These ancient human cousins and others called Denisovans once lived alongside our early Homo sapiens ancestors. They mixed and had children. A part of their identity has therefore never disappeared – it is anchored in our genes. And science is beginning to reveal how much these genes shape us.
With the new and rapidly improving ability to piece together fragments of ancient DNA, scientists are discovering that traits we inherited from our ancient cousins are still present within us, influencing our fertility, immune system, and even manner How our body reacted to the COVID-19 virus.
“We now carry a genetic inheritance and are learning what that means for our bodies and our health,” said Mary Prendergast, an archaeologist at Rice University.
Just in the last few months, researchers have linked Neanderthal DNA to severe hand diseases, nose shape and various other human characteristics. They even inserted a gene carried by Neanderthals and Denisovans into mice to study its effects on biology and found that it gave them larger heads and an extra rib.
Much of man’s journey remains a mystery. But Dr. Hugo Zeberg of the Karolinska Institute in Sweden explained that new technologies, research and collaborations are helping scientists answer fundamental but cosmic questions: “Who are we? Where do we come from?”
The answers reveal a profound reality: We have much more in common with our lost cousins than we ever imagined.
The Neanderthal in us
Until recently, ancient people’s genetic heritage was invisible as scientists limited themselves to what they could figure out from the shape and size of bones. But discoveries about ancient DNA have multiplied, an area of research opened by Nobel laureate Svante Paabo, who was the first to reconstruct a Neanderthal genome.
Advances in the study and interpretation of ancient DNA have revealed genetic changes over time to better adapt to the environment or by chance.
It is even possible to determine how much genetic material people in different regions have from ancient relatives that our predecessors encountered.
Research shows that some African populations have virtually no Neanderthal DNA, while those of European or Asian descent have 1-2%. Denisovan DNA is barely detectable in most parts of the world, but makes up 4 to 6 percent of the DNA of people in Melanesia, which stretches from New Guinea to the Fiji Islands.
It doesn’t seem like much, but it adds up. “Half of the Neanderthal genome still exists, scattered in small pieces among modern humans,” says Mr. Zeberg, who works closely with Mr. Paabo.
It’s also enough to affect us in very real ways. Scientists don’t yet know the full extent, but they are learning that it can be both beneficial and harmful.
For example, Neanderthal DNA has been linked to autoimmune diseases such as Graves’ disease and rheumatoid arthritis. When Homo sapiens emerged from Africa, they were not immune to the diseases prevalent in Europe and Asia, whereas the Neanderthals and Denisovans already living there were immune.
“By crossing with them, we got a quick fix for our immune system, which was good news 50,000 years ago,” said Chris Stringer, a human evolution researcher at the Natural History Museum in New York. London. The result today is that in some people our immune systems are too sensitive and sometimes turn against themselves.”
Likewise, a gene linked to blood clotting, thought to have been transmitted from Neanderthals in Eurasia, may have been useful in the “harsh and turbulent world of the Pleistocene,” said Rick Potts, the director of the Human Origins Program at the Smithsonian Institution. But today, this gene may increase the risk of stroke in older people. “For every benefit there is a cost in evolution,” he said.
In 2020, research was carried out by MM. Zeberg and Paabo revealed that an important genetic risk factor for severe COVID-19 is inherited from Neanderthals. “We compared it to the Neanderthal genome and found a perfect match,” Zeberg said. I fell out of my chair.”
The following year, they discovered that a series of DNA variants along a single chromosome inherited from Neanderthals had the opposite effect: They protected people from severe forms of COVID.
The list goes on: Research has linked Neanderthal gene variants to skin and hair color, behavioral traits, skull shape, and type 2 diabetes. A study showed that people who report feeling more pain than others likely carry a Neanderthal pain receptor. Another study found that a third of women in Europe had inherited a Neanderthal receptor for the hormone progesterone, which is linked to increased fertility and fewer miscarriages.
Much less is known about the genetic heritage of Denisovans, although some research has linked their genes to fat metabolism and better adaptation to high altitudes. Maanasa Raghavan, a human genetics expert at the University of Chicago, said some Denisovan DNA has been found in Tibetans who continue to live and thrive in low-oxygen environments today.
Scientists have even found evidence of the existence of “ghost populations” – groups whose fossils have not yet been discovered – in the genetic code of modern humans.
Why did we survive?
In the past, the story of modern human survival “has always been told as a success story, almost a hero story,” in which Homo sapiens rose above the rest of the natural world and confronted the “shortcomings” of its cousins, Mr. Potts said.
“It’s just not the right story,” he stressed.
Neanderthals and Denisovans had existed for thousands of years when Homo sapiens left Africa. Scientists believed that Homo Sapiens won because of their more complex behavior and superior technology. But new research shows that Neanderthals spoke, cooked with fire, made art, had sophisticated tools and hunting habits, and even wore makeup and jewelry.
Several theories now link our survival to our ability to travel long distances.
“We spread all over the world, much more than these other forms,” Mr. Zeberg recalls.
While Neanderthals were specifically adapted to cold climates, Homo sapiens were able to spread into all sorts of climates after their emergence in tropical Africa, according to Potts. “We are so adaptable, culturally adaptable, to so many places in the world,” he said.
During this time, Neanderthals and Denisovans faced harsh conditions in the north, such as repeated ice ages and ice sheets that likely trapped them in small areas, said Eleanor Scerri, an archaeologist at the Max Planck Institute for Geoanthropology in Germany. They lived in smaller populations with a higher risk of genetic collapse.
“We also had agile and efficient committees,” added Mr. Prendergast. It takes many more calories to feed stocky Neanderthals than relatively thin Homo sapiens. Neanderthals therefore had a harder time fending for themselves and getting around, especially when food was scarce.
Janet Young, curator of physical anthropology at the Canadian Museum of History, put forward another interesting hypothesis – discussed by anthropologist Pat Shipman in one of his books – that dogs played an important role in our survival. Researchers have found skulls of domesticated dogs at Homo sapiens sites that are much older than previously discovered. Scientists believe that dogs made hunting easier.
About 30,000 years ago, all other hominin species on Earth had disappeared and Homo sapiens was the last survivor.
Interaction and mixing
Yet each new scientific revelation shows how much we owe to our ancient cousins.
According to John Hawks, a paleoanthropologist at the University of Wisconsin at Madison, human evolution is not about “survival of the fittest and extinction.” Rather, it is about “interaction and mixing”.
Researchers expect that as science advances, they will be able to learn more and glean information from ever-finer traces of ancient life. Even without fossils, scientists can now collect DNA from the soil and sediments where archaic humans lived.
And there are less explored places in the world that they hope to learn more about. “Biobanks” that collect biological samples are likely to emerge in other countries, said Zeberg.
As they delve deeper into humanity’s genetic heritage, scientists expect to find even more evidence of the extent of interbreeding with our ancient cousins and how much they left us.
“Maybe we shouldn’t think of them as so different,” Zeberg said.