The new findings accentuate just how often the different species interacted with each other and the impact those relationships had over the course of human history
The human species may be the only one of its kind in the world, but a new study has found that our genome may not be as unique as we originally believed.
A mere 1.5 to seven per cent of our genome is “uniquely human”, the study, published Friday in the journal Science Advances, has stated, with the rest shared with our ancient human relatives, the Neanderthals and Denisovans.
“The evolutionary family tree shows there are regions of our genome that make us uniquely human,” Richard Green, director of the paleogenomics lab at the University of California, Santa Cruz and co-author of the new study, told Business Insider. “Now we have a catalog of those, and it’s a surprisingly small fraction of the genome.”
It’s no secret that our ancestors had frequently mingled — researchers in 2013 found the first known remains of a child born to Neanderthal and human parents and in 2018, the remains of a little girl born to Neanderthal and Denisovan parents.
However, the new findings accentuate just how often the different species interacted with each other and the impact those relationships had over the course of human history.
“More or less everywhere we look, admixture is not the exception at all, but rather the rule,” Green said.
In order to track a hominin family tree, Green’s team constructed an algorithm, named the Speedy Ancestral Recombination Graph Estimator (SARGE), which tracked how our genes weaved together with that of Neanderthals and Denisovans over time.
The algorithm was passed through the genomes of 279 modern humans as well as one Denisovan and two Neanderthals.
“Using the resulting ancestral recombination graph, we map Neanderthal and Denisovan ancestry, incomplete lineage sorting, and the absence of both across modern human genomes,” the team wrote.
“We find evidence of at least one wave of Neanderthal admixture into the ancestors of all non-Africans.”
The algorithm, the study explained, distinguished which parts of the human genome have no admixture — no mixing with Neanderthals or Denisovans.
It also pointed out which genes humans inherited from an older ancestor, from 500,000 years ago or so, which eventually evolved into our species as well as that of the Neanderthals and others. This could mean that there were other human populations, as yet undiscovered, which had mixed with Neanderthals and Denisovans before they mixed with modern humans, Green posited.
The genes that are uniquely human are connected to our neural development, Green said, many of which came out during two distinct bursts of evolution, one that occurred 600,000 years ago and the other, 200,000 years ago.
“Now we know human-specific stuff has to do with brain function,” Green said.
It isn’t clear why those bursts of evolution happened when they did. But “It’s extremely tempting to speculate that one or more of these bursts had something to do the incredibly social behaviour humans have – mediated in large part by our expert control of speech and language,” Green said.