Modern humans carry genetic traces from now-extinct human relatives, such as Neanderthals and Denisovans, as shown by numerous scientific studies. Non-African populations have between 1.8% and 4% of their DNA from Neanderthals, a result of interbreeding that likely took place 50,000 to 60,000 years ago, possibly in the Middle East. In contrast, people from Sub-Saharan Africa have almost no Neanderthal DNA, while Melanesians, a population group in the Pacific, have 5 to 6% Denisovan DNA. Recent research has refined these estimates, with some studies suggesting the Neanderthal DNA range is between 1.8% and 2.6%, while others note that it can go as high as 4%, depending on the population. This research is largely attributed to Svante Pääbo, a Swedish scientist at the Max-Planck Institute for Evolutionary Anthropology, who sequenced the first complete Neanderthal genome in 2010. This achievement earned him the Nobel Prize in Medicine in 2022. The Neanderthal reference genome used in these studies comes from bones found in the Vindija cave in Croatia, which belonged to three Neanderthal females. Evidence that interbreeding happened long ago comes from the genome of a 45,000-year-old Homo sapiens found in western Siberia, which already contained segments of Neanderthal DNA. Additionally, the genome of a Neanderthal woman from the Altai region in Siberia showed that her parents were half-siblings, suggesting a high level of inbreeding within small, isolated groups. In contrast, the genome of a 34,000-year-old Homo sapiens found near Moscow, at Sungir, shows less inbreeding, indicating more extensive social networks and interactions between different human groups at that time. Some of the genes inherited from Neanderthals continue to influence human traits today, including immunity, blood clotting, and even susceptibility to severe forms of COVID-19. A 2021 study in the journal PNAS found a Neanderthal-derived gene linked to better resistance to severe cases of the virus. A large 2016 study in Science, based on the medical records of over 28,000 patients, found that Neanderthal DNA is associated with a wide range of modern traits, from a higher risk of depression and blood clotting disorders to skin conditions like actinic keratosis, which are caused by sun exposure. Interestingly, these skin conditions may have been beneficial for Neanderthals living in regions with less sunlight, as they could help in vitamin D production. Some Neanderthal DNA variants are even linked to nicotine dependence, and other research has found that they influence traits such as skin and hair color, height, sleep patterns, and mood. If you are of Sub-Saharan African descent, your genome is likely almost entirely free of Neanderthal and Denisovan DNA. This is due to geography rather than genetics: the ancestors of Sub-Saharan populations never left Africa before the major migration that led to interbreeding with Neanderthals and Denisovans, who were living in Europe and Asia. Only the groups that left Africa had the opportunity to intermingle with these archaic humans, which is why the genetic traces of Neanderthals and Denisovans are found mainly in today's European and Asian populations. This uneven distribution of ancient DNA is valuable to scientists, as it helps them reconstruct the migration routes of early humans and the points where different human groups met. Each piece of archaic DNA found in a modern person acts like a time marker, helping researchers determine where and when these ancient encounters occurred.