The Denisovans were an ancient human population that once roamed the Earth alongside the Neanderthals and modern Homo sapiens. However, nobody knew about them up until a path-breaking discovery in the Denisovan Cave in Siberia.
In 2010, an analysis of mitochondrial DNA extracted from a finger bone found in the Denisova Cave in the Russian Altai revealed the existence of a new hominin taxon. This newly described group was found to be genetically distinct from both Homo sapiens and homo neanderthalensis. The bone, dating back to the Initial Upper Paleolithic, opened up a whole new chapter in our understanding of human evolution.
But it did not stop there! Thanks to the power of ancient DNA analysis, researchers have been able to piece together the story of the Denisovans, their migration patterns, and even their interactions with other human species. The Denisovan DNA has revealed fascinating insights into our own genetic makeup, such as their contributions to our immune system, metabolism, and even the ability to adapt to high altitudes.
The small bone fragment, from a girl’s little finger, discovered from the Denisova Cave was sent to Svante Pääbo, the Head of the Department of Genetics at the Max Planck Institute of Evolutionary Anthropology. Through genetic analysis, it was revealed that the bone belonged to a previously unknown hominin, which was named Denisovan after the cave. Subsequent analysis of a tooth from the cave also confirmed its Denisovan origin.
The Denisovans were identified as a distinct group based on analysis of mitochondrial DNA sequences, which showed haplotypes outside the range of variation of modern humans and Neanderthals. Haplotypes are sets of genetic variants located on a single stretch of the genome, and they can be used to differentiate groups and determine their relationships.
The mitochondrial DNA sequence of Denisovans, called lineage X, indicated that they diverged from modern humans and Neanderthals around one million years ago. However, analysis of the nuclear genome showed that Denisovans are actually a sister group to Neanderthals, suggesting a closer relationship than indicated by the Mitochondrial DNA data.
Molecular data suggests that the split between Neanderthals and Denisovans occurred between 380 to 470 thousand years ago, while the branch leading to Denisovans and modern humans diverged around 800 thousand years ago. The Denisovans are also more closely related to another set of fossils found in the Sima de los Huesos cave in spain, dated to 480 thousand years ago indicating that the split between Neanderthals and Denisovans must have occurred before that time.
The study of ancient DNA has revealed significant genetic differences between Denisovans and modern humans. Denisovan genomes differ from the standard human genome by 11.7%, while the difference between Neanderthals and modern humans is 12.2%. Denisovans and Neanderthals are closely related but distinct from Homo sapiens.
Modern non Africans have about 2 to 4 % Neanderthal ancestry, while Denisovans did not contribute to the Neanderthal human admixture. However, Denisovan ancestry makes up 3 to 6% of the gene pool in Southeast Asia, Australia, and Oceania.
Denisovans show higher genetic diversity than Neanderthals but lower diversity than modern humans, indicating a larger and more diverse population. Their geographic distribution ranged from North Asia to Southeast Asia.
Denisovans likely played a role in adaptive introgression, where early Homo sapiens acquired genes from Denisovans that enhanced adaptation, disease resistance, and immune systems. The presence of human leukocyte antigens in modern humans, inherited from Denisovans, supports this hypothesis. For example, there are evidences that adaptation to high altitude hypoxia among modern day Tibetans is a result of introgression from Denisovans
The populations of eastern Indonesians, Papuans, Philippine “negritos,” Siberians, South Asians, and East Asians, are among the few existing groups that exhibit substantial traces of genetic material from Denisovans. It is worth noting that the region of Island Southeast Asia and Papua which consists of numerous densely inhabited archipelagos, holds some of the earliest evidence of early archaic humans outside Africa. Additionally, it is believed that archaic hominins like Homo floresiensis coexisted with modern humans in this region.
Modern Australian aboriginals and Papuans have the highest proportion of around 5 to 6% of Denisovan ancestry, while American and mainland Asian populations have a smaller proportion about 0.2%. This suggests interbreeding between Denisovans and early modern humans during the early dispersal of humans in Asia.