Let me now briefly retrace the argument about human equality and the significance of birth. It is comprised of two main stages. I first stated an argument for a basic threshold beyond which the differences between the cognitive or emotional capacities holding between human beings are not to be recognized for most purposes. It is morally critical that there is a point beyond which personhood, in its extra-legal and legal sense, is absolute.
I next presented an argument about what that threshold ought to be. I first pointed out that within an acceptable range of thresholds, the law’s interest in resolution by stipulation means that the only applicable standard in picking an exact threshold is that there is no conclusive reason against settling upon it. However, I argued that there is particularly good reason to place that minimum threshold at birth, owing to the significance of separate physical embodiment for cultivating the core constitutive properties of personhood. Birth is a cataclysmic event in the life of a new human being because it propels the fetus into the context in which it can begin learning how to act in the world and be brought into membership with other human beings. Because of this, I contested the widely held belief that birth is a trivial, merely circumstantial change.
The range property analysis of personhood does not demand total blindness to variations in capacities between different human beings. We might, for instance, acknowledge that it is not in the best interests of a permanently comatose patient to have his life artificially prolonged, given that there are such significant elements of human life that he can no longer realize. It stated only that relative to the property of being a person, all living human beings post-birth are to be treated as equal within the range. Conversely, treating personhood as a range property from birth does not demand blindness to the similarities between late fetuses and neonates, which remain very close to one another on the continuum of human development. It may well be appropriate to respond to this closeness by according the late fetus a degree of moral standing, as the gradualist thesis holds. However, the closeness of late fetuses to neonates on the developmental scale is not an objection to the birth threshold. Both the moral interest driving the need to stipulate that threshold and the case for tying it to birth are unaffected by the many resemblances between early human beings either side of birth.