In the comment thread to the last post, Joseph Bolin gives a lovely distinction that harmonizes the scientific opinion on monogenism with a Christian claim to monogenism. The distinction has the added benefit of resolving the the tension by showing that it arises from assuming something unnecessary to monogenism.
Monogenism means that all persons now living share a common ancestor. As applied to Christianity, monogenism is the claim that all potential Christians (all persons on earth from the first century until now) have a single common male ancestor. To assume that this single ancestor was at some point the only person in existence is an additional and unnecessary assumption. My cousin and I are of one family through our grandfather, which would be true whether our grandfather was the only person who existed or not; in the same way, Christian monogenism requires that all persons be cousins through some common male ancestor, regardless of whether this ancestor was the only person who existed. The present findings of genetics make it unlikely that a common male ancestor was the only person who existed, but whether he was or not has no effect on the truth of monogenism. Deciding that we all have one ancestor does not decide if this ancestor was part of a larger population or not.
The confusion over monogenism arises from a classic sophistry: mixing up the senses of a word. The prefix “mono” often indicates that there is one and only one thing to which the word is prefixed: monotheism means there is one and only one God; monotone speech is speech in one and only one tone; monochrome color schemes mean there is one and only one color; but monogenism does not mean that there is one and only one common ancestor, still less that this one ancestor was at some point the only person to exist.
As it turns out, there is good reason to believe that there is at least one common male ancestor of all human beings, even though there is no reason why we should judge that this individual was the biblical Adam-sc. that single male anscestor through whom we are all called to a good higher than nature, and through whose sin we failed to attain the economy of grace. Notice that the “Y-Chromosome Adam” is an individual who, in addition to being a common ancestor of all human beings, has had at least one male progeny in his line in every generation that followed. The biblical Adam and the Y chromosome Adam need not be the same person- and in fact the Y-chromosome Adam was less likely to occur than the biblical Adam.