A New Chapter in Human Origins: Africa’s Complex Family Tree
Groundbreaking genetic research has upended a long-held model of human evolution, revealing that modern humans emerged from a deeply interconnected network of populations across Africa, rather than a single ancestral group.
"This new research changes the origin of species."
— Brenna Henn, UC Davis
The Study: Challenging a Single Origin
Published in Nature in 2023, the study analyzed genetic data from present-day African populations and compared it with fossil evidence. The findings challenge the earlier 'single ancestral population' model, proposing instead a network of interconnected early human groups across Africa.
Key Results
- The earliest detectable population split among modern humans occurred roughly 120,000 to 135,000 years ago.
- Before that split, two or more weakly differentiated Homo populations had been exchanging genes for hundreds of thousands of years.
- Gene flow continued between groups even after the split.
Methods and Data Collection
The study was co-led by Brenna Henn (UC Davis) and Simon Gravel (McGill University). It included genome data from southern, eastern, and western Africa.
A crucial component was 44 newly sequenced genomes from modern Nama individuals in southern Africa, collected between 2012 and 2015. The Nama are an Indigenous population known for their high genetic diversity.
Implications for Human Evolution
The findings reshape our understanding of where we come from:
- According to the authors, 1 to 4% of genetic differentiation among living human populations can be traced to variation between ancestral stem populations.
- Fossils with very different physical traits (e.g., Homo naledi) are unlikely to represent lineages that directly contributed to Homo sapiens evolution.
- The model suggests the roots of modern humans were geographically and genetically widespread, with movement, contact, and mixing across Africa.
"Previous more complicated models proposed contributions from archaic hominins, but this model indicates otherwise."
— Tim Weaver, co-author
Subsequent Research (2024)
Two recent studies continue to build on these findings:
- A 2024 study in Nature Ecology & Evolution reported 9,000 years of genetic continuity in southernmost Africa.
- Another Nature study analyzed genomes from 28 ancient southern African individuals, finding genetic variation outside the range of living people and identifying Homo sapiens-specific variants.
Research Team
The study was co-led by:
- Brenna Henn (UC Davis)
- Simon Gravel (McGill University)
Additional co-authors include:
- Aaron Ragsdale (University of Wisconsin, Madison)
- Elizabeth Atkinson (Baylor College of Medicine)
- Eileen Hoal and Marlo Möller (Stellenbosch University, South Africa)
"This uncertainty is due to limited fossil and ancient genomic data..."
— Brenna Henn