A new study published in Nature Genetics introduces a novel coalescence-based hidden Markov model, cobraa, offering new insights into human evolutionary history. Cousins et al. (2025) analyzed genomes from the 1000 Genomes Project and the Human Genome Diversity Project to track ancient population changes.
Their results suggest that modern humans descend from two populations that split around 1.5 million years ago. These groups stayed apart for over a million years before mixing again about 300,000 years ago. After this, one group contributed around 80% of our genetic ancestry, while the other contributed about 20%.
The larger ancestral group went through a significant bottleneck early on, while the smaller group remained more stable. When these groups mixed, the genetic contributions from the minority population ended up mostly in non-coding regions of the genome, suggesting that natural selection may have reduced their presence in more biologically important regions.
The study also found that DNA from the majority ancestral group is more similar to Neanderthal and Denisovan genomes. This supports the idea that Neanderthals, Denisovans, and modern humans share deep ancestral ties.
This study challenges simplified models of human origins that focus solely on recent African bottlenecks and out-of-Africa dispersals. Instead, they point to a long and complex history of divergence and mixing within Africa, long before modern humans appeared. Expanding genomic datasets will allow methods like cobraa to reveal deeper layers of human evolutionary history.