2023-09-25 05:53:05
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—was the only true humans to have walked the Earth. Previous forms, such as Neanderthals, were thought to have been only a step along the path of evolution, and had disappeared because we were a better version.
Now that image is changing.
In recent years, researchers have gained the ability to remove DNA from ancient hominids, including our ancestors and other bipedal relatives. The technology to obtain ancient DNA has revolutionized the way we study human history and has taken off rapidly, with a steady stream of studies exploring the genes of people who inhabited the planet long ago.
Along with more fossils and artifacts, the DNA findings are making us grasp a challenging idea: We’re not that special. For most of human history we shared the Earth with other classes of early humans, and those now-extinct groups were very much like us.
“We can see that they were fully human. But, interestingly, a different kind of human,” said Chris Stringer, an expert in human evolution at the Natural History Museum in London. “A different kind of human.”
What’s more, humans had close—and even intimate—interaction with some of these other groups, including Neanderthals, Denisovans, and “ghost populations” we only know from DNA.
“(The current) is a unique time in human history, in which only one of us exists,” Stringer said.
Scientists now know that after Homo sapiens appeared in Africa about 300,000 years ago, it overlapped with a whole host of other hominids, explained Rick Potts, director of the Smithsonian Institution’s Program on the Origin of Humans.
Neanderthals were in Europe. Homo heidelbergensis and Homo naledi lived in Africa. Homo floresiensis, sometimes called the hobbit because of its short stature, lived in Indonesia, while the long-legged Homo erectus was found in Asia.
Scientists began to realize that all of these hominids were not our direct ancestors. They were more like our cousins: lineages that separated from a common source and headed in different directions.
Archaeological finds have shown that some of them had complex behaviors. Neanderthals painted cave walls, Homo heidelbergensis hunted large animals like rhinos and hippos, and some scientists believe that even Homo naledi — which had a small brain — buried its dead in South African cave systems. A study last week found that early humans were already building structures with wood before Homo sapiens evolved.
The researchers also wondered: If these other classes of human beings were not so different from Homo sapiens, did our ancestors have sexual relations with them?
For some, the mix was difficult to imagine. Many argued that as Homo sapiens ventured out of Africa, they replaced other groups without mating with them. Archaeologist John Shea of Stony Brook University in New York said he used to think that Neanderthals and Homo sapiens were rivals, and believed that “if they ran into each other, they would probably kill each other.”
But DNA has revealed that there were other interactions, which changed who we are today.
In 2010, Swedish geneticist Svante Paabo and his team put together a complicated puzzle. They were able to assemble fragments of ancient DNA into a complete Neanderthal genome, a feat long thought impossible and for which Paabo won a Nobel Prize last year.
This ability to read ancient DNA revolutionized the field, and it is constantly being improved.
For example, when scientists applied these techniques to a pinky finger bone and some huge molars found in a cave in Siberia, they found genes that didn’t match anything they had 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 hominid, now known as Denisovans: the first cousins of humans identified only from their DNA.
Armed with these genomes from Neanderthals and Denisovans, scientists could compare them with modern people and look for pieces of DNA that matched. When they found them, they found clear signs of a mixture.
DNA evidence showed that Homo sapiens mated with groups including Neanderthals and Denisovans. It even revealed evidence of other “ghost populations,” groups that are part of our genetic code, but whose fossils we have not yet found.
It is difficult to pinpoint exactly when and where these interactions occurred. Apparently our ancestors mixed with Neanderthals shortly after leaving Africa and heading towards Europe. They probably encountered the Denisovans in parts of East and Southeast Asia.
“They didn’t have a map, they didn’t know where they were going,” said the Smithsonian’s Potts. “But as they went up the next hill and into the next valley, they encountered populations of people who looked a little different than them, but they mated, they exchanged genes.”
So, even though Neanderthals did look different from Homo sapiens — from their larger nose to their shorter limbs — it was insufficient to create a “wall” between the groups, Shea said.
“They probably thought, ‘Oh, these people look a little different,’” he added. “’The color of his skin is a little different. Their faces look a little different. But they are good people, we are going to try to talk to them.’”
The idea that modern humans, and especially 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.
A painting of a Neanderthal, created to reflect the views of a eugenics supporter, has made its way into textbooks and museums for decades.
The new findings have completely upended the idea that older, more ape-like creatures began walking more upright and becoming more complex until they reached their full form in Homo sapiens, Young said. Along with genetic evidence, other archaeological findings have shown that Neanderthals had complex behaviors around hunting, cooking, using tools, and even creating art.
Still, even though we now know that our ancient human cousins were like us—and are part of who we are now—the idea of ape-like cavemen has been difficult to shake.
Artist John Gurche is trying. He specializes in creating life-size models of ancient humans for museums, including the Smithsonian and the American Museum of Natural History, in hopes of helping public perception catch up with scientific findings.
Skulls and sculptures looked out from the shelves of his studio this year as he worked on a Neanderthal head, pushing bits of hair into the silicone skin.
Bringing the new way of seeing things to the public has not been easy, Gurche noted: “This image of the caveman is very persistent.”
For him, having the correct scientific basis is crucial. He has worked on dissections of humans and apes to understand their anatomy, but he also hopes to bring out emotions in his performances.
“These were once living, breathing individuals. And they felt sadness and joy and pain,” Gurche said. “They’re not in some fairyland; They are not some fantastic creatures. “They were alive.”
Scientists can’t get useful genetic information from every fossil they find, especially if it’s really old or in an unfavorable climate. They haven’t been able to gather much ancient DNA from Africa, where Homo sapiens first evolved, because it has degraded due to heat and humidity.
Still, many hope that as DNA technology continues to advance, we will be able to go even further into the past and obtain ancient genomes from more parts of the world, adding more touches to our picture of human history.
Because, even though we were the only ones to survive, the other extinct groups played a crucial role in our history, and in our present. They are part of a common humanity that connects every person, said Mary Prendergast, an archaeologist at Rice University.
“If you look at the fossil record, the archaeological record, the genetic record,” he said, “you will see that we have much more in common than what divides us.”
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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Scientific and Educational Media Group. The AP is solely responsible for all content.
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