"Long before it's in the papers"
January 27, 2015


Europeans have evolved lighter skin in past 5,000 years, study finds

March 11, 2014
Courtesy of Jo­han­nes Gu­ten­berg Uni­vers­ity Mainz
and World Science staff

Eu­ro­peans have evolved light­er skin, eyes and hair in past 5,000 years, a new study finds.

The skin changes may be a re­sult of the body’s need to pro­duce more Vit­a­min D in lower-sun­light ar­eas, al­though the oth­er changes are harder to ex­plain, sci­en­tists said.

An­thro­po­l­o­gists at Jo­han­nes Gu­ten­berg Uni­vers­ity Mainz in Ger­ma­ny and ge­neti­cists at Uni­vers­ity Col­lege Lon­don, work­ing with ar­chae­o­lo­gists from Ber­lin and Ki­ev, reached the con­clu­sions based on anal­y­sis of an­cient DNA from skele­tons.

The find­ings, pub­lished this week in the jour­nal Pro­ceed­ings of the Na­t­ional Acad­e­my of Sci­ences, sug­gest the changes weren’t ran­dom, but were the re­sult of nat­u­ral se­lec­tion—nat­ur­al pres­sures that drive ev­o­lu­tion, pos­sibly in­clud­ing mat­ing pref­er­ences.

The sci­en­tists com­pared the old DNA da­ta with that of con­tem­po­rary Eu­ro­peans us­ing com­put­er sim­ula­t­ions. Where the ge­net­ic changes could not be ex­plained by the ran­domness of in­her­it­ance, the re­search­ers in­ferred that se­lec­tion played a role.

While in­ves­ti­gat­ing many ge­net­ic “mark­ers” in ar­chae­o­log­i­cal and liv­ing in­di­vid­u­als, San­dra Wilde of Mainz Uni­vers­ity said she no­ticed strik­ing dif­fer­ences in genes as­so­ci­at­ed with hair, skin, and eye pig­menta­t­ion. 

“All our early an­ces­tors were more darkly pig­mented,” Wilde said. “The darker phe­no­type [ap­pear­ance] seems to have been pre­ferred by ev­o­lu­tion over hun­dreds of thou­sands of years,” she added, but things must have changed in the last 50,000 years as hu­mans be­gan to mi­grate north­ward.

“In Eu­rope we find a par­tic­u­larly wide range of ge­net­ic varia­t­ion in terms of pig­menta­t­ion,” added co-au­thor Karola Kir­sanow, al­so at Mainz Uni­vers­ity. “How­ever, we did not ex­pect to find that nat­u­ral se­lec­tion had been fa­vor­ing light­er pig­menta­t­ion over the past few thou­sand years.” 

The sig­nals of se­lec­tion the sci­en­tists iden­ti­fied are, they said, among the most pro­nounced that have been disco­vered to date in the hu­man ge­nome.

“Per­haps the most ob­vi­ous [ex­plana­t­ion] is that this is the re­sult of adapta­t­ion to the re­duced lev­el of sun­light in north­ern lat­i­tudes,” said co-researcher Mark Thom­as of Uni­vers­ity Col­lege Lon­don. “Most peo­ple of the world make most of their vit­a­min D in their skin as a re­sult UV ex­po­sure. But at north­ern lat­i­tudes and with dark skin, this would have been less ef­fi­cient. If peo­ple weren’t get­ting much vit­a­min D in their di­et, then hav­ing light­er skin may have been the best op­tion.”

“But this vit­a­min D ex­plana­t­ion seems less con­vinc­ing when it comes to hair and eye col­or,” Wilde con­tin­ued. “In­stead, it may be that light­er hair and eye col­or func­tioned as a sig­nal in­di­cat­ing group af­filia­t­ion, which in turn played a role in the se­lec­tion of a part­ner.” Sex­u­al se­lec­tion of this kind is com­mon in an­i­mals and may al­so have been one of the driv­ing forc­es be­hind hu­man ev­o­lu­tion over the past few mil­len­nia.

“We were ex­pecting to find that changes in the hu­man ge­nome were the re­sult of popula­t­ion dy­nam­ics, such as migra­t­ion. In gen­er­al we ex­pect ge­net­ic changes due to nat­u­ral se­lec­tion to be the ex­cep­tion rath­er than the rule. At the same time, it can­not be de­nied that lac­tase per­sis­tence, i.e., the abil­ity to di­gest the main sug­ar in milk as an adult, and pig­menta­t­ion genes have been fa­vored by nat­u­ral se­lec­tion to a sur­pris­ing de­gree over the last 10,000 years or so,” added Jo­a­chim Burg­er at Mainz, sen­ior au­thor of the stu­dy. 

“But it should be kept in mind that our find­ings do not nec­es­sarily mean that eve­ry­thing se­lected for in the past is still ben­e­fi­cial to­day. The char­ac­ter­is­tics hand­ed down as a re­sult of sex­u­al se­lec­tion can be more of­ten ex­plained as the re­sult of pref­er­ence on the part of in­di­vid­u­als or groups rath­er than adapta­t­ion to the en­vi­ron­ment.”

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Europeans have evolved lighter skin, eyes and hair in past 5,000 years, a new study finds. The skin changes may be a result of the body’s need to produce more vitamin D in lower-sunlight areas, although the other changes are harder to explain, scientists said. Anthropologists at Johannes Gutenberg University Mainz in Germany and geneticists at University College London, working with archaeologists from Berlin and Kiev, reached the conclusions based on analysis of ancient DNA from skeletons. The findings, published in the journal Proceedings of the National Academy of Sciences, suggest the changes weren’t random, but were the result of natural selection—environmental pressures that drive evolution, possibly including mating preferences. The scientists compared the old DNA data with that of contemporary Europeans using computer simulations. Where the genetic changes could not be explained by the randomness of inheritance, the researchers inferred that positive selection played a role. While investigating numerous genetic markers in archaeological and living individuals, Sandra Wilde of Mainz University said she noticed striking differences in genes associated with hair, skin, and eye pigmentation. “All our early ancestors were more darkly pigmented,” Wilde said. “The darker phenotype [appearance] seems to have been preferred by evolution over hundreds of thousands of years,” she added, but things must have changed in the last 50,000 years as humans began to migrate northward. “In Europe we find a particularly wide range of genetic variation in terms of pigmentation,” adds co-author Karola Kirsanow, also at Mainz University. “However, we did not expect to find that natural selection had been favoring lighter pigmentation over the past few thousand years.” The signals of selection the scientists identified are, they said, among the most pronounced that have been discovered to date in the human genome. “Perhaps the most obvious [explanation] is that this is the result of adaptation to the reduced level of sunlight in northern latitudes,” said co-researcher Mark Thomas of University College London, corresponding author of the study. “Most people of the world make most of their vitamin D in their skin as a result UV exposure. But at northern latitudes and with dark skin, this would have been less efficient. If people weren’t getting much vitamin D in their diet, then having lighter skin may have been the best option.” “But this vitamin D explanation seems less convincing when it comes to hair and eye color,” Wilde continues. “Instead, it may be that lighter hair and eye color functioned as a signal indicating group affiliation, which in turn played a role in the selection of a partner.” Sexual selection of this kind is common in animals and may also have been one of the driving forces behind human evolution over the past few millennia. “We were expecting to find that changes in the human genome were the result of population dynamics, such as migration. In general we expect genetic changes due to natural selection to be the exception rather than the rule. At the same time, it cannot be denied that lactase persistence, i.e., the ability to digest the main sugar in milk as an adult, and pigmentation genes have been favored by natural selection to a surprising degree over the last 10,000 years or so,” added Joachim Burger at Mainz, senior author of the study. “But it should be kept in mind that our findings do not necessarily mean that everything selected for in the past is still beneficial today. The characteristics handed down as a result of sexual selection can be more often explained as the result of preference on the part of individuals or groups rather than adaptation to the environment.”