For a people from whom one 41,000 year old finger bone fossil from a nine year old girl, along with a bracelet she wore, were (until recently) the only authenticated known artifacts, the mysterious Denisovans sure received lots of publicity. Both scholarly journals and popularly oriented science magazines were quick to pick up on any academic or speculative news from the fields of anthropology and archaeology tied to them in some way or other. These artifacts were discovered in the 1970’s by Soviet paleontologist Nicolai Ovodov.

Even the name assigned to the group has its origin in a somewhat spiritual, rather than more conventional way. Denis the Hermit was a Russian Orthodox religious contemplative who lived in the cave named for him during the 18 th Century. The cave is located in the Altai Mountains of Central Siberia, not far from where borders of Russia, Mongolia, and China meet. Long before Denis, various early humans made the cave home, and more recently, sheep herders sporadically occupied it.

Origin of the Denisovans

However, first speculation about the Denisovans came long before they were given their name, and many miles to the east, as scholars decided they belonged in the Balkans, Ukraine, and Kazakhstan. Why? It seems anthropologists had noticed that Neanderthal fossils and artifacts had always been found in Western Europe and the Middle East.

Some reasoned that either Neanderthals or some counterpart peoples also logically belonged east and northeast of these places too, and now, with the Denisovan finding, this might be the case. In fact, to some scientists and prehistoric-interested laymen, Neanderthals and Denisovans became ‘cousins’.

Their origins were dated to around 300,000 years ago, when Homo sapiens and Neanderthals both emerged from Africa during a pluvial period caused by a continental glacier occupying much of Europe. This wetter climate had given most of North Africa a livable environment. With much of the world’s water locked up in European, Siberian, North American, and Antarctic ice sheets, the lowered water levels of the Mediterranean and Red Seas allowed first Neanderthals, then Homo sapiens , also known as Cro Magnon Man, to walk across at dry points.

Neanderthals, since discovery of their fossils in the late 19 th Century, were characterized as brutish, more primitive than Homo sapiens, some scholars even claiming sub-human status and lack of linguistic abilities for them.

Prominent brow ridges on their skulls contributed to this view, as bonobos, chimpanzees, and gorillas also have them. Early textbooks theorized that as subsequent waves of Homo sapiens arrived on the scene, the two species clashed, gradually wiping out the unfortunate Neanderthals.

Then as the 21 st Century dawned, researchers discovered that former authorities had been mistaken. Hybrid fossils from interbreeding of the two species were discovered and geneticists declared that many modern Homo sapiens possess small levels of Neanderthal genes . Those earlier arrivers to Europe hadn’t been wiped out after all but assimilated.

Hybrid fossils reveal interbreeding between Homo sapiens and Neanderthals. (Abuk SABUK / CC BY-SA 3.0 )

Farther to the East, scientific speculation was focusing as well. In the 1980’s on the Tibetan Plateau, a Buddhist monk investigating a karstic cave found an adult human jaw bone with similarities to Neanderthal fossils. The relic was turned over to researchers at Northern China University, who sequenced its protein to determine an age of 160,000 years ago. These scholars pronounced it to be Denisovan.

This placed it at the height of the last glacial, or Wisconsin epoch, making it much more ancient than the little girl’s finger bone, which was dated to when the continental glaciers were starting to recede.

Denisovan Migration

By now, various scientists were speculating about Denisovan migration routes, hypothesizing that they moved southeasterly, passing from mainland Asia into Indonesia, Papua New Guinea, Melanesian Island chains, and possibly even Australia. Migration routes like these would have been realistic, because since the continental glaciers were at their height, sea levels would have been low enough to facilitate dry land journeys.

The evolution and geographic spread of Denisovans as compared with Neanderthals, Homo heidelbergensis, and Homo erectus. (Cmglee / CC BY-SA 3.0 )

When glaciers were largest, covering vast expanses of continental land masses, and even many parts of high mountain ranges in lower latitude regions, human migrations become easier. People could now walk between what were islands during warmer times. Scientists were able to calculate where shorelines would have been located at various times during past history, both by estimating former glacial sizes and finding evidence of shoreline erosion and deposition.

This data, when applied to places now separated by water from each other, like Morocco from Spain/Gibraltar, Tunisia from Sicily and Italy, or Southeastern Asia from the Philippines, Indonesia and Australia, reveals where ancient migrations occurred and roughly when.

A special case arises when this sea level change calculating is applied to northeastern Siberia and northwestern North America. Here we have glaciers sometimes blocking migration routes, definitely not the case with North Africa/Southern Europe or southeast Asia/Pacific archipelagos or Australia. These migration routes were located in relatively warm climatic areas where ice sheets didn’t form.

Enter Beringia, the landmass that once existed during glacial times when large portions of the northeast Asian and Alaskan continental shelves, now under the Arctic Ocean, was dry land. To their south, so was most of the Bering Sea, including the island arc stretching from the Kodiak Peninsula of Alaska through the Aleutian and Komandorski Islands, all the way to the northern Kamchatka Coast.

Beringia, the landmass that existed during glacial times was dry land. ( Lukas Gojda / Adobe)

When Beringia wasn’t blocked by ice (during the times the glaciers were either forming or melting) Beringia was the land bridge for people and animals to enter North America from Asia. It would become a bridge for back migrations also, a little later during geologic time.

When the glaciers were gone, except in Greenland and Antarctica, as they are today, one tiny remaining piece of Beringia was still a bridge for people, as the two Diomede Islands, one in the United States, one in Russia, are visible from each country. In more recent ancient times, when early man had mastered boat-making and ocean-going navigational technology, his vision of land on the horizon spurred migration across water.

Today, Native American tribal and scholarly historians cite ancient tribal legends of crossing water from an old land to a new one. By then, however, the Denisovans were long gone.

Just how long ago were the great continental glaciers at just the right size and sea levels just the right height for persons to cross into Beringia on foot?

Beringia coverage at the time of the Denisovan. (Roblespepe / Public Domain )

Glaciologists, geologists, climatologists, and anthropologists have all had a hand in estimating the age, number, and magnitude of so-called glacial epochs and the warmer interludes between them. Current thinking is that dating way back to before life of any kind existed, there have been nine so-called glacial ages. We are still experiencing the present one, often called the Pleistocene Epoch, which began about 2,600,000 years ago. In it there have been eleven interglacial or warmer periods, lasting for about ten to thirty thousand years each.

The next-to-last one, sometimes called Eemian Interglacial, lasted roughly from 130,000 to 115,000 years ago. It was a little warmer than the present warmer period, usually called Late Cenozoic Interglacial or Holocene, which is still going on. During the height of the Eemian, palm trees grew as far north as the Alaskan Panhandle. The Late Cenozoic period began around 15,000 years ago and as everyone conversant with political discussions and debates knows, is continually still getting warmer.

During the Eemian period palm trees grew in the Alaskan Panhandle. ( freedom_wanted / Adobe)

When both Eemian and Late Cenozoic dates are applied to human migrations, several speculative observations suggest themselves. In tropical and sub-tropical latitudes only sea levels are relevant because glacial blockage isn’t a major factor, whereas in Beringia, both harsh subarctic climate and glacial blockage present obstacles as well. However, in the Late Cenozoic only, human cultural evolution brought use of boats onto the scene thus partially negating the obstacles created by rising sea levels. This factor largely applied to areas where early man could view land on the horizon thus risking pushing onward.

Denisovan DNA in America

While both scientists and hobbyists who like early human lore were speculating about who, when, and how humans crossed Beringia from Asia into North America, others of like ilk were pursuing hard answers. Geneticists were busy pushing the boundaries of DNA and protein analysis further and further, whereas earlier radio carbon, strontium, and oxygen-18 dating technologies had been useable only in limited situations. Linguistic anthropologists started to compare languages using computer techniques and to take tribal legends more seriously.

Aerial photography and satellite imagery was finding its way into archaeology. Now it was time to ask an almost sacrilegious question for some, “Did the Denisovans make it into North America?” Or if not, would traces of their DNA turn up among New World peoples, just as Neanderthal DNA had been found in genes of some modern Europeans?

Initially, scholars and hobbyists alike assumed human migration through Beringa occurred only during the Late Cenozoic, during which three distinct migration waves had been identified. Then two additional factors emerged suggesting that Eemian times must have seen some activity too. (1) The scrub vegetation growing in Beringia during the colder Late Cenozoic wouldn’t have supported the large grazing animals like mammoths, mastodons, horses, and camels that once thrived in the Americas.

Researchers like David Reich of the Harvard Medical School and his colleagues suggested that a 40,000 year negative selection Neanderthal and Denisovan genes existed among many Southeast Asians and Pacific Islanders . Would there be time for DNA influences to be carried far and wide in the Western Hemisphere from Late Cenozoic arrivers who had crossed Beringa? These same scientists also found Denisovan genes in the Americas and far north-east Asia.

Pleistocene Tools discovered at the Calico Early Man Site. (Travis / CC BY-SA 2.0 )

Other scientists, while not as concerned with Denisovans or DNA evidence, found evidence far to the south of Beringia in both North and South America that suggested human presence dated earlier than the Late Cenozoic. While still not fully authenticated, the Calico site in California was alleged to date as early as 200,000 ago. If this proves to be accurate, it would strongly suggest some humans crossed Beringia during a third-last interglacial warming period. While not citing specific dates, eminent archaeologist Louis Leakey was one of the scientists claiming Calico is a bona fide early man site.

Chile, of all places, has several purported early man sites. Monte Verde in central Chile containing fossils and a human footprint, has been dated to 18,500 BC, placing it about 2,500 years before Beringia became useable for Late Cenozoic migrants. Other Chilean investigators have made claims for fossil remains of agricultural-type planted crop rows.

Many Denisovans scholars have long been making a case for the fact that if early Late Cenozoic had made it across Beringia, it would take longer for their descendants to travel to southern South America to occupy sites there, given the verified dates for those sites. In other words, their ancestors must have arrived during the Eemian.

Examining the migrants that crossed Beringia during the Late Cenozoic, we find they are divided into three distinct, somewhat dissimilar groups. More genetic research is needed before who had and who hasn’t had some Denisovan genes is known. The last of the three, the Athabascans, also sometimes called Na Dene, were still migrating southward when the first European colonists were arriving on North and South American east coasts. While some Athabascans remained in Alaska or Yukon, others pushed on to Arizona, New Mexico, and northern Mexico, where they are today, known as the Navajo and Apache tribes. All New World Athabascans have close cultural and genetic affinities with the Chukchi of far northeastern Siberia.

If any Denisovans were among the groups who crossed Beringia, it had to be during the Eemian. The Late Cenozoic appears to be too late and the third-last interglacial period is probably too early, or if not, too nebulous to make any determinations. Whether their DNA crossed the bridge, as part of the living bodies of people whose ancestors mated with Denisovans , that answer has to be “yes.” What is yet unknown, are the specifics - who mated with whom, where, and when.

Only partially known is the fascinating story of folks who almost became ‘ape men’ and ‘ape women’, and only now are emerging as one more valuable piece in the puzzle that constitutes the story of human civilization.

Top image: Finger bone fragment containing Denisovan DNA. Source: Thilo Parg / CC BY-SA 3.0 .

By Glenn Dahlem, Ph.D