One question asked repeatedly in the history of Christology is the following: given that the incarnation was God’ s chosen method of redeeming us, why did God become human by the cooperation of the Blessed Virgin Mary? Why not just create a human body and soul ex nihilo and simultaneously with that creation have God the Son assume this new instance of human nature? In answer, Augustine for instance argues that the latter option would have been a legitimate means of (...) incarnation, but that it was not as fitting as the method actually employed. Aquinas agrees. By contrast, John of Damascus seems to think that the ex nihilo option would not have constituted a genuine assumption of human nature, such that redemption required the cooperation of the Theotokos. I argue that insights provided by contemporary biology support St. John’s perspective, insofar as modern biological taxonomy suggests that lineal descent is a necessary condition for belonging to a species. As such, to take on a genuinely human nature God had to enter into the existing human lineage; creating a new ‘human’ body and soul ex nihilo would not have sufficed. (shrink)