Scientists have made strides in uncovering what makes humans unique by refining how we compare modern human DNA to that of our extinct ancestors. A recent study published in Science Advances sheds light on the small yet significant portion of our genome that is uniquely human, a finding that might reshape our understanding of how we diverged from Neanderthals and Denisovans, our closest hominin relatives.
Through advanced genetic analysis, researchers discovered that only about 7% of the human genome is unique to modern humans and not shared with other early ancestors. This percentage, according to Nathan Schaefer, a computational biologist at the University of California and co-author of the study, suggests that humans may not be as genetically distinct from Neanderthals as once thought. The finding contrasts with the long-standing assumption that humans have a vast genetic divergence from other hominin species.
The research team based its analysis on DNA extracted from ancient fossils of Neanderthals and Denisovans dating back roughly 40,000 to 50,000 years, as well as from 279 modern human genomes sampled from diverse populations worldwide. These fossils offer unique insights, as they capture the genetic code of early hominins, enabling scientists to identify segments of DNA that are distinct to modern humans. However, pinpointing unique genes is challenging because modern humans share variable portions of their genome with Neanderthals, and these shared genes vary across different populations.
To address these complexities, researchers created a new computational tool that effectively accounts for gaps in the genetic sequences of ancient hominins. John Hawks, a paleoanthropologist at the University of Wisconsin-Madison, praised this tool for its utility in dealing with incomplete data, which is a common obstacle in ancient genome research. With this tool, researchers could more accurately distinguish between the genes shared across all modern humans and those shared with our ancestors, offering a clearer picture of genetic uniqueness in modern humans.
One of the study’s significant findings is that a tiny fraction of our genome—just 1.5%—is not only unique to our species but also shared among all people alive today. Scientists believe this fraction of DNA could hold critical clues about what makes us uniquely human. Richard Green, a computational biologist at the University of California, Santa Cruz, noted that this 1.5% of DNA is notably enriched with genes related to neural development and brain function. This connection suggests that our cognitive abilities, particularly those associated with higher-order brain functions, could be among the most distinctive aspects of modern human evolution.
Green, who contributed to the first Neanderthal genome sequence in 2010, has long been at the forefront of research into human genetic differences from our extinct relatives. His work and that of other scientists, such as geneticist Joshua Akey, who showed in 2014 that modern humans carry Neanderthal DNA, underscore the progress made over the last decade in understanding human ancestry. New technologies have allowed researchers to refine genetic analysis techniques, improving the accuracy with which they can compare ancient and modern DNA. This enables more nuanced questions about human history, evolution, and the traits that define our species.
Nevertheless, not all scientists fully agree with the new findings. Alan Templeton, a population geneticist at Washington University in St. Louis, challenges the study’s underlying assumption that human genome changes are randomly distributed. He suggests that genetic variations might cluster in specific hotspots, potentially affecting interpretations of what constitutes uniquely human DNA.
Despite these differing perspectives, the findings highlight humanity’s relatively recent emergence as a distinct species. The genetic overlap with Neanderthals and Denisovans serves as a reminder that we once shared the planet with other human lineages. According to Akey, this reinforces the notion that Homo sapiens is a young species in evolutionary terms, emerging at a time when multiple hominin species existed concurrently.
Ultimately, the study opens the door to a deeper understanding of what makes us human, particularly through genes associated with brain function and cognitive development. As researchers continue to develop more sophisticated tools to analyze ancient DNA, we may uncover even more detailed insights into our evolutionary journey, including the origins of complex thought, social behavior, and cultural expression that define our species. This ongoing research offers both a fascinating glimpse into our evolutionary past and a foundation for exploring potential evolutionary paths into the future.