Neanderthals and Denisovans are some of the nearest ancestors to modern humans. These hominins were so similar to us that they even interbred with humans for thousands of years when the three overlapped in time and space in certain areas. Many people today still carry important genetic material from these cousins of ours — meaning that, in a sense, they never completely went extinct.
Nonetheless, Neanderthals disappeared from the fossil record about 40,000 years ago. Denisovan records are so rare that there really isn’t even a fossil record for these near-humans — there are only a handful of fossils confirmed to be Denisovans by DNA analysis and no complete skeleton so far.
“Unfortunately, [Denisovans] are super mysterious,” says David Gokhman, a geneticist at the Weizmann Institute of Science in Israel who studies Denisovans and Neanderthals. But fossil discoveries and DNA analysis still have given researchers a few clues about the ways the two hominins differed, as well as the characteristics they shared.
The New Kids on the Block
Neanderthals were first discovered in the 19th century in Belgium. Since then, a number of specimens have turned up across Europe, Central Asia and the Middle East. Denisovans are relatively recently discovered compared to Neanderthals. Nobody even knew they existed until a finger bone discovered in Denisova Cave was sequenced genetically.
A publication in Nature revealed the mitochondrial DNA in the bone differed enough from Neanderthals to be a wholly unknown hominin that was named after the cave where it was discovered. Other Denisovan remains were subsequently dug up in the cave, which has remains in sediments dating back about 300,000 years ago. The only other confirmed Denisovan from outside that Russian cave comes from a mandible bone part found in Tibet.
But the relative paucity of Denisovan bones doesn’t mean they were less common than Neanderthals. Gokhman suggests their population sizes weren’t very different. The reason more Denisovans haven’t been found is likely due to scholarly bias; much more research has been conducted on Neanderthals in Europe compared to Asia, where a focus on physical anthropology has only picked up in recent years. Genetic research on humans living today reveals that East Asians still carry Denisovan DNA — some of the adaptations that allow Tibetans to tolerate high altitudes is a gift from past humans interbreeding with these hominin relatives, for example.
"We know quite a bit about the DNA that they’ve contributed to modern humans. Some of it has been very useful,” says Alan Rogers, an anthropologist at the University of Utah.
Anthropologists there are just starting to look in likely places to see if they can discover more Denisovan remains. Some researchers believe that hominin remains found in eastern China may also be Denisovans, but researchers have yet to extract DNA from those ancient bones.
It’s difficult to separate Denisovans and Neanderthals at the best of times. To make matters more complicated, Denisova Cave also contains remains of a Neanderthal, as well as a fossil of a hybrid Neanderthal/Denisovan female, indicating these hominins certainly overlapped in time and space.
Rogers his colleagues believe that Neanderthals and Denisovans came from a common ancestor they call Neandersovans that spread out from Africa about 750,000 years ago. The Neandersovans spread across Eurasia, at which point the story gets even more complicated. Neandersovans interbred with a super archaic population of hominins that had spread out from Africa about 2 million years ago. In a study published in 2020, Rogers and his colleagues estimate this superarchaic hominin to have consisted of around 30,000 to 50,000 individuals. Shortly after spreading out of Africa, Rogers says Neandersovans split into distinct western and eastern populations. These in turn evolved into Neanderthals and Denisovans — though the two continued to interbreed for some time, as the remains at Denisova Cave reveal.
That interbreeding continued when modern humans migrated out of Africa. Today about 2 percent of Eurasian DNA contains Neanderthal genes. Denisovan genes are a little harder to nail down, Rogers says, but they likely exist in a similar proportion in the DNA of some East Asian populations today.
What’s the Difference?
For some time, we’ve know how Neanderthals differ from modern humans. Their faces stuck out more and they were a little shorter and broader. They had bigger brains than Homo sapiens, and longer arms. But there aren’t enough Denisovan bones to draw many conclusions about what they looked like. “There are so few bones that have been sequenced and are known to be Densiovan that we just don’t know about the Denisovan skeleton,” Rogers says.
That hasn’t stopped Gokhman from trying. He and his colleagues published a study that looked at how gene regulators present in Denisovan tissue might reveal what the hominins looked like. To hone their technique, they first applied their model to chimpanzees and Neanderthals. By looking at gene regulators alone, the scientists found they could predict the characteristics of chimps and Neanderthals with 85 percent accuracy. They then applied this method to Denisovan DNA, and came up with a few characteristics about features that might be smaller or larger than modern humans or Neanderthals.
Denisovan skulls were wider than both humans and Neanderthals, for example. Their faces stuck out more than human faces but not as much as those of Neanderthals. “In many ways, we predict them to be similar to Neanderthals, which makes sense because they are sister groups,” Gokhman says.
They also predicted wide skulls — a projection that matches with more recent discoveries of a skull that may be a Denisovan in Harbin China, though debate over whether that skull is of a Denisovan is divided. “They are expected to have the widest skulls ever seen because Neanderthals and modern humans already have very wide skulls,” Gokhman says.
Denisovans also had large teeth and longer dental arches than humans. In fact, a Denisovan jaw has been found since their predictions were made. “We actually see that seven out of eight of our predictions are validated in that jaw,” Gokhman says. Their pelvis is wider than humans and similar to Neanderthals — Denisovans are also believed to have matured faster than us but slower than Neanderthals when growing up. Finally, forget 1980s hair styles — Denisovans were the original flat tops, with flatter craniums than humans.
While it’s unfortunate that we don’t have a complete Denisovan skeleton to confirm many of these findings, increasing attention on hominin remains in Asia will improve our knowledge about the partial ancestors many modern humans inherited genes from. “Hopefully in the next few years we’ll find some Denisovans,” Gokhman says.