A new study of human genetic variation in sub-Saharan Africa, where modern Homo sapiens are believed to have originated, helps to reveal the region’s rich genetic history.
According to Carina Schlebusch from Uppsala University in Sweden and colleagues from around the world, the click-speaking Khoe-San people, whose genetic divergence from other African groups is considered to be one of the earliest in modern human history, broke off from other populations approximately 100,000 years ago.
This split took place well before modern humans migrated out of Africa, and the initial Khoe-San population eventually diversified into a northern and southern group about 35,000 years ago, they say.
Khomani San settlement near Askham in the Northern Cape Province, South Africa. | Image courtesy of Dr. Carina Schlebusch
The study does not indicate one specific geographic location from which modern humans arose. Instead, the researchers discovered a complex record of distinct genetic sub-Saharan populations that sometimes intermingled.“As the cradle of humanity, Africa has long been studied to help us understand the evolution and diversity of modern-day humans,” said Laura Zahn, senior editor at the journal Science, during a 19 September press teleconference about the research. “The Schlebusch report has now investigated the genetic diversity of over 200 African individuals representing a swath of populations believed to represent some of the earliest diverging lineages of humans.”Schlebusch and her colleagues examined the genetic variants of 220 individuals from 11 different populations across southern Africa and explored their relationships and commonalities. Their study appears in the 20 September issue of the journal Science online, at the Science Express Web site.“We date this deep divergence to about—or at least—100,000 years ago,” said Mattias Jakobsson, from Uppsala University in Sweden, the senior author of the Science report. This means that the Khoe-San split occurred twice as long ago as the next oldest divergence of modern humans, which was between Central African hunter-gatherer groups and other African populations.
The researchers’ genomic study also detected genes that were likely under selection at the time of the Khoe-San’s divergence from other African groups. They included those involved with skeletal development, such as bone and cartilage growth, as well as immune system and neuronal function.
“Different parts of Africa show up as potentially being the origin of anatomically modern humans,” said Jakobsson. “So that leads us to postulate that, potentially, modern humans arose from a… non-homogenous group that different groups of humans contributed genes to. Later on, this pool became anatomically modern humans.”
The findings shed light onto the ways in which modern human populations around the world arose from a complex evolutionary history in Africa—and it suggests that similar genomic studies could unlock more secrets surrounding the origins of modern humans.
Co-author Himla Soodyall, a professor at the University of the Witwatersrand in Johannesburg, South Africa, said similar studies “will allow us to get a better window into the past to find out why humans moved around.”
Brandon Bryn and Natasha Pinol
20 September 2012