Scientists at the University of Cambridge have uncovered a hidden chapter in human evolution, revealing that modern humans descend from the interbreeding of two now-extinct species around 300,000 years ago. This discovery challenges the long-held belief that Homo sapiens emerged from a single lineage in Africa.
The study, published in Nature Genetics, suggests that roughly 1.5 million years ago, our ancestors split into two distinct species—similar to the divergence of chimpanzees and bonobos. After being separated for about 1.2 million years, the two populations reunited and interbred, leading to the genetic makeup we see today. According to the research, approximately 80% of modern human DNA originates from a group that had dwindled to as few as 1,000 individuals before recovering. The remaining genetic contribution, while smaller, includes genes linked to brain function, potentially influencing human cognitive evolution.
Dr. Aylwyn Scally, a geneticist from Cambridge, noted that the discovery highlights a severe bottleneck in one of the ancestral populations, which suggests a small, isolated group later played a crucial role in shaping our genetic heritage. Dr. Trevor Cousins, who led the study, added that the findings illustrate the complexity of human ancestry, emphasizing that species do not evolve in neat, separate lineages but often exchange genetic material.
While the identities of these ancient species remain uncertain, fossils from the era suggest Homo erectus and Homo heidelbergensis as possible candidates. Previous research has shown that Neanderthals and Denisovans interbred with Homo sapiens around 50,000 years ago, leaving traces in the genomes of modern non-African populations. However, this new evidence suggests that an even more significant interbreeding event occurred much earlier, shaping the genetic foundation of all living humans.
The Cambridge team used computational analysis of modern DNA, drawing on data from the 1,000 Genomes Project, which maps genetic sequences from populations worldwide. Their work, reported by The Times UK, reinforces the idea that genetic mixing has played a crucial role in human evolution—challenging the simplistic notion of species developing in isolation. As researchers continue to uncover these hidden chapters of our past, it becomes increasingly clear that our ancestry is more complex and intertwined than previously thought.
