A groundbreaking study published in Nature has unveiled a new model of human evolution, overturning the long-held notion that a single African population gave rise to all humans. Researchers have shed light on the complex story of human origins by examining the genetic material of present-day African populations and comparing it with fossil evidence of early Homo sapiens in Africa.

While it has been widely accepted that Homo sapiens originated in Africa, the specific branches of human evolution and the migration patterns across the continent have remained uncertain. The research, led by Brenna Henn from UC Davis and Simon Gravel from McGill University, aimed to address these questions by integrating genomic data from southern, eastern, and western Africa.

To expand the dataset, the team included newly sequenced genomes from 44 individuals of the Nama population in southern Africa. The Nama people are known for carrying exceptional levels of genetic diversity compared to other modern groups. Genetic data were collected from saliva samples from individuals in their villages between 2012 and 2015.

The study’s results suggest that the earliest detectable population split among early humans occurred around 120,000 to 135,000 years ago. This split happened after multiple weakly differentiated Homo populations interbreeding for hundreds of thousands of years. Even after the split, people migrated between these populations, resulting in a loosely structured human genealogy. The new model provides a more accurate explanation for the genetic variation observed among individuals and human groups than previous models.

Tim Weaver, an anthropology professor at UC Davis and co-author of the study, suggests that the research challenges previous models that proposed contributions from archaic hominins. The findings indicate that archaic hominins likely did not contribute significantly to the evolution of Homo sapiens, contrary to previous theories.

The study also has implications for interpreting the fossil record. According to the new model, morphologically divergent hominid fossils, such as Homo naledi, are unlikely to represent branches that contributed to the evolution of Homo sapiens. The authors suggest that the migration between branches resulted in morphologically similar lineages, leading to a more coherent understanding of human evolution.

The researchers predict that 1-4% of genetic differentiation among contemporary human populations can be attributed to variation in the ancestral populations. This finding challenges the idea of a single African population as the sole ancestor of all humans, highlighting the diverse origins of our species.

References

• Nikos-Rose, K. M. (2023, May 17). New uc davis research using dna changes origin of human species, researchers suggest. UC Davis; UC Davis. https://www.ucdavis.edu/news/new-uc-davis-research-using-dna-changes-origin-human-species-researchers-suggest
• Ragsdale, A. P., Weaver, T. D., Atkinson, E. G., Hoal, E. G., Möller, M., Henn, B. M., & Gravel, S. (2023). A weakly structured stem for human origins in Africa. Nature, 617(7962), 755–763. https://doi.org/10.1038/s41586-023-06055-y