Genetic tools have enabled scientists to assess the evolution of humans through DNA, and researchers have shown that modern people still carry remnants from other ancient hominid species like Denisovans and Neanderthals. We also know that our genome has a high degree of similarity with chimpanzees and bonobos, species that have an ancestor in common with us. It seems that only small biological changes, like a big brain, have made us human. Now, a study reported in Science Advances has shown that only 1.5 to 7 percent of the human genome is common to other modern humans, and not found in our early ancestors.
“That’s a pretty small percentage,” said study co-author Nathan Schaefer, a University of California computational biologist. “This kind of finding is why scientists are turning away from thinking that we humans are so vastly different from Neanderthals.”
We've already determined that modern humans carry Neanderthal DNA, but different people carry different parts of the Neanderthal genome in different places in their DNA. This work utilized data from DNA carried in fossils of Neanderthals and Denisovans that lived roughly 45,000 years ago, and compared it to DNA from 279 humans from around the world living in current times. This work aimed to find which genes are only present in modern humans.
The researchers had to create a statistical tool that could account for missing data in ancient DNA. The work suggested that as little as 1.5 percent of the modern human genome may unique to us, but common to everyone now living; that percentage may also be a bit higher - as much as 7 percent, they noted. This little bit of DNA may be at the root of what it is to be human, and unsurprisingly, a lot of it has to do with our brains.
“We can tell those regions of the genome are highly enriched for genes that have to do with neural development and brain function,” said study co-author Richard Green, a University of California, Santa Cruz computational biologist.
The study also suggested that the genomic changes that gave rise to our species happened in several "bursts of adaptive changes."