Ancient Hook-ups, All Over the World

You think you have big travel plans for the Memorial Day weekend? I guarantee they're nothing like what the first humans managed as they walked all over the globe after leaving their African homeland.

The human genome project has been a veritable treasure trove for scientists trying to tell the story of humankind’s migrations out of Africa. A couple of terrific books have chronicled this, and the use of genetics to reconstruct human history was a focus of a cover story we did last year. The fun part is when genetics throws a wrench into supposedly settled accounts, and that’s what a paper posted today in the open-access journal PLoS Genetics does.

In it, scientists from the University of Oxford and University College Cork describe a new technique they developed. It analyzes not just the Y chromosome, as many studies using genetics to trace human history do, but parts of chromosomes across the entire human genome. The details are complicated, but the bottom line is an ability to probe further back in time and identify smaller genetic contributions.

The technique confirms the out-of-Africa model, in which all human populations outside that continent today are the descendants of a single pulse of wanderers who left Africa. Hominids who originally lived in the regions of Asia and Europe colonized by the migrants contributed nothing to the modern gene pool, which is a polite way of saying that our ancestors wiped them all out (or at least prevented them from mating). Or, as I wrote in the cover story:

“The first modern humans—and therefore, unlike the earlier wave of Homo erectus into Asia a million years ago, the ancestors of everyone today outside Africa—departed Africa about 66,000 years ago. These pilgrims were strikingly few.... The best estimate: 2,000 men. Assuming an equal number of women, only 4,000 brave souls ventured forth from Africa.”

Now the technique is throwing up surprises about what happened next. Among them:

*The most northerly East Asian population that the scientists analyzed, Siberians called the Yakut, carry genes of the most northerly European population, the Orcadians (whose descendants live in the Orkney Islands), suggesting that northern Europeans walked into north Asia and hooked up with native peoples there.

*Populations in Central Eurasia have genes from the Near East (Bedouins and Palestinians) and even Kenyan Bantus.

*In Europe, the most ancient populations are the French, followed by the Tuscans and then other Italians, all of whom trace their ancestry to north Africans called Mozabites, today called Berbers, and to several Near Eastern and Central Asian populations. Europeans have more genetic ancestors than any non-European population, making Europe the world’s true melting pot.

*The youngest Europeans are the Sardinians, Russians, Orcadians and Basques—which makes sense, since they are all at the geographic extremes of the continent. People arrived there last. All four have big genetic contributions from the Near East and Central Asia, suggesting multiple waves of migrants into Europe.

*In the Americas, the Colombians are the oldest population. They can trace 47 percent of their ancestry to the Hazara of East Asia but, oddly, they also have genetic contributions from the French. That probably reflects intermarriage after Europeans arrived in the New World.

*The Pima are the oldest people of North America. They trace their ancestry to the Colombians but also, surprisingly, to Mongolians, who are not ancestors of the Colombians. That suggests multiple distinct colonizations into North America from Asia.

*The Mayans have Bantu and Tuscan donors, presumably due to intermarriage after the Europeans arrived.

For two cool little movies of all this, scroll to the bottom of the paper and click on Movie 1 and Movie 2.