John Wallingford in "Aeon" has an article, Building Embryos, which unfortunately involves a number of historical fictions and philosophical confusions about the subject. Wallingford says:
In the modern debate over abortion, the doctrine that ‘life begins at conception’ is now so constantly repeated that it’s often assumed to have an ancient, perhaps even scriptural origin. It does not.
In fact, in Catholic canon law, the doctrine dates precisely to 12 October 1869, when Pope Pius IX declared excommunication as the penalty for anyone involved in obtaining any abortion. For the nearly 2,000 years that had gone before, however, many Christian thinkers held the embryo to acquire its humanity only gradually. This concept, linked to the ‘animation’ or ‘ensoulment’ of the embryo, arose in laws first set down more than 3,000 years ago that imposed increasingly harsher penalties for causing the loss of a pregnancy as it progressed.
This is entirely muddled. It has never been controversial to claim that 'life begins at conception', because 'conception' has always been the term for the generation of a living thing. What Wallingford is doing is confusing multiple different things. One strand in the tangle is the debate between preformation and epigenesis (which is the immediate context of this passage in the article); another is the contrast between two different accounts of conception, the ancient one in which conception is seen as a sort of cooking process extending through time and the modern one in which conception is seen as the (for practical purposes) near-instantaneous fertilization of egg by sperm; a third is the legal question of when in the calendar one should set the cut-off for murder as opposed to other kinds of homicide and homicide-related crimes. All three of these are completely different matters, and they are jumbled here as if they were the same issue.
Pius IX also did not, contrary to what is claimed, make some massive change in Church doctrine; he removed the dividing line between treating abortion as deserving lesser penalties or greater penalties in canon law. This did not affect any matter of "doctrine"; it was a purely legal decision. It's sometimes thought that one of the motivations in the decision was that biological discoveries in the previous century had made the sharp dividing line previously used look too arbitrary and unsupported, but the point would have been practical, not doctrinal. It is certainly not the case -- which Wallingford seems to imply -- that there was any denial that there is a progressive development in embryos; indeed, it was likely the reverse -- the fact that there was a progressive development made less defensible any sharp line (a point Wallingford himself makes). It also didn't suddenly "reverse" (as Wallingford later claims) any doctrinal point. As far back as we can manage to trace the point one way or another, we can find prohibitions against using any means of abortion at any time in the process; this is what we find in the Didache, in the Church Fathers, in the penitential handbooks, and the like. Whenever theologians talk about the matter at all, they are quite consistent on this particular point. What has changed over time are various penalties under canon law, civil law, criminal law, etc., and the legal classifications that are used to assign those penalties.
Wallingford is also confused about words like 'progressive' and 'gradualist' in the context of talking about 'becoming human', which he confuses with the notion of progressive and gradualism in which there are stages leading up to becoming human. For instance, he calls 'progressive' and 'gradualist' views that actually are not progressive or gradualist about becoming human (which would require that there be a movement from human-ish to less perfectly human to more perfectly human) but instead hold that the embryo or fetus or infant becomes human suddenly, not gradually, after a process. This is, I think, related to his confusion of matters concerned with the preformation/epigenesis controversy with matters concerned with one's account of conception.
What is perhaps most disturbing is that Wallingford doesn't grasp that the most immediate ethical issues are not associated with any of these things he has discussed but with how to treat things that are human or closely linked to humans, in such a way as to uphold human dignity; he seems to have the notion that ethical worries on the subject are all tied to purely arbitrary religious decisions, when in reality they would obviously arise anyway because human embryos are closely linked to human beings by various continuities, even on the gerrymandering assumption that they should not be considered themselves 'human'. That assumption might change assessments of seriousness or urgency, but it does not in fact eliminate most of the ethical questions, because there is no way to deal with embryos that does not at least imply things about the moral value of human beings.
