One wave of ancient human migrants out of Africa gave rise to all non-Africans alive today, three separate genetic studies conclude.
Those human explorers left Africa about 50,000 to 72,000 years ago, mixed with Neandertals and spread across the world, researchers report online September 21 in Nature. The studies present data from genetically diverse and previously unrepresented populations. Together they offer a detailed picture of deep human history and may settle some long-standing debates, but there is still room to quibble. All non-Africans stem from one major founding population, the studies agree, but earlier human migrations are also recorded in present-day people’s DNA, one study finds. And a fourth study in the same issue of Nature, this one focusing on ancient climate, also makes the case for an earlier exodus.
Scientists have long debated when anatomically modern humans first trekked out of Africa and how many waves of migration there were. Archaeological evidence indicates there were modern humans in Asia by at least 80,000 years ago. Human DNA in a Neandertal woman from Siberia indicates humans interbred with Neandertals outside Africa as long as 110,000 years ago (SN: 3/19/16, p. 6). But those people died out and didn’t contribute DNA to later generations, says Swapan Mallick, an evolutionary geneticist at Harvard Medical School and coauthor of a paper that traced the genetic history of 300 people from 142 populations around the world. The ancestors of today’s non-Africans probably left Africa about 50,000 years ago, Mallick and colleagues calculate.
Going global
Previous studies have used fossil, archaeological and genetic data to time human’s colonization of the world (times shown below). New genetic studies may change that map; they suggest small numbers of people left Africa 120,000 years ago, but left little trace in the DNA of present-day people. Most non-Africans inherited their DNA from people who left Africa between about 70,000 and 50,000 years ago, new studies suggest. But a climate study indicates that was the worst possible time for an out-of-Africa migration and suggests people may have left earlier, between 80,000 and 100,000 years ago.
Data in another study reveal remnants of a much earlier exodus from Africa that persist in the genomes of present-day Papuans, biological anthropologist Luca Pagani of the Estonian Biocentre in Tartu and colleagues report. About 2 percent of the genome of Papuans can be traced back to small bands of humans who left Africa 120,000 years ago. “This expansion was successful in leaving descendants today,” Pagani says. But a massive wave of migrants who left Africa after about 75,000 years ago probably overwhelmed that small trickle, swamping out their genetic signature.
A third study focusing on the genetic history of aboriginal Australians and Papuans from the New Guinea highlands didn’t find traces of a 120,000-year-old migration, but didn’t rule it out either, says study coauthor Eske Willerslev, an evolutionary geneticist at the University of Copenhagen.