Here’s a story about human evolution, and about how different human species have given us genes that allowed us to thrive in particular conditions.
The study of ancient DNA has allowed scientists to figure out that two different human species that co-existed with Homo Sapiens interbread with us and passed along some of their genetic material. Unless you and all your ancestors come from sub-Saharan Africa, for instance, your genetic code has a bit over 2% Neanderthal. And it turns out, that 2% likely contains genes that help with immune responses. Called “Toll-like receptor (TLR) Genes 1, 6, and 10,” they help cells respond to many bacterial, fungal, and parasitic invaders. Homo Neanderthal lived in colder climates than modern Homo Sapiens for well over 100,000 years, so it makes sense that they had adapted their immune systems to those areas. By the time Homo Sapiens left the African continent and started mixing with our cousin population, these TLR genes would have given us a survival advantage, which is why those genes have remained such a stable part of our own DNA until now.
In 2010, scientists discovered another human species that lived alongside us Homo Sapiens, called Denisovans. And, just like with Homo Neanderthals, the DNA of Denisovans has been found in many modern human groups. Definitely less widespread than Neanderthals, the Denisovans nonetheless also imparted their genes to the advantage of some Homo Sapiens– in this case, the Tibetian peoples. In a study from 2021, scientists analyzed the Tibetan and Denisovan genomes and found that both groups have a gene called EPAS1, which helps to transport oxygen in the blood in a way that counteracts the condition of hypoxia that many people experience at high elevations. Although these scientists haven’t completely hammered out the timeline of Tibetans and Denisovan mixture yet, they know that there were two different eras when these groups did meet, and have children together, and the modern humans positively selected the altitude-adapting gene EPAS1.
The images show modern Homo Sapiens next to their cousin species, with a Neanderthal skull and a computer simulation of a Denisovan.
Source(s): This information was covered in _Remnants of Ancient Life: the New Science of Old Fossils, by Dale Greenway, 2023 (Princeton UP); Neanderthal skull wikicommons. Image of modern homo sapiens from https://www.dailymail.co.uk/sciencetech/article-3569545/amp/The-founding-fathers-Europe-DNA-reveals-Europeans-related-group-lived-Belgium-35-000-years-ago.html. Image of Tibetian man from “Tibetian people”, _Atlas of Humanity_. Image of Denisovian from Maayan Havel, BBC, “Denisovans:face of long-lost relative unveiled”; Peiqi Zhang et al, Denisovians and Homo sapiens on the Tibetian Plateau: dispersal and adaptations, _Trends in Ecology and Evolution, Dec 2021; 37(3): 257-267. _American Journal of Human Genetics_ Deschamps et al.: “Genomic Signatures of Selective Pressures and Introgression from Archaic Hominins at Human Innate Immunity Genes” cited in _Institut Pasteur_ “Neanderthal genes gave modern humans and Immunity boost, allergies” 2016, Jan 8.
