"Long before it's in the papers"
June 04, 2013

RETURN TO THE WORLD SCIENCE HOME PAGE


A common ancestor for all blue-eyed people

Jan. 31, 2008
Courtesy University of Copenhagen
and World Science staff

New re­search has found that blue-eyed peo­ple have one, com­mon an­ces­tor who lived be­tween 6,000 and 10,000 years ago. At some point then—a time by which hu­mans were in most of Earth’s liv­a­ble ar­eas, ag­ri­cul­ture was spread­ing and the first civ­il­iz­a­tions were form­ing—a muta­t­ion pro­duced blue eyes, Un­ivers­ity of Co­pen­ha­gen bi­ol­o­gists say

A single genetic mutation is responsible for all the blue-eyed people alive today, a study proposes. (Image © Lucretious 2005)


“O­rig­i­nally, we all had brown eyes,” said one of the re­search­ers, Hans Eiberg. But a muta­t­ion af­fect­ing a gene called OCA2 “re­sulted in the crea­t­ion of a ‘switch’ which lit­er­ally turned off the abil­ity to pro­duce brown eyes.” 

The gene, he ex­plained, codes for the pro­duc­tion of a pro­tein in­volved in pro­duc­ing mel­a­nin, the pig­ment that gives colour to our hair, eyes and skin. 

The “switch” is lo­cat­ed not with­in the gene, but in a di­rectly neigh­bor­ing gene; yet it in­flu­ences OCA2, Eiberg said. The re­sult is a re­duc­tion in the pro­duc­tion of mel­a­nin in the iris—ef­fec­tively “di­lut­ing” brown eyes to blue, Eiberg went on. If it turned off mel­a­nin pro­duc­tion com­plete­ly, he said, it would pro­duce al­bi­nos, or peo­ple with­out pig­ment in their hair, skin or eyes.

The find­ings ap­pear in the Jan. 3 on­line is­sue of the re­search jour­nal Hu­man Ge­net­ics.

Eye colour varia­t­ion from brown to green is all caused by the amount of mel­a­nin in the iris of the eye, Eiberg ex­plained, but the blue-eyed have only slight varia­t­ion in this amount. “From this we can con­clude that all blue-eyed in­di­vid­u­als are linked to the same an­ces­tor… they have all in­her­it­ed the same switch at ex­actly the same spot in their DNA.” Un­like them, brown-eyed peo­ple vary con­sid­erably in the ar­ea of their DNA that con­trols mel­a­nin pro­duc­tion, he added.

Eiberg and col­leagues ex­am­ined DNA from the mi­to­chon­dria, a cel­lu­lar com­part­ment passed down only through moth­ers. They al­so com­pared eye colour of blue-eyed peo­ple from in coun­tries as di­verse as Jor­dan, Den­mark and Tur­key. The find­ings are the lat­est in a dec­ade of ge­net­ic re­search that Eiberg said be­gan in 1996, when he first im­pli­cat­ed the OCA2 gene in eye colour.

The muta­t­ion of brown eyes to blue is nei­ther pos­i­tive nor neg­a­tive, Eiberg said; rath­er, it’s one of sev­er­al muta­t­ions such as hair colour, bald­ness, freck­les and beau­ty spots, which nei­ther raise nor re­duce a per­son’s sur­viv­al chances. “It simply shows that na­ture is con­stantly shuf­fling the hu­man genome,” he said, “cre­at­ing a ge­net­ic cock­tail of hu­man chro­mo­somes and try­ing out dif­fer­ent changes.”


* * *

Send us a comment on this story, or send it to a friend

 

Sign up for
e-newsletter
   
 
subscribe
 
cancel

On Home Page         

LATEST

  • Meet­ing on­line may lead to hap­pier mar­riages

  • Pov­erty re­duction, environ­mental safe­guards go hand in hand: UN re­port

EXCLUSIVES

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?

  • Diff­erent cul­tures’ mu­sic matches their spe­ech styles, study finds

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

New research has found that blue-eyed people have one, common ancestor who lived between 6,000 and 10,000 years ago. At some point then—when humans had entered most of Earth’s livable areas, agriculture was spreading and the first civilizations were forming—the mutation produced blue eyes, University of Copenhagen biologists say “Originally, we all had brown eyes,” said one of the researchers, Hans Eiberg. But a mutation affecting a gene called OCA2 “resulted in the creation of a ‘switch’ which literally turned off the ability to produce brown eyes.” The gene codes for the production of a protein involved in producing melanin, the pigment that gives colour to our hair, eyes and skin. The “switch” is located not within the gene, but in a directly neighboring gene; yet it influences OCA2, Eiberg said. The result is a reduction in the production of melanin in the iris—effectively “diluting” brown eyes to blue, Eiberg went on. If it turned off melanin production completely, he said, it would produce albinos, or people without pigment in their hair, skin or eyes. The findings appear in the Jan. 3 online issue of the research journal Human Genetics. Eye colour variation from brown to green is all caused by the amount of melanin in the iris of the eye, Eiberg explained, but the blue-eyed have only slight variation in this amount. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor… they have all inherited the same switch at exactly the same spot in their DNA.” Unlike them, brown-eyed people vary considerably in the area of their DNA that controls melanin production, he added. Eiberg and colleagues examined DNA from the mitochondria, a cellular compartment passed down only through mothers. They also compared eye colour of blue-eyed people from in countries as diverse as Jordan, Denmark and Turkey. The findings are the latest in a decade of genetic research that Eiberg said began in 1996, when he first implicated the OCA2 gene in eye colour. The mutation of brown eyes to blue is neither positive nor negative, Eiberg said; rather, it’s one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither raise nor reduce a person’s survival chances. “It simply shows that nature is constantly shuffling the human genome,” he said, “creating a genetic cocktail of human chromosomes and trying out different changes.”