For generations, the story of modern humans has centered on a single ancestral population somewhere in Africa. From there, branches were thought to split off, spread across the continent, and eventually migrate out. But new genetic research from UC Davis reveals a far more complex picture of human origins in Africa.
This doesn’t debunk our African roots. The shift is in the details: our ancestors likely didn’t descend from one isolated group. Instead, early Homo sapiens probably emerged from several related populations living simultaneously—drifting apart, then mixing again over vast timescales.
Human Ancestors Split Apart but Kept Mixing Across Africa
Led by UC Davis anthropology professor Brenna Henn, the team tested multiple human evolution models. They compared genetic data from southern, eastern, and western Africa with fossil evidence of early Homo sapiens. Here’s the challenge: bones and DNA often tell conflicting stories.
“This uncertainty is due to limited fossil and ancient genomic data, and to the fact that the fossil record does not always align with expectations from models built using modern DNA,” she said. “This new research changes the origin of species.”
The new model rejects a single, sealed-off African population. Instead, several related Homo populations coexisted for hundreds of thousands of years. They weren’t identical but similar enough to interbreed when paths crossed.
People moved constantly, groups encountered each other, and genes flowed freely between them. Researchers now describe human origins not as a neat family tree, but as a tangled network. In this view, modern humans didn’t emerge from one pristine branch, but from repeated cycles of separation and reconnection among diverse African populations.
The Oldest Detectable Human Population Split: 120,000–135,000 Years Ago
The earliest population divergence still traceable in modern DNA occurred around 120,000 to 135,000 years ago. Crucially, these groups didn’t stay isolated—ongoing migration kept genes exchanging.
A pivotal dataset came from 44 Nama individuals in southern Africa. These Indigenous people are invaluable because their DNA preserves ancient signals from deep human history, as they exhibit higher genetic diversity than most other contemporary groups.
Whole-genome analysis enabled detection of subtle patterns, shedding light on ancient movements and divergences across Africa central to human origins.
What Seemed Like Archaic Hominin DNA May Reflect Deeper African Structure
One standout finding concerns archaic hominins—extinct human relatives. Previously, unusual genetic patterns in African DNA were attributed to interbreeding with these groups.
This study proposes an alternative: signals once interpreted as archaic admixture may instead reflect ancient population structure within Homo sapiens ancestors. Those differences likely existed among partly isolated but interconnected African groups—no external branch needed.
“Previous more complicated models proposed contributions from archaic hominins, but this model indicates otherwise,” said co-author Tim Weaver, UC Davis professor of anthropology.
The authors estimate 1–4% of contemporary human genetic differentiation traces to these ancient stem populations. This isn’t about profound biological separations—more a subtle, enduring imprint from our shared past.
Why African Fossils Are So Hard to Place in Human Evolution
The model also explains fossil interpretation challenges. Discovering an ancient skull in Africa sparks debate: direct ancestor, dead-end branch, or genetic contributor?
It suggests we may not need a dramatically distinct group at the base of Homo sapiens. With populations mixing across Africa for hundreds of thousands of years, they shared broad physical traits—no rigid divides.
Thus, enigmatic fossils like Homo naledi likely represent peripheral relatives, not major modern human contributors. Their genetic legacy in us? Probably negligible.
“We are presenting something that people had never even tested before,” Henn said. “This moves anthropological science significantly forward.”
