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Nick Kapur @nick_kapur
, 12 tweets, 2 min read Read on Twitter
The past 10 years have completely revolutionized our understanding of human origins. The 2008 discovery of the finger bone of a previously unknown hominin in a cave in Siberia changed everything. 1/
We now know that modern humans have genetic material from three separate species of hominin - homo sapiens, neanderthals, and denisovans (the people in that cave). 2/
These three species diverged genetically over 600,000 years ago, and remained separate species for hundreds of thousands of years thereafter - the neanderthals went to western Eurasia, the denisovans went to eastern Asia, and homo sapiens stayed in Africa (for a while). 3/
Finally, after many millennia of divergent evolution, homo sapiens spread out from Africa in two waves, approx. 100,000 and then again 60,000 years ago, and came into contact with its long lost (and now *very* distant) cousins. 4/
At this point, modern genetic analysis tells us that something very interesting happened: homo sapiens had sexual intercourse and successfully reproduced with these other species on precisely three occasions - once with the neanderthals and twice with the denisovans. 5/
Genetics even tells us a bit about *where* this sex happened. Someone had sex with a neanderthal somewhere in the Middle East, someone had sex with a denisovan somewhere in South or Southeast Asia, and someone else did it again in Melanesia. 6/
Today, all human beings except for sub-Saharan Africans have at least some (1%-4%) Neanderthal genes, East Asians have ~0.2% devisonian genes, and Melanesians have ~2-6% devisonian genes. 7/
Some of these genes are pretty cool. Neanderthals gave Eurasians lighter and better insulating skin to help them survive in colder, northern climes, and denisovans gave Tibetans a gene that helps them live at high altitudes without health problems. 8/…
It's amazing to think that as recently as 2010, scientists were still convinced that homo sapiens *never* had sex with other hominins, and before 2008, didn't even know about the denisovans at all! This is basically still breaking news, and new discoveries crop up every month. 9/
But science has not yet answered the greatest mystery - how homo sapiens could live side-by-side with these other species for so many millennia, yet only interbreed with them on exactly three occasions. 10/
Perhaps we had sex with them all the time, but in the vast majority of cases no viable offspring were produced? Or perhaps our notorious tribalism and fear of The Other were already so strong we mostly stayed away? 11/
In any case, very smart people are studying these questions as we speak, so stay tuned! 12/12
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