Past studies of human genetics have proposed the theory that modern humans originated from a single population in Africa. But a new paper, published last week in the journal Nature, put this idea to the test—and concluded it doesn’t hold up.
The paper relies on modeling using the genomes of 290 living people from southern, eastern and western Africa. The findings suggest that modern humans descended from at least two groups of ancient humans that were closely related and mixed genes on occasion, writes Live Science’s Charles Q. Choi.
“There is no single birthplace,” Eleanor Scerri, an evolutionary archaeologist at the Max Planck Institute for Geoanthropology in Germany who did not contribute to the study, tells the New York Times’ Carl Zimmer. “It really puts a nail in the coffin of that idea.”
Rather than envisioning human evolution as a tree—with a single stem that splits into disconnected branches—the researchers describe ancestral human populations as intertwining stems, writes Nature News’ Jude Coleman.
“All humans share relatively recent common ancestry, but the story in the deeper past is more complicated than our species evolving in just a single location or in isolation,” says lead author Aaron Ragsdale, a population geneticist at the University of Wisconsin–Madison, to Reuters’ Will Dunham.
For the new study, the researchers looked at genomic data from living humans, which included people from various groups: the Mende in Sierra Leone, the Nama in South Africa and the Amhara, Oromo and Gumuz groups in Ethiopia, according to Reuters. They also examined DNA from living Europeans and from the remains of a Neanderthal.
Jessica Thompson, a paleoanthropologist at Yale University who did not contribute to the research, tells National Geographic’s Tim Vernimmen that it might have been useful for the researchers to also include ancient DNA from Africa in the study. “People alive today may be quite different from those who lived in the same place in the past,” she tells the publication.
Using the modern DNA, the researchers modeled different explanations for today’s human diversity—including the single origin theory and the idea that Homo sapiens mixed with other early human species. But they found the scenario that best fit the DNA data was one in which humans had multiple points of origin.
“When we assume in our computer model that the stem population wasn’t quite as solid, but that parts of it would occasionally branch off and then later merge back together, we get a much better match with the genetic variation found in human populations today,” Ragsdale tells National Geographic.
The differences between these separate but intermingling groups would have been “almost as low as seen between contemporary human populations,” Simon Gravel, a co-author of the study and human geneticist at McGill University in Canada, tells Live Science.
The oldest fossils from early humans come from Africa, and the first modern humans likely came about around 315,000 years ago. Between 300,000 and 100,000 years ago, evidence of modern humans was spread throughout the continent—more support for the multiple origins theory, Scerri tells Nature News. Had humans originated in one spot, the oldest artifacts would be found there, with increasingly more recent remains found at sites emanating from the origin, but that is not the case, she tells the publication.