Pinky finger bone of a Denisovan girl found in the Denisova Cave
By Thilo Parg - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=41805194
In 2010, researchers analyzed DNA from a tiny 40,000 year-old fragment of a young girl’s pinky bone found in a remote Siberian cave and discovered a new type of prehistoric human. Named for the Denisova cave in the Altay mountains in which the fossil was found, the Denisovans were a group of archaic hominin (humans and close relatives) who coexisted with both Homo sapiens (modern humans) and Neanderthals, another species of prehistoric hominin. Denisovans ranged from Siberia to Southeast Asia and lived from around 400,000 years ago until an estimated 30,000 years ago. While Denisovans are different from other hominins in several ways, there is controversy over whether they should be classified as a distinct species because of how little is known about them.
Approximately 700,000 years ago, in Africa, Denisovans shared a common ancestor, Homo heidelbergensis, with both modern humans and Neanderthals. Then, the group that would form Neanderthals and Denisovans traveled into Europe and Asia, splitting off from the group that would form modern humans, which remained in Africa. Around 400,000 years ago, Denisovans and Neanderthals split, the Denisovans going East into Asia and the Neanderthals going West into Europe and Western Asia. After tens of thousands of years of separation, the habitats of the Neanderthals and Denisovans shifted and overlapped in some areas. After modern humans expanded out of Africa, they came into contact with the Denisovans around 40,000 to 60,000 years ago.
Map of the expansion of the Denisovans and evolutionary tree of the Denisovans and other human relatives
By John D. Croft at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=36145395
The discovery of the Denisovans was the first time that a new human group had been identified based on only DNA evidence. DNA had been preserved in the pinky bone by the cold weather of the Siberian cave in which the fossil was found. The researchers, led by Svante Pääbo, originally extracted mitochondrial DNA (DNA found in the mitochondria of a cell) from the pinky bone because each cell has thousands of copies of mitochondrial DNA, making it easier than extracting DNA from the nucleus, since each cell only contains two copies of nuclear DNA. Mitochondrial DNA does not contain nearly as much information as nuclear DNA, but it was enough for the researchers to tell that they were looking at an entirely new group of hominin with significantly different DNA from Homo sapiens and Neanderthals. Soon after, the researchers were able to sequence the nuclear DNA from the pinky bone to clarify the Denisovans’ relationship to Neanderthals and Homo sapiens. Around the same time, they also discovered a tooth in the Denisova cave, which came from a different Denisovan. This discovery emphasized that there was a population of these hominids, rather than only one unusual individual.
Interestingly, several different lineages of Denisovans have been discovered to have interbred with Homo sapiens. Many people living in Eastern Asia today have a small amount of Denisovan ancestry (while all non-Africans have a small amount of Neanderthal DNA). The Melanesians, people whose ancestors came from a Pacific Island region from Papua New Guinea to Fiji, have as much as 6% Denisovan DNA in their genomes. Researchers are still trying to determine how these pieces of Denisovan DNA might impact modern human health. Sherpas, ethnic Tibetans, have alleles (variations of genes) that come from the Denisovans which allow them to handle the lower oxygen at the high elevations of their native mountain region (the Himalayas).
Denisovans also interbred with Neanderthals. In 2018, researchers were able to identify a prehistoric girl who had a Neanderthal mother and a Denisovan father, based on DNA extracted from a bone fragment found in Denisova Cave. This girl, nicknamed Denny, lived around 90,000 years ago and is the only human that has been found to have parents from two distinct groups of hominin.
For a while, researchers were unsure of what the Denisovans looked like because the only fossils confirmed as Denisovan were the pinky bone, a piece of skull, a broken jaw, and several teeth. Then, in 2019, David Gokhman, Liran Carmel, and colleagues mapped out the skeletal structure of the Denisovan girl whose pinky bone had been found, based on DNA extracted from the bone. They discovered that Denisovans shared many skeletal features with the Neanderthals including heavy jaws, low foreheads, large rib cages, wide fingertips, and wide pelvises. However, they have several differences from both Neanderthals and modern humans including wider skulls. This study doesn’t necessarily describe what all Denisovans looked like because it only mapped out the skeletal structure of one girl, which may not be representative of the whole population. However, most of the study’s predictions fit with the few Denisovan fossils that have been found.
This study may allow researchers to identify unclassified fossils as Denisovan. There are many fossils throughout Asia that researchers have not been able to attribute to other hominin species, which could potentially be Denisovan. Researchers have not been able to extract DNA from those fossils because the hot climate in which they were found broke down the DNA. Two fragments of skull found in Xuchang, China have been tentatively identified as Denisovan based on the skeletal predictions of the study.
There’s still a lot to be learned about these intriguing human relatives, and advancements are being made at a rapid pace, so you can look forward to new discoveries about the Denisovans in the future.
About The Author
Marcella is currently a sophomore at Northwood High School. She is interested in biodiversity and animal behavior, and she plans to work in Conservation Biology. She plays the piano and also enjoys reading, baking, and being outside.
Sources
Than, Ker. “New Type of Human Discovered via Single Pinky Finger.” National Geographic.
National Geographic Society, 25 March 2010, https://www.nationalgeographic.com/history/article/100325-new-human-species-x-woman-pinky-finger-denisova-dna-nature. Accessed 27 November 2021.
Wei-Haas, Maya. “DNA reveals first look at enigmatic human relative.” National Geographic.
National Geographic Society, 19 September 2019, https://www.nationalgeographic.com/science/article/dna-reveals-first-look-enigmatic-human-relative. Accessed 27 November 2021.
Price, Michael. “Ancient DNA puts a face on the mysterious Denisovans, extinct cousins of
Neanderthals.” Science. American Association for the Advancement of Science, 19 September 2019, https://www.science.org/content/article/ancient-dna-puts-face-mysterious-denisovans-extinct-cousins-neanderthals. Accessed 27 November 2021
History.com Editors. “Denisovans.” History.com. A&E Television Networks, 21 August 2021,
https://www.history.com/topics/pre-history/denisovans. Accessed 28 November 2021.
New Scientist. “Denisovans.” New Scientist. New Scientist Ltd.
https://www.newscientist.com/definition/denisovans/. Accessed 28 November 2021.
Warren, Mathew. “Mum’s a Neanderthal, Dad’s a Denisovan: First discovery of an
ancient-human hybrid.” Nature. Springer Nature. 22 August 2018. https://www.nature.com/articles/d41586-018-06004-0. Accessed 28 November 2021.
Reich, D., Green, R., Kircher, M. et al. “Genetic history of an archaic hominin group from
Denisova Cave in Siberia.” Nature, vol. 468 1053–1060, 2010 https://www.nature.com/articles/nature09710. Accessed 28 November 2021.
Wei-Haas, Maya. “Multiple lines of mysterious ancient humans interbred with us.” National
Geographic. National Geographic Society, 11 April 2019. https://www.nationalgeographic.com/science/article/enigmatic-human-relative-outlived-neanderthals. Accessed 28 November 2021.
Comments