I mentioned the other day that a small amount of Neanderthal genes have been detected among non-African modern humans in a homogeneous way that strongly suggests it happened only within the process of migration into Eurasia and beyond.
The percentage of Neanderthal "blood" in non-Africans is estimated in 1-4% (average: 2.5%) what means the equivalent to one great-great-great-grandparent (3.13%) or great-great-great-great-grandparent (1.56%). In other words: the equivalent to one of 32-64 ancestors.
The homogeneity of the apportion across people of Eurasian ancestry (includes Oceanian and American natives) tells us that this was the situation in the Migrant Population at the arrival to South Asia, where it expanded very dynamically.
We must understand that, due to various environmental reasons (adaptation to warm climate, arid barriers and Neanderthal pressure) the Migrant Population must have been rather small between Africa and South Asia. At least that's what the genetic signature strongly suggests. However it was not too small or not too homogeneous because several lineages (2-3 at least per gender) arrived to the South Asian secondary cradle (a really small homogeneous population would surely have got its lineages more strictly fixated, i.e. one per gender).
There are many different detailed scenarios that could explain this limited gene flow but the following one is which seems to me as the simplest one on light of the available genetic and archaeological data:
Feel free to discuss, of course, it's very tentative and pretty much open to variants and alternatives.
Why did I get the main migrant population go via South Arabia? Because there are many clues that suggest so but it's again a personal choice: my best hunch.
Why did I place the main admixture event in Palestine? Because there's some archaeological evidence telling of at least contact between both species there c. 130,000 years ago (old stratigraphic date). But could have happened in many other areas of the Middle East, in Iran for instance (in which case, we could consider a single migrating population via South Arabia and consider the Palestinian episode genetically unproductive).
Just trying to figure out...