Modal Properties, Moral Status, and Identity

In his essay, “Modal Properties, Moral Status, and Identity,” David S. Oderberg answers the objections that have been raised against the Identity thesis, the claim that the zygote and the embryo are individual human beings. He concentrates on the cluster of objections that are based on certain biological phenomenal and appeal to the modal properties of the zygote and the embryo—to what could happen to the immature human being in certain circumstances.

Here’s Oderberg’s explanation of the embryological terms:

The term 'embryo' comes from the Greek for 'to grow,' and simply means 'growing human being'; and 'foetus' comes from the Latin for 'young offspring.' Hence either term could properly be used to denote the human being at any stage of development. 'Zygote,' 'morula,' and 'blastocyst,' on the other hand, denote specifically cellular aspects of the early human-the first coming from the Greek for 'yoke,' and signifying the coming together of the gametes, the second from the Latin for 'mulberry' and signifying the shape of the cellular matter, and the third from the Greek for 'sprout' and 'bladder,' signifying the hollowing out of the cellular matter constituting the human being at this early stage. 

According to Oderberg, the status of the zygote and the embryo can only be understood when there is a proper grasp of the metaphysics of human identity and there is a determination to keep morality at the top of the scientific agenda. He argues that life starts at the stage of conception itself. Here’s an excerpt:

Conception is that event, typically involving the union of sperm and egg, which consists in a change in the intrinsic nature of a cell or group of cells, where that change confers on the cell (or its descendants in the case of division) the intrinsic potential to develop, given the right extrinsic factors, into a mature human being. Note that the concept of intrinsic potential employed here is not the same as that rejected earlier when discussing whether the zygote is a potential human being. It was claimed that the zygote is an actual human being, but the definition of conception just given appeals to the idea that it is an actual human being with the potential to develop into a mature member of its kind, as long as circumstances permit it. The intrinsic potential mentioned in the definition is, therefore, a property of its actual humanity. We can see that this definition excludes the possibility that the egg is a human being, since its nature would have to change; without that change, it does not have the intrinsic potential to develop into a mature human being. The definition includes the union of sperm and egg, however, since there is an intrinsic change of nature. Whether this change is in the sperm or the egg is irrelevant for metaphysical purposes—it could be the egg which is changed by the sperm, or vice versa. As a matter of brute biological fact, however, the sperm-egg union is best conceived of as a change in the egg: the sperm enters it from outside, disintegrates, and the nucleus in its head merges with the nucleus of the egg. The definition also includes parthenogenetic cells and cloned cells, both of which have undergone an intrinsic change of nature from mere gametes, somatic cells or whatever, to cells with the intrinsic potential, given the right environment, to develop into mature human beings. If one of these cells only develops for, say a few days and the embryo then dies, this is not because the cell lacks the intrinsic potential to develop into a baby, child, or adult, but because certain extrinsic factors are not present, such as important nutrients; and this is indeed the currently proposed biological explanation of why full development fails in the case of cloned or parthenogenetically generated nonhuman animals. 

Oderberg defines conception as the coming into existence of a human being, but if this is the case then the zygote has the moral status of a human being.