early history in Africa is coming into sharper focus with a new study
of 180 genomes from a dozen ethnic groups on the continent —
some of which have never before been analyzed.
preliminary results suggest that more than 40,000 years ago, two of
the groups — the San and the Baka Pygmy — were roughly
twice the size of other ethnic groups present at the time, and that
the San and Baka overlapped in central-eastern or southern Africa.
Researchers presented these as-yet unpublished results at an American
Society of Human Genetics (ASHG) meeting in San Diego, California,
is the most comprehensive whole-genome sequencing from groups that
represent the ancestral diversity of humans, says Sarah Tishkoff, a
human geneticist at the University of Pennsylvania in Philadelphia, who
co-led the project. Together with genetic analyses of ancient human
remains from Africa published last year, the latest data are
starting to fill in the nearly blank canvas of early human history.
Homo sapiens originated in Africa roughly 250,000 to 315,000
years ago, geneticists have devoted their attention almost
exclusively to the small subset of Africans that migrated north to
Europe tens of thousands of years later. A handful of African
genomics projects are now beginning to address this imbalance.
In 2009, Tishkoff and her colleagues published a study
assessing small sections of the genome from people belonging to about
100 of the more than 2,000 ethnic groups in Africa today. The results
suggested that the San and the Baka might have descended from a single
lineage of hunter-gatherers. But Tishkoff needed whole genomes from
them and other ethnic groups to test this idea.
team spent years getting approvals for the project from government
and institutional ethical review boards in countries in eastern,
southern and western Africa. Tishkoff and her colleagues partnered
with local researchers and spoke about genetics with the communities
that they hoped to enrol in the project, explaining what the
scientists and the groups could learn about their early ancestry.
Many of the communities live in remote regions — such as the
Sabue people of southwestern Ethiopia — and geneticists know
little about them.
research in Africa can be contentious, and many scientists engage in
such outreach to involve the communities they work with in the
research. The Human Heredity and Health in Africa (H3Africa) Initiative
— an African-led consortium that supports genomics research — has called for a more substantive role for Africa-based scientists
in such projects. And last year, an Indigenous group in South Africa
introduced research-ethics guidelines for scientists looking to work
and her colleagues make sure to follow up with the communities that
participate in their studies. Some of the Fulani, a traditionally
nomadic group, are interested in what their genetics can reveal about
their migration history, says Alfred Njamnshi, a neurologist at the
University of Yaoundé in Cameroon. The last time he visited
one community, he spoke with an elderly Fulani man who recalled
walking 3,000 kilometres from Senegal to Cameroon as a child and told
Njamnshi stories of his parents’ travels.
one-fifth of the genetic variation that the team uncovered has never
before been reported. Statistical models of the data indicate that
the Hadza and the Sandawe people of Tanzania shared an ancestor in
the past 30,000 years.
findings also suggest that there was intermingling during that period
between the Hadza, the San in southern Africa and the Baka in central
Africa, all of whom were traditionally hunter-gatherers. “I
think we are seeing an ancient common ancestry between the major
hunter-gatherer groups in Africa,” Tishkoff says.
of the findings align with signals of mixed Hadza and San ancestry in
DNA extracted from 2,500- to 8,100-year-old human remains1, says Pontus
Skoglund, a palaeogeneticist at the Francis Crick Institute in London.
“I had been thinking about an interconnected hunter-gatherer population
stretching from present-day Tanzania to South Africa.”
researchers want to see further statistical analyses of the data
before they accept the notion that the Hadza, San and Baka overlapped
geographically. Earlier studies have given little indication that
people from these groups mixed with each other, says Deepti
Gurdasani, a genetic epidemiologist at the Wellcome Sanger Institute
in Hinxton, UK. But it’s plausible, she adds. “There is
literally nothing in Africa that is not possible since we have no
idea what humans were doing on the continent 5,000 years ago.”
knowledge gap might dissipate in the coming years as more teams
working on African genome projects publish their results. Gurdasani
presented results from an analysis of whole genomes from 2,000
individuals from Uganda at the ASHG meeting last week. And H3Africa
has sequenced more than 400 genomes from African individuals, says
Charles Rotimi, a Nigerian genetic epidemiologist at the National
Human Genome Research Institute in Bethesda, Maryland, who founded
conducting further analyses, Tishkoff plans to publish the results
and share the anonymized genomes publicly, so that scientists can
pool their data. This last bit is essential, says Shaohua Fan, a
molecular biologist now at Fudan University in Shanghai, China. As of
2016, about 80% of people in genetic studies were of European descent.
“We know humans originate in Africa,” says Fan, “but we don’t know what
we did before we left — we don't know our own history.”
This commentary was originally published by Nature.com