April 10th, 2018
(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: email@example.com
As soon as the Denisovan were discovered, it should have become necessary to update our ideas about where homo sapiens first arose. It’s simply too much of a coincidence. Neanderthals and Denisovans and Sapiens seem more similar to each other than to homo erectus, therefore they must have had a somewhat recent common ancestor, and if Neanderthal and Denisovans first evolved in Asia, that means Sapiens must have evolved there too. Roughly, the most likely theory at the moment is:
1.) homo erectus evolves in Africa 1.8 million years ago
2.) homo erectus leaves Africa 1 million years ago
3.) some homo erectus wander off and become the common ancestor of Neanderthals and Denisovans. You could call this wayward tribe ND, or you could call them homo heidelbergensis. I doubt the debate between the lumpers and splitters will ever be resolved. I used to read a lot of Ian Tatersall, who is a famous splitter. He goes so far as to claim there were once 23 human species. The extreme lumpers, of course, insist that everything was homo erectus, all the time, till we show up, maybe making an exception for Neanderthals, but maybe not even them. It doesn’t matter. Call the tribe the ND tribe of homo erectus, or call them homo heidelbergensis. They give rise to Neanderthals and Denisovans.
4.) some of the ND or homo heidelbergensis head south and interbreed with homo erectus. Depending how you look at them, you can see them as very stupid Neanderthals, or very smart homo erectus. They are us, homo sapiens.
With the recent announcement that the 260,000-year-old Dali Skull in China is that of an archaic Homo sapiens, and Levallois type stone tools (usually associated with these archaic Homo sapiens) in India date to 385,000 years ago, the case for an Asiatic genesis of our species has strengthened incredibly. The only thing missing here is direct evidence that early Homo sapiens migrated into Africa, surely that would be the final proof?
In September 2017, a team of scientists from Buffalo University announced that they had made an astonishing discovery while investigating a saliva protein in humans, designated as MUC7. The team realised that a significant number of Sub-Saharan Africans carried a wildly different variant of the MUC7 gene to members of all other sampled populations, suggesting to them that the ancestors of these people had interbred with another ancient human species. The date for this interbreeding appeared to be around 200,000 to 150,000 years ago, and the hominin species responsible was calculated to have diverged from our direct ancestors between 1.5 to 2 million years ago.
The dates suggested in the MUC7 study are nothing short of incredible, on the one hand, we have a date close to the first clear expansion of early modern humans across Africa, and on the other hand, we have a date range that meshes well with the divergence of Homo erectus from Homo ergaster.
“This unknown human relative could be a species that has been discovered, such as a subspecies of Homo erectus, or an undiscovered hominin. We call it a ‘ghost’ species because we don’t have the fossils.” – Omer Gokcumen, assistant professor of biological sciences, Buffalo University
The scientists also realised that non-African modern humans carried a variant of MUC7 that was much the same as that carried by Neanderthals and Denisovans, both of which are accepted as Eurasian archaic hominins. Somehow the scientists failed to make the final leap towards the most obvious conclusion.
If Homo sapiens evolved in Eurasia, alongside Neanderthals and Denisovans, from an Asian Homo erectus last common ancestor resident there, it would be no surprise they all carried a similar MUC7 gene. As some groups of early modern humans migrated into Africa around 200,000 years ago, they would have inevitably encountered any descendants of Homo ergaster, perhaps hominins like the species Homo naledi, known to have inhabited South Africa until at least 236,000 years ago. The fact that the modified version of MUC7 is common across Africa also suggests it entered the human genome almost as soon as the first population of Homo sapiens appeared in Africa before they split into separate regional groups.