Thomas Aquinas held a particularly complicated version of this consensus position.

For him the first substance independent of the mother is the embryo living a plant life with a vegetative soul. This vegetable substance disappears and is succeeded by a substance with an animal soul, capable of nutrition and sensation. Only at an advanced stage is the rational soul infused by God, turning this animal into a human being. The whole process of development is supervised by the father's semen, which, according to Aquinas, remained present and active throughout the first forty days of pregnancy. For this biological narrative Aquinas claimed the authority of Aristotle. According to Jones, however, Aquinas was not only seriously in error about the biological facts, but had also misunderstood Aristotle (who should, he says, be counted among the supporters of the view that human life begins at conception). At this distance of time, it is difficult to see why Aquinas's teaching on this topic should be accorded great respect.

Jones's exhaustive study makes it abundantly clear that there is no such thing as the Christian consensus on the timing of the origin of the human individual.

There was, indeed, a consensus among all denominations, until well into the twentieth century, that abortion was sinful, and that late abortion was homicide. There was no agreement about whether early abortion was homicide.

However, those who denied that it was homicide still regarded it as wrong, because it was the destruction of a potential, if not an actual, human individual. There was again no agreement as to whether the wrongfulness of early abortion carried over into the destruction of semen before any conception. Even within the Roman Church, different popes can be cited in support of each option.

The question whether early abortion is homicide was and is important, because if it is not, then the rights and interests of human beings may legitimately be allowed to override the protection that by common consent should in normal circumstances be extended to the early embryo. The preservation of the life of the mother, the fertilization of otherwise barren couples, and the furthering of medical research may all, it could be argued, provide reasons to override the embryo's protected status.

This line of argument was found convincing by the Warnock and Harries Committees.

They made a significant contribution to the debate by offering a new terminus ante quem for the origin of individual human life -one which was much earlier in pregnancy than the forty days set by the pre-Reformation Christian consensus.