"You were suggesting in your original post that Muhammad is the ancestor of everyone on Earth, basically. That implies that everyone else who lived in his time was a genetic dead end."

No, in the article I linked to it said Muhammad is ancestor to everyone in the West- not the world. And I don't see how you get idea that eveyone else was a genetic dead end- quite the contrary, most of the people in the world at that time would also have similar numbers of descendents and given enough time everyone in the world will be their descendents.

"Do you see the similarity in these statements? You basically made a Darwinian conjecture, that nature selected Muhammad's descendents to dominate the earth (which I think is BS). What are your reasons for believing Muhammad is the ancestor of everybody? Why not Joe Blow who lived next door to him?"

No one here said "Muhammad's descendents to dominate the earth". Nor the West.
And it also probably includes Joe Blow who lived next door- and all goat herders and camel jockeys within thousands of miles.