quote:
While such an individual may have existed, I don't see why it is at all necessary or even reasonable to assume she did. What defines one as human vs. chimp is not locked away in a single gene. T
In fact Dr. A did give reasons why it IS necessary. Provided the divisions between the gorilla and human/bonobo/chimp lineages and the human and bonobo/chimp lineages are clean it must be the case.
To repeat the explanation in my words. Start with a common ancestor of living humans and bonobos/chimps from the ancestral population after the split with the gorilla lineage is complete. This individual (by definition) must have both human and bonobo/chimp descendants.
Either this individual has a child which also has both human and bonobo/chimp descendants or it does not. If it has such a child we move on to that child and repeat, at each stage choosing a child with both human and bonobo/chimp descendants.
Since we know that the lineages have diverged this process cannot go on forever. Therefore at some point we must find an individual who has human descendants and bonobo/chimp descendants, but no child with both human and bonobo/chimp descendants.
It follows that this individual must have at least one child with human descendants and no bonobo/chimp descendants and at least one child with bonobo/chimp descendants but no human descendants.
Therefore Doctor Adequate is correct