Neanders and Denisovans are different from us "modern" (African) humans, going back maybe 700k years. It was found that later specimens of both, which are the best-preserved, are mitochondrially African. That is: there was an out-of-Africa movement, after 370 kya but long before us (70 kya), whose female line pushed out the native Eurasian line.
Martin Pitr's team finds that the same is true for the Y chromosome - the men. There were male-Neander (or -Denny) + female-African hybrids; and female-Neander + male-African hybrids. When the hybrids met, their offspring were of course half of each; but the grandkids with the advantage were male-African and female-African. Eurasia ended up still Neander and Denisovan, but tracing their direct ancestry on both sides back to Africa. An analogy in our subspecies is how Sundaland men pushed out the native lineages of pre-Aurignacian / -Magnon Europe. (The Indo-Europeans are different, they just invited everyone to the Number Six Dance.)
The paper thinks that Eurasian DNA had broken down, such that their Y-chromosomes and mitochondria had the disadvantage over Africans'. I suppose because the population never got over a few thousands. And the distances were so vast and impassable that Neanders and Denisovans didn't cross each others' paths much.
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