If I'm understanding what you're saying correctly:
People have a common marker up to that point, which was first found in one of our ancestors in a region of Africa. Meaning that we share a common ancestor who lived in Africa.
Past that, are you saying Humans did not interbreed with other sub-species[after the dispersal] or are you saying that the interbreeding didn't happen before the marker was 'inserted' otherwise we'd have humans without the marker?
" You may share some neanderthal characteristics from the common ancestor before the human branch evolved (as we do with homo erectus, chimps and bonobos), but it's impossible that the neanderthal is your ancestor bypassing the african homo sapien (which I think you are arguing)."
Need to know if this is saying that your/his/my ancestors all merge to that point[as indicated by the marker] and therefore there is no branch of humanity that skipped this person and developed out of another sub-species.
Or
Are you saying that Humans did not mate with Neanderthalls and other sub-species at all/in a significant way before or after the long march out of Africa?
There is no branch of humans who don't have the L1 marker (the marker at position 4312 of the mitochondria) - they've been testing all over the world and haven't found a single one. So there are no people who have skipped the original human "eve" from africa.
And Neanderthals don't have that marker - remember they evolved and left Africa 350,000 years ago, a full 160,000 years
before the first human appears - our species is only 190,000 years old. And they would have been continuing to diverge from us during the whole of that time.
This about the following simple experiment. Say you meet a neanderthal woman and fancy her and have a baby with her. The mitochondria of her children will come from her, and will
not have that L1 marker. And if her daughters had children, they'd pass on mitochondria without that marker too, and so on down time.
So if humans and neanderthals mated there'd be some people without that marker - but they haven't been found yet. You can do a similar experiment with the Y chromosome and a Neanderthal man.
The other thing is how Neanderthals survived 300,000 years in Europe and Asia through some pretty dramatic climate changes - but got wiped out very quickly in both regions when humans encroached in their areas. People are reluctant to believe we hurt such a closely related homonoid - but we must have done something. Species don't just disappear without reason.
The whole origins of humans thing may seem confusing because there
are differences between human races - but that's primarily down to epigenetics (tags on our genes that switch on and off depending on environment, climate, quality and quantity of food).
We're continuing to evolve through epigenetics right now mostly in minor ways, though there's some horrible evidence coming out that test-tube babies have a statistically higher incidence of genes turning off leading to hideous diseases because the sperm and egg are interpreting the petridish as a hostile environment (as compared to the safety of the womb).
And then of course natural selection plays a part too - some people survive and some people don't, sometimes through environmental bad luck, but often through choices and decisions and their brains or lack of them.
Here's an example: The Greenland Norse died out completely but the Greenland Innuit didn't due to differing practices in food gathering (for some unknown reason the Greenland Norse refused to fish despite being surrounded by the richest fishing waters in the world). But now the Greenland Innuit are dying - because they primarily eat ocean fish, they're being poisoned by all the heavy metals that are being dumped in the seas, whereas those of us eating regulated food grown on land are safe. They're in a quandry, they can't grow anything on Greenland because the land is too poor and cold and won't support farming (the reason the Norse died), and there's no industry they can set up to enable them to earn to buy food from elsewhere, without damaging the ice sheet - so should they abandon Greenland in order to change their diet? Where would they go?
The whole evolution thing is fascinating. We're essentially all the descendants of successful survivors and some of that success is down to usurping other species like the Neanderthals and chasing them away from the best hunting and farming grounds.
