In a groundbreaking discovery, an international team of scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig has sequenced mitochondrial DNA from an ancient finger bone found in the Denisova Cave in the Altai Mountains of southern Siberia. The bone, estimated to be between 48,000 and 30,000 years old, belongs to a previously unknown form of human that inhabited the region during the late Pleistocene. This discovery is not only significant in terms of genetic findings but also sheds light on the complexities of human migration and evolution during a pivotal period in history.
The mitochondrial DNA extracted from the finger bone offers a glimpse into the genetic legacy of a human group that diverged from both Neanderthals and modern humans. The study of this DNA, which is inherited solely through the maternal line, has revealed that this particular hominin represents a distinct migration event out of Africa, separate from the well-known migrations of Homo erectus, Neanderthals, and modern Homo sapiens. The findings were published in Nature in March 2010 and have opened up new avenues for understanding human evolution and the diversity of hominin species that existed during this time.
To understand the significance of this discovery, it’s important to first examine the broader context of human migration out of Africa. The first major group of hominins to leave Africa was Homo erectus, which began migrating about 1.9 million years ago. Fossil evidence and genetic data suggest that Homo erectus dispersed into various regions, including Asia and Europe, where it evolved into several distinct species. One of these was Homo heidelbergensis, the ancestor of both Neanderthals and modern humans.
Approximately 500,000 to 300,000 years ago, a second wave of migration occurred, with the ancestors of Neanderthals branching out from Africa. Neanderthals spread throughout Europe and parts of western Asia, adapting to the colder climates of the time. Around 50,000 years ago, the ancestors of anatomically modern humans began their migration out of Africa, eventually spreading across the globe and replacing or interbreeding with other hominin species along the way.
However, the Denisova hominin, as this newly discovered human form is called, represents an even earlier migration that had previously remained undetected. The mitochondrial DNA recovered from the ancient finger bone is distinct from that of both Neanderthals and modern humans. Through careful analysis, the research team determined that the lineage of the Denisova hominin diverged from the common ancestor of Neanderthals and modern humans about 1 million years ago. This suggests that the Denisova hominin shared a common ancestor with both groups but had been evolving separately for a significant period before the mitochondrial lineages of Neanderthals and modern humans became distinct.
The discovery of the Denisova hominin provides crucial evidence for a third migration event out of Africa, which was not previously identified in the fossil record. It indicates that another group of humans left Africa before the ancestors of Neanderthals and modern humans, possibly around 1.5 million years ago, and settled in regions like Siberia, where they evolved in isolation. This new form of human appears to have coexisted in the same regions as Neanderthals and modern humans, particularly in southern Siberia, where their paths may have occasionally crossed.
The finger bone from the Denisova Cave is not the only artifact associated with this enigmatic group of humans. Further excavations in the cave have uncovered additional fossil fragments, including teeth and a jawbone, suggesting that a small population of these hominins lived in the region during the late Pleistocene. These findings raise intriguing questions about their physical characteristics, lifestyle, and interactions with other human species.
Unlike Neanderthals, whose remains have been found across Europe and parts of Asia, the Denisova hominin appears to have been largely confined to a specific area in the Altai Mountains. The mitochondrial DNA extracted from the finger bone suggests that this group was genetically distinct, with no known overlap with other contemporary hominins in the region. It remains unclear whether the Denisova hominins were physically different from Neanderthals or modern humans, but some genetic evidence suggests that they may have had a unique set of traits.
The implications of this discovery extend beyond the genetic evidence itself. The mitochondrial DNA analysis shows that the Denisova hominin had a common ancestor with both modern humans and Neanderthals, but was a separate lineage that evolved independently. This makes them an important piece of the puzzle in understanding the broader picture of human evolution. This also suggests that the migration of early humans out of Africa was much more complex than previously thought, with multiple waves of migration occurring over hundreds of thousands of years.
Additionally, the Denisova hominin’s genetic legacy continues to influence the genetic makeup of modern humans today. Research has shown that some present-day populations, particularly those in Asia and Oceania, carry traces of Denisovan DNA. For instance, modern-day Tibetans have a gene variant that is thought to have been inherited from Denisovans, which helps them survive at high altitudes. This further highlights the lasting impact of these ancient human populations on modern genetics and provides valuable insights into how ancient humans adapted to different environments.
One of the most fascinating aspects of the discovery of the Denisova hominin is the way it highlights the dynamic and interconnected nature of human evolution. While the discovery of the Denisovan lineage adds another layer to the complexity of human migration, it also emphasizes the extent to which different human species may have interacted, shared genetic material, and influenced one another. The idea that ancient humans, such as the Denisovans, Neanderthals, and Homo sapiens, might have coexisted in certain regions and exchanged genes is not new. In fact, it was already established that Neanderthals and modern humans interbred in Europe and Asia. However, the discovery of the Denisova hominin pushes the boundaries of this idea even further and demonstrates that human evolution was not a linear progression, but rather a web of interwoven populations that existed and evolved simultaneously.
The genetic evidence gathered from the Denisova Cave is also helping scientists re-evaluate the role of environmental factors in shaping human evolution. The Altai Mountains, where the Denisova hominin lived, are known for their harsh and extreme climates, which would have presented significant challenges for early human populations. The Denisovans likely had to adapt to these conditions in unique ways, which could explain some of their distinct genetic traits. Understanding these adaptations may provide valuable insights into the resilience and flexibility of human populations as they faced changing climates, landscapes, and ecological pressures.
More information: Johannes Krause, Qiaomei Fu, Jeffrey M. Good, Bence Viola, Michael V. Shunkov, Anatoli P. Derevianko & Svante Pääbo, The complete mitochondrial DNA genome of an unknown hominin from southern Siberia. Nature, 24 March 2010, DOI: 10.1038/nature08976