Flesh­ing out an­ces­tral link to Ne­an­derthals

DNA found in an an­cient jaw­bone adds new de­tail to mod­ern hu­mans’ fam­ily tree.

Los Angeles Times - - THE NATION - By Eryn Brown eryn. brown@ latimes. com Twit­ter: @LATeryn­brown

Sci­en­tists have known that mod­ern hu­mans who live out­side Africa have a small amount of Ne­an­derthal DNA, but they haven’t been able to f lesh out when, where and how of­ten our early an­ces­tors mated with mem­bers of that now- ex­tinct branch of the hu­man fam­ily.

A new dis­cov­ery, an­nounced in the jour­nal Na­ture, adds a piece to the puz­zle. DNA test­ing of an an­cient jaw­bone has con­firmed that a man who lived in Ro­ma­nia about 40,000 years ago de­scended from a Ne­an­derthal just four to six gen­er­a­tions back — less than 200 years.

“To our amaze­ment, this guy had three or four times more Ne­an­derthal DNA than any mod­ern hu­man we had ever looked at,” said Svante Paabo, di­rec­tor of the Max Planck In­sti­tute for Evo­lu­tion­ary An­thro­pol­ogy in Leipzig, Ger­many, and co-se­nior au­thor of the study. “This is the first time we can say it’s dra­mat­i­cally more, and close in the fam­ily tree.”

The jaw­bone was dis­cov­ered in a Ro­ma­nian cave in 2002. Paabo’s anal­y­sis re­vealed that 6% to 9% of the man’s DNA came from Ne­an­derthals.

The sci­en­tists were able to f ig­ure out that one of those an­ces­tors had been very re­cent by ex­am­in­ing the size of the chunks of Ne­an­derthal DNA in the man’s genome.

When the body pro­duces an egg or a sperm, chro­mo­somes split up and re­or­ga­nize them­selves in a process called re­com­bi­na­tion. The fewer the gen­er­a­tions that have passed, the fewer such splits and re­or­ga­ni­za­tions will have oc­curred, and the longer the stretches of DNA con­trib­uted from an an­ces­tor will be.

The Ne­an­derthal DNA in the jaw­bone was “dis­trib­uted in big, big pieces on the chro­mo­some,” Paabo said. “This in­di­cates there has to be a Ne­an­derthal rel­a­tive very close in time.”

Sci­en­tists be­lieve that the Ne­an­derthal genes in peo­ple to­day were con­trib­uted early on, when mod­ern hu­mans an­ces­tral to all non-Africans mated with Ne­an­derthals in the Mid­dle East.

The new dis­cov­ery sug­gests that early Euro­peans also mated with Ne­an­derthals later in hu­man history, and prob­a­bly on their own turf.

The DNA also re­vealed that the jaw­bone’s owner was part of an an­cient pop­u­la­tion that is not re­lated to later Euro­pean groups ( in­clud­ing peo­ple liv­ing to­day).

The study was the latest of sev­eral in re­cent weeks that take ad­van­tage of im­proved an­a­lyt­i­cal tech­niques to probe an­cient DNA sam­ples.

The stud­ies in­clude a pair of re­ports de­tail­ing the pop­u­la­tion history of Bronze Age Europe; another de­ter­min­ing that the fa­mous Ken­newick man from Washington state is re­lated to Na­tive Amer­i­cans liv­ing to­day; and a dis­cus­sion of the evo­lu­tion of dogs gen­er­ated by study­ing DNA from a Siberian wolf that lived 35,000 years ago.

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