Just 1.5 per cent of our genome is ‘uniquely human’
Less than ten per cent of your genome is unique to modern humans, with the rest being shared with ancient human relatives such as Neanderthals. Researchers also found that the portion of DNA that’s unique to modern humans is enriched for genes involved with brain development and brain function. This finding suggests that genes for brain development and function are what really set us apart genetically from our ancestors. However, it’s unclear what this finding means in terms of the actual biological differences between humans and Neanderthals. “That is a giant question that future work will have to disentangle,” says Richard E. Green, an associate professor of biomolecular engineering at the University of California. “At least now we know where to look.”
Researchers aimed to tease apart the genes that are unique to modern-day humans as opposed to inherited from ancient ancestors.
But this process is tricky because humans have genetic variants they share with Neanderthals, not only because the two groups interbred, but also because humans and Neanderthals inherited some of the same genetic variants from a common ancestor.
The researchers developed an algorithm, known as the ‘speedy ancestral recombination graph estimator’, which enabled them to more efficiently tell the difference between parts of the genome modern humans inherited due to interbreeding with Neanderthals and parts that humans shared with Neanderthals prior to the evolutionary split between Neanderthals and humans roughly 500,000 years ago.
They used the algorithm to analyse 279 modern human genomes, two Neanderthal genomes and one genome from Denisovans, another group of archaic humans. They found that just one-and-a-half to seven per cent of the human genome is unique to Homo sapiens, free from signs of interbreeding or ancestral variants. Green described the seven per cent value as the portion of the human genome where humans are more closely related to each other than to Neanderthals or Denisovans. The 1.5 per cent value is the portion that includes gene variants that all humans have, but no Neanderthal or Denisovan had.
“It seems like not a lot of the genome is uniquely human,” Green said. Researchers were also surprised that most of the genes within that portion were “genes that we know and recognise,” largely coding for proteins known to be involved in brain development and function rather than genetic material that isn’t known to have a specific function.