Nature reports on recent DNA studies which suggest that AMH – Neanderthal encounters took place also in Europe around 40, 000 years ago.
It seems reasonable to assume that encounters began in central Asia / Middle East perhaps as early as 50-60,000 years ago and then moved westwards. AMH and Neanderthals could have coexisted at particular locations for as long as 5,000 years (250 generations) and it is more likely that Neanderthal populations declined as their habitat was encroached upon and taken over by the expanding AMH population. Not an intense war or even an intentional genocide of the Neanderthals but a gradual takeover of their territories as Neanderthals were pushed westwards and finally died out in Iberia some 30,000 years ago.
So I imagine bands of AMH and Neanderthals living in close proximity but largely with each group keeping to itself. When they encountered each other no doubt conflict occurred and the victors took spoils. For whatever reasons, AMH “won” the majority of these clashes and their territory grew while that of the Neanderthals shrank – westwards across central Asia and Europe. And in these clashes it is my speculation that the victors took the females of the vanquished as part of their spoils. Most probably AMH females joined Neanderthal bands and Neanderthal females joined AMH bands as spoils of war. But only the offspring of the Neanderthal females have left their mark because they had joined the line that would continue:
…. DNA analysis of a jawbone from a Romanian cave from about 40,000 years ago had a Neanderthal for a great-great- grandparent.
I take this grandparent to be a Neanderthal grandmother who was abducted by some marauding group of promiscuous humans only because the ensuing child survived to give rise to us and it is the human environment which has continued. The picture I have is that our Neanderthal genes today are due mostly to the Neanderthal females who were “impressed” into service by an aggressive and expanding human population. There may well have been Neanderthal male – human female offspring but they would more likely have been brought up in a Neanderthal environment, which – along with them -has not survived.
So I imagine the decline of the Neanderthals taking some 20-30,000 years as AMH expanded westwards and the decline of the Denisovans probably starting a little later but taking somewhat less time. The encounters and admixing probably only occurred with the tribes and bands at the frontiers.
Maybe the DNA analyses will someday be sophisticated enough to be able to distinguish if it was mainly Neanderthal females who have contributed to the current AMH gene pool or not.
But until then my story is that it was the Neanderthal females taken as spoils of war by expanding AMH tribes who have provided the majority of our Neanderthal genes.