We carry DNA from extinct cousins like Neanderthals. Science is now revealing their genetic legacy

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Neanderthals live within us.

These ancient human cousins, and others called Denisovans, Our early Homo sapiens ancestors once lived with, They mated and had children. So some of who they were never went away – it’s in our genes. And science is beginning to reveal just how much it shapes us.

Using the new and rapidly improving ability to piece together fragments of ancient DNA, scientists are discovering that traits inherited from our ancient cousins ​​are still with us, influencing our fertility. , are also affecting our immune system. How our bodies handled the COVID-19 virus,

“Now we’re passing on the genetic legacy and learning what it means for our bodies and our health,” said Mary Prendergast, an archaeologist at Rice University.

In just the past few months, researchers have linked Neanderthal DNA to a serious hand disease, shape of people’s nose And various other human traits, they even inserted a gene It was taken into rats by Neanderthals and Denisovans to investigate its effects on biology, and found that it gave them larger heads and an extra rib.

Much of human travel remains a mystery. But Dr. Hugo Zeberg of the Karolinska Institutet in Sweden said new technologies, research and collaborations are helping scientists answer basic but timeless questions: “Who are we? Where did we come from?”

And the answers point to a deeper reality: There are more similarities between our extinct cousins ​​than we thought.

Neanderthal within us

Until recently, the genetic heritage of ancient humans was invisible because scientists were limited to dissecting bones only by their shape and size. But there has been a steady stream of discoveries from ancient DNA, an area of ​​study Nobel laureate Svante Pääbo Who first pieced together the Neanderthal genome.

Advances in finding and interpreting ancient DNA have allowed them to look at things like genetic changes over time to better adapt to the environment or through random chance.

It is also possible to find out how much genetic material people in different regions bring from ancient relatives that met our predecessors.

Research shows that some African populations have almost no Neanderthal DNA, compared to 1% to 2% in those with European or Asian backgrounds. Denisovan DNA is barely detectable in most parts of the world, but makes up 4% to 6% of the DNA of people in Melanesia, which stretches from New Guinea to the Fiji Islands.

It may not seem like much, but it adds up. “Half of the Neanderthal genome is still in small fragments scattered around modern humans,” said Zeberg, who has closely collaborated with Pääbo.

It’s also enough to affect us in real ways. Scientists don’t know completely yet, but they are learning that it can be both helpful and harmful.

For example, Neanderthal DNA has been linked to auto-immune diseases such as Graves’ disease and rheumatoid arthritis. When Homo sapiens came out of Africa, they had no immunity to the diseases in Europe and Asia, but Neanderthals and Denisovans already lived there.

“By breeding with them, we got a quick improvement in our immune systems, which was good news 50,000 years ago,” said human evolution researcher Chris Stringer of the Natural History Museum in London. “The result today is that for some people, our immune systems are overly sensitive, and sometimes they themselves become victims of it.”

Similarly, Rick Potts, director of the Human Origins Program at the Smithsonian Institution, said a gene related to blood clotting, which is believed to have come from Neanderthals in Eurasia, was helpful in the “rugged world of the Pleistocene.” Must have been. But today it may increase the risk of stroke for older adults. “For every benefit,” he said, “growth has costs.”

In 2020, Research by Zeberg and Pääbo A major genetic risk factor for severe COVID-19 was found to be inherited from Neanderthals. “We compared it to the Neanderthal genome and it was a perfect match,” Zeberg said. “I kind of fell out of my chair.”

Next year, he found A set of DNA variants along a single chromosome inherited from Neanderthals had the opposite effect: protecting people from severe COVID.

The list goes on: Research has linked Neanderthal genetic variants to skin and hair color, behavioral symptoms, skull shape And diabetes type 2, One Study found that people who felt more pain than others were more likely to have Neanderthal pain receptors. one more found that one-third of women in Europe had inherited the Neanderthal receptor for the hormone progesterone, which is linked to increased fertility and fewer miscarriages.

Little is known about our genetic heritage from the Denisovans – although some research has linked genes derived from them to fat metabolism and Better adaptation to high altitude, Manasa Raghavan, a human genetics expert at the University of Chicago, said a portion of Denisovan DNA has been found in Tibetans, who are still living and thriving in low-oxygen environments today.

Scientists have also found evidence of “ghost populations” within the genetic code of modern humans – groups whose fossils have not yet been discovered.

So why do we survive?

In the past, the story of the survival of modern humans was “always told as a success story, almost like a hero’s story”, in which Homo sapiens rose above the rest of the natural world and overcame the “shortcomings” of their cousins. But got under control. Said.

“Well, that’s not quite the right story.”

By the time Homo sapiens left Africa, Neanderthals and Denisovans had existed for thousands of years. Scientists used to think that we won because we had more complex behavior and better technology. But recent research shows that Neanderthals talked, cooked with fire, made art objects, had sophisticated tools and hunting behavior, and even wore makeup and jewelry.

Many theories now link our existence to our ability to travel far and wide.

“We spread all over the world, much more than these other variants,” Zeberg said.

While Neanderthals were specifically adapted to cold climates, Potts said, Homo sapiens was able to spread into all different types of climates after emerging in tropical Africa. “We are very adaptable, culturally adaptable, to many places in the world,” he said.

Meanwhile, Neanderthals and Denisovans faced harsher conditions in the north, such as frequent ice ages and ice sheets, which likely trapped them in small areas, said archaeologist Eleanor Scerri of the Max Planck Institute for Geoanthropology in Germany. . They lived in smaller populations with greater risk of genetic collapse.

Plus, we had agile, efficient bodies, Prendergast said. It took a lot more calories to feed the burly Neanderthals than the comparatively slimmer Homo sapiens, so Neanderthals had more trouble living and moving around, especially when food became scarce.

Janet Young, curator of physical anthropology at the Canadian Museum of History, pointed to another interesting hypothesis – shared by anthropologist Pat Shipman in one of her books – that dogs may have played a larger role in our survival. Researchers found skulls of domesticated dogs at Homo sapiens sites much earlier than anyone had found before. Scientists believe that dogs have made hunting easier.

About 30,000 years ago, all other hominins on Earth were wiped out, leaving Homo sapiens as the last humans left.

‘Conversate and mix’

Still, every new scientific revelation points to how much we owe our ancient cousins.

John Hawkes, a paleontologist at the University of Wisconsin–Madison, said human evolution was not about “survival of the fittest and extinction.” It’s all about “interacting and mixing”.

Researchers hope to learn more as science continues to advance, allowing them to extract information from the smallest traces of ancient life. Even when fossils aren’t available, scientists can still do this today Obtain DNA from Soil and Sediment Where ancient humans once lived.

And there are less explored places in the world where they hope to learn more. Zeberg said “biobanks” that collect biological samples will likely be established in more countries.

As they delve deeper into humanity’s genetic heritage, scientists hope to find even more evidence of how much we mingled with our ancient cousins ​​and what they left us with.

“Maybe,” Zeberg said, “we shouldn’t see them so different.”

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This story was first published in September. 25, 2023. It was updated in September. 27, 2023 to remove the estimated number of Neanderthals, which was erroneously reported as 100,000. Most scientists believe it was much higher than 100,000.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. AP is solely responsible for all content.



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