The attempt to explain where humans come from has long preoccupied theologians, scientists, and laypeople alike. A new paper shows just how complicated our origin story could be. Written by scientists in Australia, South Africa, and Korea, the study uses DNA from individuals in southern Africa to track some of the oldest known genetic traces of so-called modern humans—people who looked like we do today. But though the paper zooms in on a northern Botswana river valley as the ancestral “homeland” of all modern humanity, other experts say there’s no such thing.
The new study looked at the mitogenome, or the mitochondrial DNA passed along the maternal line, of 200 living people from southern Africa. All are members of an ethnolinguistic indigenous group broadly known as the KhoeSan (unified by their traditional foraging way of life and use of languages that involve a unique “click” consonant), which previous genetic research suggests was once the largest group of people on the planet. Researchers examined their mitogenomes alongside others collected for earlier studies in the same region. Among the mitogenomes, they identified approximately 1,200 carriers of a single lineage known as L-0, and created the largest L-0 database to date.
Mitochondrial DNA, which is only passed on by mothers, is the focus of many studies of ancient human migration. While we get much of our DNA from both parents, which results in a mash-up that’s difficult to untangle while tracing the roots of a family tree, your mitochondrial DNA tells a single story: that of your mother, and her mother, and her mother’s mother. That creates a record that’s easier to track back in time. Mitochondrial DNA also mutates much faster than the rest of our genetic material, creating generation-to-generation changes researchers can use to track movements and meetings between groups of ancient people. It’s a way of understanding genetic change over centuries, rather than over millennia, and many researchers think it gives a clearer picture of our species’ family tree.
The authors of the new study compared different L-0 groups among the KhoeSan using these small shifts, and tracked the oldest of the bunch. Hayes and her colleagues propose that all modern humans are descended from the L-0 lineage, carried out of an ancestral “homeland” they’ve identified using geographic and historical climate data alongside information about the KhoeSan’s traditional territories.
On the basis of all this information the researchers propose that ancestral homeland of all anatomically modern humans is located in what is today northern Botswana. Hayes and her colleagues propose that the valley there, which is now quite dry, was the lush and fertile home of our ancestors for 70,000 years before a changing climate prompted them to spread out and begin humanity’s long trek around the world, taking with them their L-0 lineages, which spread out and differentiated.
“Our study demonstrates that our genetic maternal ancestors likely originated from a wetland region in Southern Africa—in present Botswana,” study author Axel Timmermann, a climate physicist at Pusan National University in Korea, told Popular Science in an email. “It also shows that climate played a fundamental role in setting in motion early human migrations, which contributed to the development of genetic diversity and eventually cultural and ethnic identity.”
It’s a compelling story, but the paper has already generated controversy. “The idea that we’re looking for a single origin [of anatomically modern humans] is out of fashion,” says John Hawks, a University of Wisconsin-Madison paleoanthropologist. That was the goal in the 1980s and ‘90s, Hawks says. But since then, modern genetic technologies have proven that our ancestors interbred with other species, such as Neanderthals, making the picture of humanity’s origin more complex than the Edenic story scientists sought to tell a few decades ago.
In other words, there was no one place or time when we suddenly became human. It’s probable that early “modern humans” travelled extensively and met, cohabitated, and mated with many other members of the genus Homo along the way. And although the river valley was apparently an inviting place in its prime, many other locations in Africa could have sustained modern humans at the same time. Today our ilk live in many different kinds of places, from the Arctic to the Sahara: There’s no reason to think that early humans didn’t do the same.
“I think the search for a single, tightly confined homeland of African Homo sapiens, within narrow environmental parameters, is a bit out of touch with the combined genomic, fossil, and paleoenvironmental data we now have,” Richard Potts, director of the Smithsonian Museum of Natural History’s Human Origins program, told Popular Science in an email interview.
But the intent of the study isn’t so bold, Timmermann told PopSci. “The message of our paper is that about 200,000 years ago the ancestors of the current L0 haplogroup emerged and lived in a vast wetland region northern Botswana,” he wrote. The study does not, however, “provide any information about where this group originally came from or what happened before 200,000 years ago.” This, Timmermann explained, is why the team used the word “homeland” and not “cradle.”
Beyond that, he writes, the fossil record tells us that many hominids closely related to Homo sapiens lived in Africa during the period they studied. Early humans could have met and cohabitated and mated with many of them. Although genetic traces of this history have yet to be found in modern human DNA, it’s possible they will be. There’s a lot more to say about our origins, but Hayes, Timmermann, and their fellow study authors are confident they’ve found at least one clear story. Many of their colleagues are less so.
While the interpretation of the data may leave room for debate, the new study still offers some value, says Hawks. “I think what it tells us is that we have to explore more parts of Africa for fossils and archaeology,” he says. Archaeologists have yet to find fossils of early modern humans in the areas this paper says they should be. Beyond that, he says, the work adds 200 new samples of mitochondrial DNA from a historically understudied group of people to the scientific record, which is valuable in and of itself. Today, only around 100,000 KhoeSan remain, and like many Indigenous peoples around the world, their language and way of life is threatened by racism and colonialism. Putting the KhoeSan on the genetic map might help raise their profile, and will certainly improve our understanding of the human genome. Most of the work focused on identifying genes and mutations both dangerous and beneficial has focused on caucasion people of European descent.
“We’re talking about people who, among the modern humans of the world, have been neglected in genetic samples,” he says. “Let’s make those communities a bigger part of understanding our past—and benefiting from genetic research.”
