A new study from China’s Lanzhou University has shown for the first time the presence of Denisovan DNA somewhere other than in Siberia's Denisova Cave. That is a big deal since almost all of us carry some of that DNA within our own genomes.
Who were the Denisovans?
In 2010, scientists from Russia's Institute of Archaeology and Ethnology of Novosibirsk were continuing their excavations at the Denisova Cave located in the Altai Mountains of south-central Siberia.
Working in strata dated between 76,200 and 51,600 years ago, the tiny finger bone of a child was found. When scientists from Germany's Max Planck Institute for Evolutionary Anthropology analyzed the bone, sparks flew.
The bone was from an entirely new type of human, or hominin, and they were christened "Denisovans" after the cave in which the bone was found. The Denisovans, or Homo denisovan, now joined Homo sapiens and Neanderthals as a distinct form of humans.
In 2019, Greek archaeologist Katerina Douka and colleagues radiocarbon-dated the oldest specimens from Denisova Cave, and they came up with a startling age of between 195,000 and 122,700 years ago. When they radiocarbon-dated artifacts that were found within the cave, the date came in at a staggering 287,000 years ago.
Up until 2019, only Denisova Cave contained evidence of this elusive species, with specimens from five distinct Denisovans having been found. Then, scientists at Lanzhou University examined a partial mandible, or jaw bone, that had been part of the university's collection since 2010.
Originally discovered in the Baishiya Karst Cave in 1980 by a Buddhist monk, when scientists examined the jaw bone, they discovered that it belonged to a Denisovan who lived over 160,000 years ago. That date is a full 100,000 years before the first modern humans arrived in the area.
Located on the Tibetan Plateau, the Baishiya Cave sits at a height of 10,760 feet (3,280 m) above sea level, while the Denisova Cave is only 2,296 feet (700 m) above sea level. Soil samples taken from the Baishiya Cave and analyzed at Arizona State University (ASU) indicated that Denisovans may have been occupying the cave up to 45,000 years ago. That date is significant because it means that Denisovans and modern humans were living side by side at the same time in central Asia.
Many forms of us
Denisovans and Neanderthals split from modern humans about 804,000 years ago, then from each other about 640,000 years ago. This means that Denisovans are the descendants of an earlier migration of H. erectus out of Africa and that they are completely distinct from modern humans and Neanderthals. Indeed, the exceedingly large molars of Denisovans are similar to those of Australopithecines.
This adds to the debate over whether Homo sapiens solely evolved in Africa, or whether our evolution continued in Asia. Also found in the Denisova Cave alongside the child's finger bone were bone tools, a marble ring, an ivory ring, an ivory pendant, a red deer tooth pendant, an elk tooth pendant, a chloritolite bracelet, and a bone needle. This indicates that Denisovans may have been making sophisticated tools and jewelry.
Denisovans are among us
Denisovans definitely interbred with modern humans, a fact that is borne out by modern Sherpas who live on the Tibetan Plateau. At 13,123 feet (4,000 m) above sea level, the Sherpas have a genetic adaptation to high altitudes that came from Denisovans. This adaptation allows them to live where oxygen levels are 40% less than that of the sea level.
Within the cells of all of us are mitochondria, which are small, rod-like power plants, and those of Sherpas are highly efficient at using oxygen. Sherpas' muscles get more mileage out of less oxygen than any other humans.
Statistical geneticist Sharon Browning of the University of Washington in Seattle and colleagues have also found traces of Denisovan DNA in populations throughout Australia and Melanesia. Melanesia is comprised of the islands northeast of Australia. Between 3% and 5% of the DNA of Aboriginal Australians and Melanesians is from Denisovans. Between 7% and 8% of the Papuans' DNA who live in Indonesia is from Denisovans.
Modern humans and Denisovans may have interbred with one another as late as 14,500 years ago in New Guinea. Denisovans also interbred with Neanderthals, with about 17% of the Denisovan genome that was found in the Denisova Cave deriving from Neanderthals.
Of the five Denisovan specimens found in Denisova Cave, one was a young woman who has been nicknamed "Denny". She was a Denisovan/Neanderthal hybrid whose father was a Denisovan and whose mother was a Neanderthal.
Several different species of animals can interbreed with one another, however, their offspring are usually infertile. Examples of species interbreeding include:
- Zebra + any other Equine = Zebroid
- Lion + Tiger = Liger, produced by a male lion and a tigress, it is the largest of all known felines
- Bottlenose Dolphin + False Killer Whale = Wholphin, while reported in the wild, two exist at Sea Life Park in Hawaii
- Grizzly Bear + Polar Bear = Grolar Bear
- Domestic Cattle + American Bison = Beefalo, this cross has led to genetic pollution of American bison herds
- Serval Cat + Domestic Cat = Savannah Cat, first bred in 1986, in 2001 the International Cat Association accepted it as a new registered breed
- Male Donkey + Female Horse = Mule, known to be infertile, mules are patient, sure-footed, and hardy
- Male Dromedary Camel + Female Llama = Cama, first produced in 1998 at the Camel Reproduction Center in Dubai
- Yak + Domestic Cattle = Dzo, they are larger and stronger than regular cattle or yaks
- Wolf + Dog = Wolfdog, wolves are usually bred to German Shepherds, Siberian Huskies, or Alaskan Malamutes, and their behavioral characteristics are unknown.
Of all people living today, except those from sub-Saharan Africa, around 2.8% of our DNA comes from Neanderthals. However, when scientists at the University of Utah analyzed the genomes of Europeans, Asians, Neanderthals, and Denisovans, they concluded that the latter two must have mated with a super-archaic "ghost hominin" that had separated from Homo sapiens around 2 million years ago.
Candidates include Homo erectus and Homo heidelbergensis, and this interbreeding might have extended to up 600,000 years ago. Another "ghost hominin" is found in the DNA of those living on the island of Flores, and only in the DNA of short-statured people who live near the Liang Bua Cave. This cave is where fossils of Homo Floriensis, better known as the "Hobbit", have been found. A skeleton found in 2003 stood 3 feet 7 inches (1.1 m) tall while stone tools also recovered in the cave date to between 50,000 and 190,000 years ago.
ASU's Charles Perreault told the Daily Mail that, "... Denisovans, like Neanderthals, were not mere offshoots of the human family tree. They were part of a web of now-extinct populations that contributed to the current human gene pool and shaped the evolution of our species in ways that we are only beginning to understand."