Photo: ZN
A genetic analysis of more than 500 modern human genomes has revealed evidence of two previously unknown extinct human populations whose DNA survives in people living today.
Researchers developed a new method for reconstructing the genealogical history of individual sections of the human genome. Unlike traditional ancient-DNA research, the approach does not require DNA extracted from fossil remains. Instead, it identifies traces of long-extinct populations directly within the genomes of modern humans.
The study confirmed that modern humans carry genetic contributions from several ancient human groups, including Neanderthals and Denisovans. But the researchers also identified two previously unknown "ghost" lineages.
One ancient population contributed DNA to all modern humans
The first population appears to have interbred with the ancestors of modern humans in Africa more than 50,000 years ago, before the major migration of Homo sapiens out of Africa.
Researchers estimate that DNA from this population accounts for roughly 0.5% to 1% of the modern human genome. The group appears to have split from the lineage leading to modern humans, Neanderthals and Denisovans around 800,000 years ago.
One possible candidate is Homo heidelbergensis, an extinct human species that lived in Africa and Europe hundreds of thousands of years ago. However, researchers emphasize that there is currently not enough evidence to confirm this identification.
Possible traces of an even older human lineage
The study also found tiny fragments of extremely ancient DNA in people from Oceania. This lineage diverged from the ancestors of modern humans around 1.8 million years ago — long before the common ancestor of modern humans, Neanderthals and Denisovans.
The genetic contribution is extremely small, averaging around 0.002% of the analyzed genomes. However, the DNA fragments were found within regions inherited from Denisovans.
This suggests that the ancient population may have first interbred with Denisovans, whose descendants later passed some of that genetic material to modern humans.
One possible source could be Homo erectus, an ancient human species that lived across parts of Africa and Asia for an exceptionally long period. However, scientists stress that this connection remains hypothetical because very little genetic material from Homo erectus has survived.
Human evolution was more complex than a simple family tree
The findings support the growing view that human evolution was not a simple process in which populations split and developed separately. Instead, ancient human groups repeatedly migrated, interacted and exchanged genes.
Some of the inherited DNA fragments are concentrated in regions associated with the immune system and metabolism. This could indicate that genetic material acquired through ancient interbreeding sometimes provided useful adaptations, potentially helping early humans cope with new diseases, environments and food sources.
Researchers now plan to use the same method to search for additional "ghost" populations, particularly in Africa and South Asia, where ancient DNA is often poorly preserved.
The study could also help scientists investigate the evolutionary history of other species whose fossil DNA is unavailable, offering a new way to reconstruct the hidden genetic history of life on Earth.
