Scientists have made a surprising discovery about our ancient past: modern humans didn’t come from just one ancestral group, but from at least two different populations that split apart long ago and later came back together.
A research team from the University of Cambridge found that these two ancient groups separated about 1.5 million years ago.
Then, around 300,000 years ago—long before humans began to spread across the world—they mixed again.
One group ended up contributing about 80% of the DNA found in modern humans, while the other group contributed about 20%.
For many years, scientists believed that Homo sapiens (modern humans) evolved from a single group in Africa between 200,000 and 300,000 years ago.
But this new study, published in Nature Genetics, shows that our story is more complex.
“Our research shows that humans came from two separate groups that lived apart for more than a million years,” said Dr. Trevor Cousins, the study’s lead author. “Then they reunited and gave rise to the modern human species.”
Previous studies had already shown that humans interbred with other human relatives, like Neanderthals and Denisovans, around 50,000 years ago. But this newly discovered mixing event happened much earlier—and had a much bigger impact on our genes.
Instead of using ancient bones or fossils, the team studied DNA from modern people all over the world using data from the 1000 Genomes Project. They developed a computer model called cobraa to track how ancient populations may have split and merged over time.
The study also revealed that one of the two ancient groups went through a tough time right after the split, shrinking to a very small size before slowly growing again over a million years. This group is believed to be the ancestor not only of modern humans but also of Neanderthals and Denisovans.
Interestingly, the smaller portion of DNA from the second group may have played an important role in human evolution—especially in brain development and processing.
Some of the genes from this group ended up far from important areas of the genome, possibly because they weren’t fully compatible with the majority group. Over time, natural selection may have removed some of these less useful or harmful genes.
The team also tested their method on other animals like bats, dolphins, chimpanzees, and gorillas, and found that mixing between ancient groups is common in nature.
“Our history isn’t a simple straight line,” said Cousins. “Human evolution—and the evolution of many animals—is full of twists, turns, and mixing.”
As research continues, scientists hope to learn even more about these mysterious ancestors and how they helped shape who we are today.
