africa interbreeding with Neanderthals, Denisovians and other earlier humans. We know, for instance, that Neanderthals were fair skinned with reddish hair.

[MarkCharles]

3. Cheeta's runs are episodic, only happening a..

few times a day. cheetas also pant ferociously between the runs, and seek cool areas to rest and recover and to hide from the next potential prey. Of course, cheetas are anatomically built for much faster running than humans are capable of doing. So hunting hominids spent hours in the hot plains of Africa in search of food.

But more important here, I think the loss of body hair, and the admixture of homo sapiens genes from mating with Neanderthals and Denisovans were events separated by some tens of thousands of years along the last couple hundred thousand years of our history.

[Viva_La_Revolution]

5. Warpy, I think you're off a little..

fashions don't last long enough to force evolution. and some of us still prefer our men on the hairier side

Here's a link to the same info as in the OP, but with more detail. Skin color is most definitely a result of the ability or necessity of sunlight for us to process vit. D and folic acids.
http://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_04.html

[Warpy]

7. It's no sillier than the idea that hair slows you down.

C'mon now, you know that to be true.

[Viva_La_Revolution]

8. oh yeah, I agree there.

[Ichingcarpenter]

17. Long body hair does slow you down.

We have the same amount of hair as a chimp except
ours are very fine and short. Chimps over heat because of this. We can run down a gazelle, bushman do this all the time. They track the animal for miles until it is exhausted in the heat of the day. Perspiration can evaporate more easily because of our fine body hairs.

Think about that... we have the same amount of body hair as a chimp.

[muriel_volestrangler]

6. It's for 'persistence hunting'

http://en.wikipedia.org/wiki/Persistence_hunting

There's a very good sequence in David Attenborough's "Life of Mammals" (referred to in that article, but I can't find it on YouTube, apart from one blocked by the BBC on copyright grounds), where they filmed a bushman in the Kalahari running down a kudu - he's not faster than it at first, but it has to stop more and more often to cool down when it finds shade. Eventually, it just cannot run any more. The ability of the man to be able to jog and cool down at the same time is vital.

Also, for skin colour being from interbreeding, (a) you'd need to ask why would the Neanderthals and Denisovians had lighter skin - the same ideas of vitamin D production would be relevant (b) you also need to consider the darker skins of groups nearer the equator among populations that migrated into new areas like the Americas or Australia. The map of skin tone clearly shows that when there's no question of differences in Neanderthal or Denisovian interbreeding, darker skins reappear near the equator.

[Thor_MN]

16. Ah, the good old days.

What I wouldn't give to hear "My dad is more hairless than your dad!!"

[sakabatou]

18. I learned this years ago

Why are they printing it now?