Where We Come From
Recent advances in genetics are starting to illuminate the wanderings of early humans
Enter Eve. In 1987, Allan Wilson, Rebecca Cann, and Mark Stoneking, researchers at the University of California-Berkeley, catapulted mitochondrial DNA into the headlines worldwide when they announced that they had traced it back 200,000 years to the oldest female ancestor of living humans--an African woman quickly dubbed Eve. Eve's debut rocked the archaeological community, which had been arguing for decades over whether modern humans evolved on more than one continent or instead swept out of Africa to replace more archaic hominids around the world. Wilson's group was attacked for sloppy science, and in fact there were problems with the original calculations. But genetic data from dozens of researchers have since almost universally supported the "Out of Africa" theory. "History has made a pretty consistent stamp on populations," says Lynn Jorde, a geneticist at the University of Utah, who has found African roots in nuclear DNA as well as in mitochondria and the Y. "Looking at more and more of the nuclear DNA is going to clarify the picture."
Questions remain about the nature of the early human diaspora. For instance, lively debate continues over whether Neanderthals and modern humans mated [box, Page 41]. And some remain skeptical about the Out of Africa theory itself. This month researchers at Australian National University published the results of mitochondrial DNA testing on a 60,000-year-old skeleton called Lake Mungo 3. The DNA didn't match that of living humans, suggesting that the Mungo lineage evolved in Australia, not Africa. But it could simply mean that the Mungo lineage went extinct, as have many others.
Indeed, there have been many Adams, and many Eves. The genetic record reflects only those whose offspring survived and reproduced. For instance, the earliest forefather identified so far is 20,000 to 30,000 years younger than Eve. "It's rather distressing to find that Eve could not be the wife of Adam," says Luigi Luca Cavalli-Sforza, a professor emeritus at Stanford University and pioneer of population genetics. The bulk of the genetic data suggests that a small population of modern humans, as few as 10,000, left Africa 100,000 or so years ago, wandering into the Middle East and on to Asia and Europe. Their genetic footprints lead all the way to Tierra del Fuego.
Emory's Wallace has spent the past decade tracking mitochondrial markers from Africa to Asia and the Americas--and fueling a robust dispute over just when humans first arrived in the New World. For much of the past 50 years, archaeologists thought that people tramped across the Bering Land Bridge and through a gap in the glaciers about 14,000 years ago. But Wallace thinks there were other migrations, one as early as 30,000 years ago. Archaeological sites in Pennsylvania, Virginia, and Chile support this earlier migration, although the notion remains hotly contested. Wallace's newest and most surprising discovery is a set of genetic markers found only in the Ojibwa and other tribes living near the Great Lakes; the markers are not found in any other native Americans or in Asia. "We just don't know how it got there," Wallace says, "but it's clearly related to the European population." The simple answer would be that the DNA arrived with European colonists, but the strain is different enough from the existing European lineage that it must have left the Old World long before Columbus. The lineage could have passed through Asia and later died out there. But Dennis Stanford, a paleoarchaeologist at the Smithsonian Institution, says this mystery strain, dubbed Haplogroup X, bolsters his theory that a hardy band of Europeans left Iberia and navigated the North Atlantic ice pack 15,000 years ago. "During colder time periods the sea ice was as far south as the Bay of Biscay," Stanford says, adding that the ice edge would have been ideal for hunting and fishing, just as it is in the Arctic today.
advertisement
