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TODAY, there is only one species of human alive on the planet. But it wasn鈥檛 always so. For millions of years, and until surprisingly recently, there were many types of human-like groups, or 鈥渉ominins鈥�. They coexisted, perhaps they fought, and they interbred. It would be fascinating to know how these others lived, but understanding who they were and what they were like is extremely challenging. We cannot put ourselves into their minds, and we have only fragmentary clues from fossils and artefacts they left behind to reconstruct their lives.

That challenge is especially daunting for one of these extinct groups, the Denisovans. Discovered just a decade ago, the Denisovans have left us scant physical evidence. Instead, our knowledge of them comes almost entirely from their preserved DNA. It tells us that they are a sister group to the Neanderthals, that they lived in Asia for hundreds of thousands of years and that they interbred with our species. But we don鈥檛 know what they looked like, how they walked or if they could speak.

Now, that is changing. In the past few years, archaeologists have alighted on a few fossils that seem to be Denisovan. They have also unearthed treasure troves of artefacts, including tools, jewellery and even art, that they think were created by these mysterious people. These interpretations are potentially explosive, so it is hardly surprising that some dispute them. Nevertheless, we are starting to piece together a picture of the Denisovans, one of our closest cousins, and a group that still lives on in the DNA of many people today.

The discovery of the Denisovans came as a total surprise, partly because it played out differently from the uncovering of every other extinct human group. The story starts in the Altai mountains in southern Siberia, Russia. For decades, archaeologists have been excavating in Denisova cave 鈥� named after a hermit called Denis who lived there in the 18th century. Hominins have inhabited it on and off for hundreds of thousands of years. Most were Neanderthals who, although most prevalent in Europe and west Asia, sometimes made it as far east as the Altai.

In 2008, archaeologists led by Michael Shunkov at the Russian Academy of Sciences in Novosibirsk discovered a fragment of finger bone in the cave. Assuming it belonged to a Neanderthal, Shunkov sent it to Svante P盲盲bo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. P盲盲bo鈥檚 team extracted DNA from the bone and found it didn鈥檛 match Neanderthal DNA 鈥� or modern human DNA. It was something never seen before. After initially referring to the individual as 鈥淴-飞辞尘补苍鈥�, Shunkov and P盲盲bo settled on 鈥淒enisovans鈥� as a name for the group.

The findings were . Never before had a group of hominins been identified solely from its DNA. Another surprise was to come, however. Some of the Denisovan DNA sequences matched those found in people living on the islands of Melanesia, especially Papua New Guinea. The implication was that thousands of years ago, Denisovans and members of our species, Homo sapiens, had sex and produced children. As a result, today around 5 per cent of the DNA of Melanesian people is Denisovan, with many of these genes appearing to .

In itself, the interbreeding wasn鈥檛 too big a shock. P盲盲bo鈥檚 team had published the sequence of the Neanderthal genome earlier in 2010, revealing that H. sapiens and Neanderthals interbred, and that all humans today whose ancestral group developed outside Africa carry some Neanderthal DNA. But the Denisovan interbreeding was odd because their DNA was found thousands of kilometres away from Papua New Guinea in Denisova cave. The implication was that Denisovans were once widespread. In fact, their 鈥渄emographic and evolutionary core鈥� was probably in south Asia, says Jean-Jacques Hublin, also at the Max Planck Institute for Evolutionary Anthropology.

This was all based on DNA from a single finger bone. There was no skeleton, and no artefacts. The Denisovan people themselves were a total mystery. A study published in 2019 sought to address this by using the Denisovan genome to deduce what they looked like. Researchers identified methyl 鈥渢ags鈥� attached to the genome, which reveal how active each gene was, and used that information to generate an image of a Denisovan face. However, the study was widely disputed, not least because nobody has ever even shown that .

If the genome cannot tell us what Denisovans looked like, we must find out the old-fashioned way 鈥� by excavating Denisovan remains. To that end, people have been exploring sites in China and nearby countries, and scouring old museum collections. For almost a decade, there was nothing. Now there is.

, a palaeoanthropologist at the University of Toronto in Canada, has found several skull fragments in Denisova cave. Details haven鈥檛 been published yet, but viewing a cast of one over Zoom reveals that the bone is unusually thick. To Viola, this suggests that Denisovans were big 鈥� perhaps more than 100 kilograms 鈥� with 鈥淎merican football player body build鈥�. Analysis of their genome reveals it contains DNA from an unidentified older population: could they have interbred with the decidedly bulky Homo erectus, a species that lived on in east Asia long enough to have met them?

High society

These fragments are the best Denisovan fossil evidence found so far at the cave, but archaeologists have expanded the search. A crucial clue emerged in 2014. now at Brown University in Providence, Rhode Island, and her colleagues were , which is involved in the body鈥檚 response to low oxygen levels. People living on the Tibetan plateau, more than 4 kilometres above sea level, have a modified version of EPAS1 that helps them cope with the thin air. Huerta-S谩nchez found that this came from interbreeding with Denisovans .

Denisova cave is only 700 metres above sea level, so it seems unlikely that the mutation arose there. But it would have been a useful adaptation if Denisovans were living at high altitude elsewhere. Tentative evidence of this emerged in 2018. At Nwya Devu on the Tibetan plateau, a research team found buried between 40,000 and 30,000 years ago that might have been left by Denisovans 鈥� or H. sapiens.

More compelling evidence comes from Baishiya Karst cave in Xiahe in the north-east of the Tibetan plateau. It is a sanctuary for Tibetan Buddhists and, in 1980, a . 鈥淟ocal people used to collect bones in this cave to grind, to make some kind of medicine,鈥� says Hublin. 鈥淟uckily, this monk did not grind the fossil.鈥� Instead, it was sent to Lanzhou University in China. It doesn鈥檛 contain any preserved DNA, but, in 2019, Hublin and his colleagues revealed that they had managed to This matched protein found in Denisovans. They also concluded that the jawbone was at least 160,000 years old.

Many people found it hard to accept that Denisovans were living in one of the harshest environments on Earth 160,000 years ago. But, in October 2020, researchers led by Qiaomei Fu at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, reported finding of Baishiya Karst cave. The DNA samples dated from 100,000, 60,000 and possibly also 45,000 years ago. Not only were the Denisovans there, it looks as if they were there for at least 115,000 years, plenty of time to evolve adaptations like the modified EPAS1 gene. 鈥淚 was a little more sceptical in the beginning,鈥� says Viola. But the sediment DNA sealed the deal. 鈥淚鈥檓 really convinced.鈥�

That means we now have another Denisovan specimen, with its own story to tell. The overall shape of the jawbone is typical for hominins of the time. Some features are quite Neanderthal-like, which Hublin says is to be expected of a sister group. What marks it as Denisovan are its enormous teeth. Ongoing excavations at Denisova cave have yielded three Denisovan teeth, all also whopping. 鈥淭he Denisovans are really weird,鈥� says Shara Bailey at New York University. Throughout human evolution, teeth have generally shrunk, but they bucked that trend. 鈥淣eanderthals and Homo sapiens both have small teeth, so I would suggest that their shared ancestor also had small teeth, which would suggest the big teeth in Denisovans is something they evolved later,鈥� she says.

A likely explanation is that they had to chew tough or hard foods. Unfortunately, attempts to recover traces of food from the teeth have so far failed. However, if DNA in sediments at Denisova cave is anything to go by, Denisovans who lived there ate a range of large animals, such as deer and horses. They even seem to have including snow leopards, bears and hyenas, according to William Rendu at the National Centre for Scientific Research in Bordeaux, France, who led the analysis. , stone tools from the cave have traces of animal fat on them. Rendu believes that the Denisovans probably hunted with spears, even though the wooden shafts haven鈥檛 been preserved in Denisova cave. Hominins appear to have been using spears for , so it wouldn鈥檛 be surprising that the Denisovans could make them.

Tech savvy

Meat can certainly be tough to chew, unless you cook it. 鈥淭here is some evidence of fire in Denisova cave,鈥� says Rendu. Indeed, controlled fire use became common in Eurasia after 400,000 years ago and Neanderthals probably used several cooking techniques. But the looks intermittent, so it isn鈥檛 clear if Denisovans cooked too. If not, that might explain their unusually large teeth.

However, Rendu notes that there is almost no difference between what the Denisovans and Neanderthals living in Denisova cave ate. This suggests they had similar capabilities. 鈥淐learly, we should expect the same levels of technology, same levels of thinking,鈥� he says. Artefacts unearthed by Shunkov and his colleagues at the cave seem to back this up. Almost 80,000 objects, laid down over 150,000 years, reveal a steady progression from flat stone flakes to narrow blades and chisels. This is exactly the technological progression that Neanderthals and H. sapiens were making at that time. Yet the researchers argue that .

Such claims are hard to prove and some people dispute this assertion. 鈥淵ou need to have the stone tools in the cold, dead hand of the hominin,鈥� says Sheela Athreya at Texas A&M University. And provenance is especially difficult to establish at Denisova because habitation by Denisovans and Neanderthals overlapped. In 2018, geneticists reported discovering that a 90,000-year-old bone fragment belonged to a young girl they nicknamed 鈥淒enny鈥�, who had a Neanderthal mother and Denisovan father. Finding such a child of the two types of early human would be astonishingly unlikely unless interbreeding, and thus population overlaps, were common.

Intriguingly, stone tools have also been found in Baishiya Karst cave. 鈥淭hey date back possibly around 190,000 years,鈥� says Fu, suggesting that Denisovans made them. No details have been published, but according to Hublin, 鈥渋t鈥檚 quite different from what they have in Denisova鈥�.

Meanwhile, Shunkov has an even bigger claim: by around 60,000 years ago, the . Artefacts his team has found in Denisova cave include bone beads, a marble ring, a button made of mammoth ivory and a polished bracelet of dark green rock. This claim is so hotly disputed that many researchers are unwilling to discuss it. But Viola notes that Neanderthals made jewellery out of . He is comfortable with the idea that Denisovans made similar objects, but says that some of the finds look too advanced. 鈥淭hat polished stone bracelet, that鈥檚 a level of technology that we don鈥檛 even see modern humans doing till less than 10,000 years ago. I don鈥檛 think Denisovans could have done that.鈥�

The other issue is the age. A 2019 analysis led by Katerina Douka at the Max Planck Institute for the Science of Human History in Jena, Germany, concluded that the most recent clear evidence of Denisovans in the cave is no younger than 52,000 years old, but tooth pendants and bone points found there . This suggests that H. sapiens made the most advanced artefacts.

The same problem bedevils claims of Denisovan art. In 2019, a team described two pieces of bone that had been carefully scratched with a sharp point and coloured with red ochre. They were found at Lingjing in northern China and are . That is early enough to be Denisovan, but also late enough to be made by H. sapiens. A beautiful Indonesian cave painting, showing human-like people hunting pigs and buffalo, is around 44,000 years old 鈥� an even more ambiguous date.

If some of these objects turn out not to have been made by Denisovans, it doesn鈥檛 mean they weren鈥檛 clever, says Athreya. 鈥淣ot all societies have to have Western markers of civilisation to be smart.鈥� In fact, symbolic behaviours like making art may not become established in small, isolated populations, which, genetic evidence suggests, is how Denisovans lived. 鈥淪ymbolic thoughts, symbols like personal ornaments and art and body decoration, would be important when you鈥檙e trying to identify 鈥榰s鈥� versus 鈥榯hem鈥�,鈥� says Bailey. If most Denisovans rarely met other groups, art may not have been a priority.

鈥淒enisovans inhabited one of the harshest environments on Earth鈥�

Nevertheless, the Denisovans鈥� apparent technological sophistication, hunting prowess and ability to survive in extreme environments are impressive. And they were clearly able to get along with other hominins when they did meet. The working hypothesis should be that they were intellectually on a par with Neanderthals, says Viola. Historically, Neanderthals were portrayed as stupid, but that stereotype has been overhauled. 鈥淐ognitively, they weren鈥檛 that different from us,鈥� says Viola. 鈥淚f Neanderthals weren鈥檛 that different, Denisovans shouldn鈥檛 be either.鈥�