Science paints a new picture of the ancient past, when we mixed and mated with other kinds of humans

UNDATED (AP)- What does it mean to be human?

For a long time, the answer seemed clear. Our species, Homo sapiens — with our complex thoughts and deep emotions — were the only true humans to ever walk the Earth. Earlier forms, like the Neanderthals, were thought to be just steps along the path of evolution, who died out because we were better versions.

That picture is now changing.

In recent years, researchers have gained the power to pull DNA from ancient hominins, including our early ancestors and other relatives who walked on two legs. Ancient DNA technology has revolutionized the way we study human history and has quickly taken off, with a constant stream of studies exploring the genes of long-ago people.

Along with more fossils and artifacts, the DNA findings are pointing us to a challenging idea: We’re not so special. For most of human history we shared the planet with other kinds of early humans, and those now-extinct groups were a lot like us.

“We can see them as being fully human. But, interestingly, a different kind of human,” said Chris Stringer, a human evolution expert at London’s Natural History Museum. “A different way to be human.”

What’s more, humans had close — even intimate — interactions with some of these other groups, including Neanderthals, Denisovans and “ghost populations” we only know from DNA.

“It’s a unique time in human history when there are only one of us,” Stringer said.

A WORLD WITH MANY HOMININS
Scientists now know that after H. sapiens first showed up in Africa around 300,000 years ago, they overlapped with a whole cast of other hominins, explained Rick Potts, director of the Smithsonian’s Human Origins Program.

Neanderthals were hanging out in Europe. Homo heidelbergensis and Homo naledi were living in Africa. The short-statured Homo floresiensis, sometimes known as the “Hobbit,” was living in Indonesia, while the long-legged Homo erectus was loping around Asia.

Scientists started to realize all these hominins weren’t our direct ancestors. Instead, they were more like our cousins: lineages that split off from a common source and headed in different directions.

Archaeological finds have shown some of them had complex behaviors. Neanderthals painted cave walls, Homo heidelbergensis hunted large animals like rhinos and hippos, and some scientists think even the small-brained Homo naledi was burying its dead in South African cave systems. A study last week found early humans were building structures with wood before H. sapiens evolved.

Researcher also wondered: If these other kinds of humans were not so different, did our ancestors have sex with them?

For some, the mixing was hard to imagine. Many argued that as H. sapiens ventured out of Africa, they replaced other groups without mating. Archaeologist John Shea of New York’s Stony Brook University said he used to think of Neanderthals and H. sapiens as rivals, believing “if they bumped into each other, they’d probably kill each other.”

DNA REVEALS ANCIENT SECRETS
But DNA has revealed there were other interactions, ones that changed who we are today.

In 2010, the Swedish geneticist Svante Paabo and his team pieced a tricky puzzle together. They were able to assemble fragments of ancient DNA into a full Neanderthal genome, a feat that was long thought to be impossible and won Paabo a Nobel Prize last year.

This ability to read ancient DNA revolutionized the field, and it is constantly improving.

For example, when scientists applied these techniques to a pinky bone and some huge molars found in a Siberian cave, they found genes that didn’t match anything seen before, said Bence Viola, an anthropologist at the University of Toronto who was part of the research team that made the discovery. It was a new species of hominin, now known as Denisovans, who were the first human cousins identified only by their DNA.

Armed with these Neanderthal and Denisovan genomes, scientists could compare them to people today and look for chunks of DNA that match. When they did, they found clear signs of crossover.

THE NEW HUMAN STORY
The DNA evidence showed that H. sapiens mated with groups including Neanderthals and Denisovans. It even revealed evidence of other “ghost populations” — groups who are part of our genetic code, but whose fossils we haven’t found yet.

It’s hard to pin down exactly when and where these interactions happened. Our ancestors seem to have mixed with the Neanderthals soon after leaving Africa and heading into Europe. They probably bumped into the Denisovans in parts of East and Southeast Asia.

“They didn’t have a map, they didn’t know where they were going,” the Smithsonian’s Potts said. “But looking over the next hillside into the next valley, (they) ran into populations of people that looked a bit different from themselves, but mated, exchanged genes.”

So even though Neanderthals did look distinct from H. sapiens — from their bigger noses to their shorter limbs — it wasn’t enough to create a “wall” between the groups, Shea said.

“They probably thought, ‘Oh, these guys look a little bit different,’” Shea said. “‘Their skin color’s a little different. Their faces look a little different. But they’re cool guys, let’s go try to talk to them.’”

COMPLEX NEANDERTHALS
The idea that modern humans, and particularly white humans, were the pinnacle of evolution came from a time of “colonialism and elitism,” said Janet Young, curator of physical anthropology at the Canadian Museum of History.

One Neanderthal painting, created to reflect the vision of a eugenics advocate, made its way through decades of textbooks and museum displays.

The new findings have completely upended the idea that earlier, more ape-like creatures started standing up straighter and getting more complex until they reached their peak form in H. sapiens, Young said. Along with the genetic evidence, other archaeological finds have shown Neanderthals had complex behaviors around hunting, cooking, using tools and even making art.

Still, even though we now know our ancient human cousins were like us — and make up part of who we are now — the idea of ape-like cave men has been hard to dislodge.

Artist John Gurche is trying. He specializes in creating lifelike models of ancient humans for museums, including the Smithsonian and the American Museum of Natural History, in hopes of helping public perception catch up to the science.

Skulls and sculptures gazed out from the shelves of his studio earlier this year as he worked on a Neanderthal head, punching pieces of hair into the silicone skin.

Bringing the new view to the public hasn’t been easy, Gurche said: “This caveman image is very persistent.”

For Gurche, getting the science right is crucial. He has worked on dissections of humans and apes to understand their anatomy, but also hopes to bring out emotion in his portrayals.

“These were once living, breathing individuals. And they felt grief and joy and pain,” Gurche said. “They’re not in some fairyland; they’re not some fantasy creatures. They were alive.”

MANY CONNECTIONS STILL TO BE FOUND
Scientists can’t get useful genetic information out of every fossil they find, especially if it’s really old or in the wrong climate. They haven’t been able to gather much ancient DNA from Africa, where H. sapiens first evolved, because it has been degraded by heat and moisture.

Still, many are hopeful that as DNA technology keeps advancing, we’ll be able to push further into the past and get ancient genomes from more parts of the world, adding more brushstrokes to our picture of human history.

Because even though we were the only ones to survive, the other extinct groups played a key role in our history, and our present. They are part of a common humanity connecting every person, said Mary Prendergast, a Rice University archeologist.

“If you look at the fossil record, the archeological record, the genetic record,” she said, “you see that we share far more in common than what divides us.”

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SEPTEMBER 25, 2023:

UNDATED (AP)- More research is showing that we carry genes from other kinds of ancient humans, and their DNA affects our lives today. DNA research has found that our Homo sapiens ancestors mated with Neanderthals and Denisovans long ago. We were the only ones to survive, which may have to do with how our ancestors were able to adapt to many parts of the world. But we still carry these other groups in our genes. And a growing body of science is uncovering how their DNA affects us today. Neanderthal genes have been linked with our immune systems and COVID-19 response, while Denisovan genes may help adapt to high altitudes.

UNDATED (AP)- Neanderthals live on within us.

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

Using the new and rapidly improving ability to piece together fragments of ancient DNA, scientists are finding that traits inherited from our ancient cousins are still with us now, affecting our fertility, our immune systems, even how our bodies handled the COVID-19 virus.

“We’re now carrying the genetic legacies and learning about what that means for our bodies and our health,” said Mary Prendergast, a Rice University archeologist.

In the past few months alone, researchers have linked Neanderthal DNA to a serious hand disease, the shape of people’s noses and various other human traits. They even inserted a gene carried by Neanderthals and Denisovans into mice to investigate its effects on biology, and found it gave them larger heads and an extra rib.

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

And the answers point to a profound reality: We have far more in common with our extinct cousins than we ever thought.

NEANDERTHALS WITHIN US
Until recently, the genetic legacy from ancient humans was invisible because scientists were limited to what they could glean from the shape and size of bones. But there has been a steady stream of discoveries from ancient DNA, an area of study pioneered by Nobel Prize winner Svante Paabo who first pieced together a Neanderthal genome.

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

It’s even possible to figure out how much genetic material people from different regions carry from the ancient relatives our predecessors encountered.

Research shows some African populations have almost no Neanderthal DNA, while those from European or Asian backgrounds have 1% to 2%. 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 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 collaborates closely with Paabo.

It’s also enough to affect us in very real ways. Scientists don’t yet know the full extent, but they’re learning it can be both helpful and harmful.

For example, Neanderthal DNA has been linked to auto-immune 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.

“By interbreeding with them, we got a quick fix to our immune systems, which was good news 50,000 years ago,” said Chris Stringer, a human evolution researcher at the Natural History Museum in London. “The result today is, for some people, that our immune systems are oversensitive, and sometimes they turn on themselves.”

Similarly, a gene associated with blood clotting believed to be passed down from Neanderthals in Eurasia may have been helpful in the “rough and tumble world of the Pleistocene,” said Rick Potts, director of the human origins program at the Smithsonian Institution. But today it can raise the risk of stroke for older adults. “For every benefit,” he said, “there are costs in evolution.”

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

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.

The list goes on: Research has linked Neanderthal genetic variants to skin and hair color, behavioral traits, skull shape and Type 2 diabetes. One study found that people who report feeling more pain than others are likely to carry a Neanderthal pain receptor. Another found that a third of women in Europe inherited a Neanderthal receptor for the hormone progesterone, which is associated with increased fertility and fewer miscarriages.

Much less is known about our genetic legacy from Denisovans – although some research has linked genes from them to fat metabolism and better adaptation to high altitudes. Maanasa Raghavan, a human genetics expert at the University of Chicago, said a stretch of Denisovan DNA has been found in Tibetans, who continue to live and thrive in low-oxygen environments today.

Scientists have even found evidence of “ghost populations” — groups whose fossils have yet to be discovered — within modern humans’ genetic code.

SO WHY DID WE SURVIVE?
In the past, the tale of modern humans’ survival “was always told as some success story, almost like a hero’s story,” in which Homo sapiens rose above the rest of the natural world and overcame the “insufficiencies” of their cousins, Potts said.

“Well, that simply is just not the correct story.”

Neanderthals and Denisovans had already existed for thousands of years by the time Homo sapiens left Africa. Scientists used to think we won out because we had more complex behavior and superior 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.

Several theories now tie our survival to our ability to travel far and wide.

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

While Neanderthals were specially adapted to cold climates, Potts said, Homo sapiens were able to disperse to all different kinds of climates after emerging in tropical Africa. “We are so adaptable, culturally adaptable, to so many places in the world,” he said.

Meanwhile, Neanderthals and Denisovans faced harsh conditions in the north, like repeated ice ages and ice sheets that likely trapped them in small areas, said Eleanor Scerri, an archeologist at Germany’s Max Planck Institute for Geoanthropology. They lived in smaller populations with a greater risk of genetic collapse.

Plus, we had nimble, efficient bodies, Prendergast said. It takes a lot more calories to feed stocky Neanderthals than comparatively skinny Homo sapiens, so Neanderthals had more trouble getting by, and moving around, especially when food got scarce.

Janet Young, curator of physical anthropology at the Canadian Museum of History, pointed to another intriguing hypothesis – which anthropologist Pat Shipman shared in one of her books –- that dogs played a big part in our survival. Researchers found the skulls of domesticated dogs in Homo sapiens sites much further back in time than anyone had found before. Scientists believe dogs made hunting easier.

By around 30,000 years ago, all the other kinds of hominins on Earth had died off, leaving Homo sapiens as the last humans standing.

‘INTERACTION AND MIXTURE’
Still, every new scientific revelation points to how much we owe our ancient cousins.

Human evolution was not about “survival of the fittest and extinction,” said John Hawks, a paleoanthropologist at the University of Wisconsin-Madison. It’s about “interaction and mixture.”

Researchers expect to learn more as science continues to advance, allowing them to extract information from ever-tinier traces of ancient lives. Even when fossils aren’t available, scientists today can capture DNA from soil and sediment where archaic 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 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.”