01 October 2023
Neanderthals live on within us.
These ancient human relatives, and others, called Denisovans, once lived alongside our early Homo sapiens ancestors. The groups mixed and had children. As a result, some of the Neanderthals and Denisovans live on in our genes. And science is starting to show just how much that shapes us.
Mary Prendergast, a Rice University archeologist, said, "We're now carrying the genetic legacies and learning about what that means for our bodies and our health."
In the past few months, researchers have linked Neanderthal DNA to a serious hand disease, the shape of people's noses and other human traits. They even placed a gene carried by Neanderthals and Denisovans into mice to investigate its effects on biology. The researchers found that the gene gave the mice larger heads and an extra rib.
Much of the human story remains a mystery. But Dr. Hugo Zeberg of the Karolinska Institute in Sweden said new technologies and research are helping scientists begin to answer the questions: "Who are we? Where did we come from?"
And the answers point to a deep reality: We have far more in common with our ancient cousins than we ever thought.
Neanderthal, Denisovan DNA
Until recently, the genetic legacy from ancient humans was invisible. But there has been a number of discoveries from ancient DNA, an area of study developed by Nobel Prize winner Svante Paabo. He was first in creating a Neanderthal genome.
Research shows some African populations have almost no Neanderthal DNA, while those from European or Asian backgrounds have up to two percent. Denisovan DNA is rarely found in most parts of the world but makes up four to six percent of the DNA of people in Melanesia. The Pacific Ocean area extends from New Guinea to the Fiji Islands.
That may not sound like much, but it adds up: Even though only 100,000 Neanderthals ever lived, "half of the Neanderthal genome is still around, in small pieces scattered around modern humans," said Zeberg, who works closely with Paabo.
It is also enough to affect us in very real ways. Scientists studying the subject say the DNA can be both helpful and harmful.
For example, Neanderthal DNA has been linked to autoimmune diseases like Graves' disease and rheumatoid arthritis. When Homo sapiens came out of Africa, they had no immunity to diseases in Europe and Asia. But, Neanderthals and Denisovans already living there did.
Chris Stringer is a human evolution researcher at the Natural History Museum in London. Stringer said that by mating with Neanderthals and Denisovans, Homo sapiens "got a quick fix to our immune systems, which was good news 50,000 years ago." Stringer added, "The result today is, for some people, that our immune systems are oversensitive, and sometimes they turn on themselves."
In 2020, research by Zeberg and Paabo found that a major genetic risk factor for severe COVID-19 came from Neanderthals. "We compared it to the Neanderthal genome and it was a perfect match," Zeberg said.
The next year, they found a set of DNA variants along a single chromosome inherited from Neanderthals had the opposite effect: protecting people from severe COVID.
Much less is known about our genetic legacy from Denisovans – although some research has linked genes from them to fat processing and better performance at high altitudes. Maanasa Raghavan, a human genetics expert at the University of Chicago, said Tibetans carry an amount of Denisovan DNA. She noted that the population continues to live and do well in low-oxygen environments today.
Human evolution
John Hawks of the University of Wisconsin-Madison said that human evolution was not about "survival of the fittest and extinction." Instead, he suggested, it is about "interaction and mixture."
Researchers expect to learn more as the science continues to develop. Even when ancient bones are not available, scientists today can get DNA from soil where ancient humans once lived.
And there are less-explored places in the world where researchers hope to learn more. Zeberg said "biobanks" that collect biological materials will likely be established in more countries.
As researchers go deeper into humanity's genetic legacy, scientists expect to find even more evidence of how much we mixed with our ancient cousins and all they left us.
"Perhaps," Zeberg said, "we should not see them as so different."
I'm John Russell.
And I'm Anna Matteo.
Laura Ungar and Maddie Burakoff reported on this story for the Associated Press.
________________________________________________
Words in This Story
legacy – n. something that comes from someone in the past
trait – n. a quality that makes one person or thing different from another
genome – n. the complete set of genetic material present in an organism
scatter – v. to cause (things or people) to go in different directions
variant – n. something that is different in some way from others of the same kind