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Scientists: genome data suggests we mixed with Neanderthals

May 6, 2010
Courtesy Science
and World Science staff

Sci­en­tists are re­port­ing that they have de­cod­ed more than half the Ne­an­der­thal ge­nome, and that the da­ta sup­ports a the­o­ry that our an­cest­ors in­ter­bred with Ne­an­der­thal peo­ple a lit­tle.

The sci­en­tists de­vised a draft ge­nome se­quence, or a list of the “let­ters” in a crea­ture’s ge­ne­tic code. These “let­ters” con­sist of mo­lec­u­lar un­its called nu­cleotides that make up the DNA. An anal­y­sis of this se­quence can re­veal in­forma­t­ion about an or­gan­is­m’s an­ces­try.

Vin­dija Ca­ve, Cro­a­tia, where the three bones used in the anal­y­sis were found. (Im­age cour­te­sy Jo­han­nes Krause, MPI/EVA)

Sci­en­tists used pill-sized sam­ples of pow­der from three bones of Ne­an­der­thals, a stocky an­cient breed of hu­mans that co-ex­isted wth an­ces­tors of mod­ern hu­mans. The find­ings ap­pear in the May 7 is­sue of the re­search jour­nal Sci­ence. 

The re­search­ers, led by Svante Pääbo of the Max Planck In­sti­tute for Ev­o­lu­tion­ary An­thro­po­l­ogy in Leip­zig, Ger­ma­ny, com­pared the Ne­an­der­thal ge­nome with ge­nomes of five pre­s­ent-day hu­mans.

The re­sults al­so re­vealed var­i­ous genes that are un­ique to mod­ern peo­ple, the sci­en­tists said, in­clud­ing a hand­ful of genes that spread rap­idly among our spe­cies af­ter we split from a com­mon an­ces­tor we shared with Ne­an­der­thals. Among these genes are three be­lieved to af­fect men­tal and cog­ni­tive de­vel­op­ment; de­fects in these genes are linked to con­di­tions such as Down syn­drome, schiz­o­phre­nia and au­tism.

“For the first time we can now iden­ti­fy ge­net­ic fea­tures that set us apart from all oth­er or­gan­isms, in­clud­ing our clos­est ev­o­lu­tion­ary rel­a­tives,” Ne­an­der­thals, said Pääbo. “This [work] really just hints at what genes one should now stu­dy, and I’m sure we and many oth­er groups will be do­ing that.”

Ne­an­der­thals first ap­peared around 400,000 years ago, ranged across Eu­rope and west­ern Asia, and died out about 30,000 years ago. The draft Ne­an­der­thal ge­nome se­quence be­ing re­ported rep­re­sents about 60 per­cent of the ge­nome; the da­ta was worked out us­ing bones found in a cave in Cro­a­tia. 

Pääbo and col­leagues al­so se­quenced the ge­nomes of five pre­s­ent-day hu­mans from south­ern Af­ri­ca, West Af­ri­ca, Pap­ua New Guin­ea, Chi­na and France, to com­pare with the Ne­an­der­thal ge­nome.

The Ne­an­der­thal ge­nome proved slightly more si­m­i­lar to those of the non-Af­ri­can peo­ple than Af­ri­cans, said the in­ves­ti­ga­tors. One of the sim­plest sce­nar­i­os to ex­plain this and some pre­vi­ous da­ta, they added, is that af­ter mod­ern hu­mans mi­grat­ed out of Af­ri­ca, they en­coun­tered and in­ter­bred with Ne­an­der­thals in the Mid­dle East. The han­ky-pan­ky seems to have been fairly lim­it­ed, judg­ing from the extent of the si­m­il­ar­ities, but “it’s cool to think that some of us have a lit­tle Ne­an­der­thal DNA in us,” Pääbo said.

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Scientists are reporting that they have decoded most of the Neanderthal genome, and that the data supports a theory that Neanderthals and humans interbred a little. The scientists devised a draft genome sequence, or a list of the “letters” in a creature’s genome, which consist of molecular units called nucleotides that make up the DNA. An analysis of this sequence can reveal information about an organism’s ancestry. Scientists used pill-sized samples of bone powder from three bones of Neanderthals, a stocky ancient breed of humans that used to co-exist wth modern humans in Europe and western Asia. The findings appear in the 7 May issue of the research journal Science. The researchers, led by Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, compared the Neanderthal genome with the genomes of five present-day humans from different parts of the world. The results also revealed various genes that are unique to humans, the scientists said, including a handful that spread rapidly among our species after humans and Neanderthals split from a common ancestor. Among these are three genes believed to affect mental and cognitive development; mutations in these genes are linked to conditions such as Down syndrome, schizophrenia and autism. “For the first time we can now identify genetic features that sets us apart from all other organisms, including our closest evolutionary relatives,” said Pääbo. “This [work] really just hints at what genes one should now study, and I’m sure we and many other groups will be doing that.” Neandertals are our closest evolutionary relatives. They first appeared around 400,000 years ago, ranged across Europe and western Asia, and died out about 30,000 years ago. The draft Neandertal genome sequence being reported represents about 60 percent of the genome; the data was worked out using bones found in a cave in Croatia. Pääbo and colleagues also sequenced the genomes of five present-day humans from southern Africa, West Africa, Papua New Guinea, China and France, to compare with the Neanderthal genome. The Neandertal genome proved slightly more similar to those of the non-African people than Africans, said the investigators. One of the simplest scenarios to explain this and some previous data, they added, is that after modern humans migrated out of Africa, they encountered and interbred with Neanderthals in the Middle East. This activity interbreeding seems to have been fairly limited, based on the but “it’s cool to think that some of us have a little Neandertal DNA in us,” Pääbo said.