Human DNA tied largely to single exit

New studies say massive migration came out of Africa

NEW YORK — The genetic ancestry of people living outside Africa can be traced almost completely to a single exodus of humans from that continent long ago, new studies suggest.

Still, a tiny legacy from an earlier exit may persist in some native islanders in the southwestern Pacific Ocean.

That’s the conclusion from three studies of modern DNA from around the world, released by the journal Nature.

Our species, Homo

sapiens, arose about 200,000 years ago in Africa. From there, it colonized the world.

The new work takes advantage of the fact that human DNA accumulates tiny changes over time. That can be used like a clock to estimate how long ago two populations split off from each other. The approach can’t reveal every migration out of Africa, just those that left a genetic legacy that has been handed down to this day.

Scientists have long traced one such exit to a single population that left around 40,000 to 80,000 years ago, probably over time rather than all at once.

But some other work has turned up potential signs of a previous migration as early as 120,000 to 130,000 years ago.

One of the new papers says it found a trace of an earlier migration in native people of Papua New Guinea, which lies north of Australia.

At least 2 percent of their DNA may come from a population that split off from Africans about 120,000 years ago, reported researchers from the Estonian Biocentre in Tartu, Estonia, and other institutions.

The study analyzed the DNA of 483 people from 148 populations worldwide, including six Papuans.

The two other papers concluded that if there was a genetic contribution from an earlier migration, it must be tiny.