Animatio
The onset of individual human life has fascinated thinkers of all cultures and epochs and the history of their ideas may shed light on an unsettled debate. Aristotle attributed three different souls to subsequent developmental stages. The last, rational soul, was associated with the formed fetus, and entailed fetal movements. With some modifications, the concept of delayed ensoulment—at 30, 42, 60, or 90 days after conception—was adopted by several Christian church fathers and remained valid throughout the Middle Ages. During the Enlightenment, philosophers began to replace the rational soul by the term personhood, basing the latter on self-awareness. Biological reality suggests that personhood accrues slowly, not at a specific date during gestation. Requirements for personhood are present in the embryo, but not in the pre-embryo before implantation: anatomic substrate; no more totipotent cells; and decreased rate of spontaneous loss. But biological facts alone cannot determine the embryo’s moral status. Societies must negotiate and decide on the extent of protection of unborn humans. In the 21st century, fertilization, implantation, extrauterine viability, and birth have become landmarks of change in ontological status.