Africans’ genes mute on human birthplace
The origin story for Homo sapiens is a messy tale. Rather than emerging from one small population, the human species likely evolved from a dispersed, complex network of groups that mixed and mated with each other, scientists report online September 20 in Science.
The new research is one of the largest genetic studies of southern Africa’s click-speaking hunter-gatherers known as the Khoisan. Sometimes called Bushmen, the Khoisan are the world’s most genetically diverse people and diverged from other populations very early in human history.
The new work dates the genetic split between the Khoisan and the rest of humankind to at least 100,000 years ago, which is in line with other estimates. That’s 55,000 years older than the next branch on the human family tree, when Central African pygmies split off. The researchers also found that the Khoisan divided into a northern and a southern group approximately 35,000 years ago.
But when the scientists looked for genetic clues pointing to where in sub-Saharan Africa humankind began, they couldn’t trace modern groups back to any one region. That suggests early humans came from a highly structured population with genetic exchange between subgroups.
“The complexity of the South African population is the big story,” says Adam Siepel, a computational biologist at Cornell University. “It undermines simpler stories trying to pinpoint a single geographic origin of modern humans.” Previous fossil evidence had suggested East Africa while smaller genetic analyses indicated South Africa.
In the new study, Carina Schlebusch of Sweden’s Uppsala University and colleagues looked at single nucleotide polymorphisms, or SNPs, which are locations in the genetic code where people commonly differ. The researchers surveyed 2.3 million SNPs in 220 individuals from 11 African populations, including seven Khoisan groups. After combining the new data with previously published data, the team assessed four measures of genetic variation to find where in Africa humans originated, but the results didn’t converge on one location.
Read the full article at: sciencenews.org
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