Looking at the map of the distribution of blue eyes in Europe made me wonder: why do Europeans have blue eyes? Were they found in other parts of the world before European expansion and inter-marrying?
https://unsafeharbour.files.wordpress.com/2012/02/maps-europelighteyes.jpg?w=584
The genetic allele that produces blue eyes appears to have originated about 6,000 to 10,000 years ago near the Black Sea.Blue eyes may appear sporadically in other populations due to new mutations, but in most people with blue eyes the trait is due to this allele.
The direct selective benefits of blue eyes are obscure (unlike light skin, for which several possible selective benefits have been proposed, especially the production of vitamin D in areas with restricted sunlight). As the article suggests, one hypothesis is that the trait spread through sexual selection since it was considered attractive.
There is an interesting overlap in the timing and spread of the lactose tolerance gene mutation with the blue eye mutation. Most likely that’s either coincidence or connected a step farther back through the spread of lighter-skinned peoples. Makes me wonder if anybody has looked into a correlation between the two mutations.
Getting laid? that’s the only reason the mutation has survived?
So why hasn’t it spread more widely?
Just post to expound on Colibri’s post:
Bito, L. Z., A. Matheny, K. J. Cruickshanks, D. M. Nondahl, and O. B. Carino. 1997. Eye color changes past early childhood: the Louisville Twin Study. Archives of Ophthalmology 115: 659-663.
Boas, H. M. 1918. Inheritance of eye color in man. American Journal of Physical Anthropology 2: 15-20.
Brues, A. M. 1975. Rethinking human pigmentation. American Journal of Physical Anthropology 43: 387-391.
Davenport, G. C., and C. B. Davenport. 1907. Heredity of eye color in man. Science 26: 589-592.
Holmes, S. J., and H. M. Loomis. 1909. The heredity of eye color and hair color in man. Biological Bulletin 18: 50Ð65.
Hurst, C. C. 1908. On the inheritance of eye-colour in man. Proceedings of the Royal Society of London B 80: 85-96.
Liu, F., et al. (20 co-authors). 2010. Digital quantification of human eye color highlights genetic association of three new loci. PLOS Genetics 6: e1000934.
Mackey, D. A., C. H. Wilkinson, L. S. Kearns, and A. W. Hewitt. 2011. Classification of iris colour: review and refinement of a classification schema. Clinical and Experimental Ophthalmology 39: 462-471.
Matheny, A. P., and A. B. Dolan. 1975. Changes in eye color during early childhood: sex and genetic differences. Annals of Human Biology 2: 191-196.
Pospiech, E., J. Draus-Barini, T. Kupiec, A. Wojas-Pelc, and W. Branicki. 2011. Gene-gene interactions contribute to eye colour variation in humans. Journal of Human Genetics 56: 447-455.
Sturm, R. A., and M. Larsson. 2009. Genetics of human iris colour and patterns. Pigment Cells and Melanoma Research 22: 544-562.
If it did only originate 6-10 thousand years ago, I’d say it’s spread pretty fast, especially given that it’s a recessive allele.
That would be absolutely fascinating! waves wand Dopers, get to it!!
Nature knew in advance that humans would need pilots.
Not sure how true it is but I’ve read that people with blue eyes can hold their alcohol better and feel less pain.
http://dailycaller.com/2014/06/10/how-pain-tolerant-are-you-your-eye-color-may-hold-the-answer/
Could be true I suppose, I’ve also read that redheads were more more sensitive to certain types of pain but had a higher pain threshold for pain caused by an electrical current.
Blue and green eye are reasonably common all the way to India, so I suspect that it has to be multiple mutations. East and South of the Sub continent ], they are almost unheard of.
Previous to the mutation, do we know if newborns still had blue eyes and they darkened over time?
Since India is known to have had influx from the area where these genes originated, what with the indo-european language group and everything, why would you need to posit multiple mutations?
[WAG] Some changes come about because they come along for the ride, so to speak, with other useful changes. Read Stephen J. Gould’s essay, The Panda’s Thumb, the title essay in the book of the same name. The point made in the essay is that, while the panda’s forethumb is useful for stripping bark from bamboo, what is interesting is that the panda has a useless rear thumb that evolved along with it. In a similar way, it is entirely possible that blue eyes just happened as a result of some general loss of pigment mutations. After all, skin color is probably under control of a number of genes. One of my grandfathers was a blue-eyed pale blond. I am blue-eyed, but rather dark skin. Just the way genetics work I guess.
Just for the record, the panda’s thumbs are not hand bones, but modified wrist/ankle bones.
Well, if light skin is useful (and it is) in absorbing more sunlight to make vitamin D, lactose tolerance is also useful for getting vitamin D from dairy products, and getting calcium from dairy products in the winter, when many of the sources that people in warmer climates depend on are not available. Since D is necessary for processing calcium, getting them together is helpful.
I don’t want to sound like I don’t advocate breast-feeding, because I do, and I breast-fed my son, but dark-skinned babies, particularly African-American babies who are breast-fed, and are also winter babies, sometimes need vitamin D supplements in the US, because they don’t absorb enough sunlight, and breastmilk doesn’t have vitamin D. Babies are born with a reserve of D, but it usually is exhausted before they are ready to eat solid foods, if they have very little light exposure.
This post reports study findings that seem to suggest that among groups in South and south-central Asia that include people with light-colored eyes, one group does have some European genes from historical antiquity (i.e., the “Alexander’s army effect” and similar population contacts).
The others were apparently found to have no European genetic heritage. That finding, if true, sounds to me as though it would rule out European ancestry for at least some of the light-eyed South Asians. So maybe multiple mutations is the explanation, or part of it?
There are definitely (once) isolated lighted eyed populations that have separate origins. But AK84 posited multiple mutations as an explanation of the reasonably common occurance of light eyes from Western European all the way to the Indian sub-continent.
Bumping an old thread because of the recent news articles that Cheddar Man in Britain had blue eyes and dark skin, with similar speculation as to why blue eyes evolved:
Britain’s Dark-Skinned, Blue-Eyed Ancestor Explained
How and when Britons developed lighter skin over time is unclear.
“We think it’s because light skin allows for more UV radiation, which helps break down vitamin D,” says Vilar. In more temperate regions, where ancient humans were less exposed to sunlight, they would have needed to absorb more radiation to break down the essential vitamin needed for healthy bones.
“In my view, that’s the most robust theory for skin pigmentation,” says Thomas. **“But it doesn’t explain eye pigmentation. There are other processes that go on. It could be sexual selection. **It could even be something else we don’t yet understand.”
There is not just one “lactose tolerance” gene - there are some dark-skinned, dark-eyed African groups that have a lactose tolerance gene (such as the Maasai) that apparently arose separately from the European one. Not surprisingly, lactose tolerance in Africa overlaps with keeping cattle.
Of course, in Africa getting sufficient sunlight for vitamin D production is pretty easy to do so co-evolving light skin was unnecessary. In Europe, being able to utilize vitamin D in the diet alongside evolving lighter skin might have had some advantages.
Reproduction is the only reason any mutation survives.