Scientists worldwide have long accepted that humans originated from a single ancestral population in Africa roughly 50,000 to 70,000 years ago and eventually spread across the globe.
But a new genetic analysis is challenging this historic theory.
The study, published in the journal Nature, compared genetic material from present-day African populations with fossil evidence from early Homo sapiens.
What the researchers found was a tangled web of interconnected branches showing that early human groups spread across Africa, separating and reconnecting over vast stretches of time. Their differences left remarkable traces that are still visible in people's DNA today.
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The research was co-led by Brenna Henn, professor of anthropology and the Genome Center at UC Davis, and Simon Gravel of McGill University.
According to Henn, the research fills the 'uncertainty' between fossils and ancient DNA.
"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."
Their team tested multiple theories about human evolution and migration across Africa by analysing genetic data from populations in southern, eastern, and western Africa.
In the study, saliva samples were collected from the Nama in their villages between 2012 and 2015, and the extracted DNA was used to produce 44 newly sequenced Nama genomes. The Nama are an Indigenous population in southern Africa known for carrying high levels of genetic diversity, making them a valuable group for tracing human ancestry.
The study shows clear patterns of diversity in modern human DNA that older, simpler frameworks could not explain, the researchers noted.
"We are presenting something that people had never even tested before," Henn explained. "This moves anthropological science significantly forward."
Co-author Tim Weaver, a UC Davis professor of anthropology who specialises in early human fossils, said the results should trigger a rethink of older explanations.
"Previous more complicated models proposed contributions from archaic hominins, but this model indicates otherwise," he said.
The model also affects how fossil records are interpreted.
According to the authors, only around one to four percent of the genetic differences seen among living human populations can be traced back to variation between these early ancestral groups.
Because those groups were mixing so extensively, they were likely quite similar in appearance. That means any ancient fossils that look dramatically different from early modern humans, such as Homo naledi, were likely separate lineages that played little to no role in the evolution of the humans alive today, the authors stated.