Steve, who also lives around the same time, will also become the progenitor of all of humanity. So will Alex, also part of the same generation as Steve and Bob. And James, and Peter, and Ezra, and all sorts of other people.
No, Bob's genes will never become part of Alex's genes, unless Alex's descendant's mate with Bob's descendant's. Your scenario works only when there are less than a population of 50 or so. Once the population increases beyond this - any mutation that occurs in one lineage will NEVER become set in the population.
This is what you're missing - while there is just one most recent human common ancestor, there are a very large number of universal human common ancestors. It's not that one pair is the sole ancestor of every human alive so much that the family tree is incestuous to the point where a great many pairs necessarily must have been directly ancestral to every human alive today. Indeed, for the people living something like 5,000 years ago, they necessarily belong to at least one of these three groups:
A) The direct ancestor of every human alive today
B) The direct ancestor of no human alive today
C) A member of an extremely isolated group
This is what you are missing - that there can be no large numbers of universal ancestors. If the population is large - Bob's genes will never become part of the general population. Bob's descendants will never mate with the entire population to spread his genes to them, if the population starts with greater than 50 individuals.
Indeed, for people living 5,000 years ago there is no sense discussing it since they became extinct during the flood and the population started from 8 individuals - which is why all humans share a common genetic lineage (beyond that of Adam and Eve) - the only differences are the variations possible within the genome for each distinct group as they began to migrate and became isolated.
You know - all Asians remain Asian - despite the variations within that breed. All Africans remain African - despite the variations within that breed. Only when Asian mates with African does a new breed come into existence. There is no purpose at all to speculate anything different - since we have never observed anything different. The empirical evidence shows you that all is in stasis until breed mates with breed and produces that variation. This is what is wrong with your entire classification system of the fossil record. You list every fossil found that is slightly different as a separate species - despite the empirical evidence that variations within a species are merely different breeds. There is no other observations of the natural world that fit any other interpretation.
These are NOT separate species, they are different breeds of the same species:
And as actual study of bone growth in fossils also showed you they classified
babies and adults of the same species incorrectly.
You are basing all of your assumptions on the incorrect classification of the fossil record - including
incorrectly classifying human ancestors.
Have you even bothered to study the science of bone growth? Has any paleontologist except Jack Horner actually cut apart those precious bones to study them? No, you just continue with the same beliefs already falsified because you don't want to consider the truth, that 80% of the fossil record has been incorrectly classified all in their rush to get their names in the books as the discoverer of a new species.
And we have yet to apply the observational fact of breeds within a species - raising that number from 80% to 98%. This is also why you run from discussing those Finches - because you know I am right. That they rushed to get their names in the books as the discoverer of a new species and in an attempt to prove speciation. When the direct empirical evidence should tell you they are all merely different breeds of the same species. Interbreeding and producing fertile offspring since the moment they arrived on the islands. Speciation never occurred - just what we observe empirically in the natural world - breed mating with breed producing new breeds within the species.