Developmental Steps and Moral Status

The biological processes around fertilization and early embryonic development are often accorded considerable relevance in ethical debates, making a detailed description of these processes necessary. This descriptive effort, however, is not based on the belief that "the facts speak for themselves." They emphatically do not. In fact, many ethical controversies about the ethics of in vitro fertilization, embryo research, therapeutic cloning, abortion and the like, are less about ethics in the strict sense as they are about expressing divergent interpretations of biology. The marshalling of biological fact to support apodictic statements of moral status involves many, usually unspoken, "bridge principles." These principles involve highly complex notions, such as unity, individuality, potentiality, and continuity. It is a common misconception that these theoretical concepts constitute stable, common—sense notions that are merely applied to biological entities and processes. In actuality, these concepts are themselves given new meanings and qualifications in the very process of using them to make sense of biological facts. Between the realm of ontological categories and the empirical domain of biology, there is a two—way street.

It is often said that "human life begins at fertilization." Strictly speaking, this statement is meaningless. Human life does not begin at any point of the human life cycle; it persists through successive generations. The ethically relevant question to ask is at what stage a human individual is first endowed with important ethical value and correlative rights against harm. The difficulty is that no particular step stands forth as a self—evident developmental marker, both because developmental events that appear as sharp discontinuities turn out to be protracted processes upon closer scrutiny (for instance, fertilization is a process, not an instantaneous event), and because the highlighting of one developmental process over another necessarily involves more or less plausible philosophical assumptions.

Three different concepts of individuality appear to be relevant:

• genomic individuality as established trough fertilization;

• numerical identity, defined once twinning is no longer possible;

• identity of the self, as sustained by a functional central nervous system.

Fertilization is important because it newly connects two parental lineages that were independent until then. The meeting of sperm and oocyte gives rise to a uniquely novel diploid genome that is not subject to further change. It will be the genome of the future person or persons arising from this particular fertilization. This fact is often misinterpreted according to a hylomorphic interpretation of the genome, where the latter becomes the formal cause of the future human being (Mauron). (Hylomorphism is the aristotelian and scholastic teaching that concrete objects, especially living things, result from a combination of form [morphe] and substance [hyle].) This interpretation suggests the notion that fertilization is the single crucial step, since the new genome appears at that point. This interpretation fails, not only because of the inherent conceptual problems of the hylomorphic view, but also because there exist biological facts such as twinning and genetic mosaicism that show that there is little connection between genomic individuality as such and personal identity. Monozygotic or identical twins are separate persons, even though they share "the same" genome, that originated from "the same" fertilization. This shows that genomic individuality does not provide any basis for the most essential property of personal identity, namely numerical identity through time. To be one and same person through changes in one's biography is an essential ingredient of any workable concept of the person, and the biological basis for this property does not originate before gastrulation. In fact, much of the organic singularity and coordinated functioning as one organism (rather than several potential organisms) is established only at that stage.

However, one may want a richer interpretation of this basic criterion of personal identity. Having a biography of one's own is not just being the same individual through time, but also experiencing a continuity of mental states, which is linked to an at least minimally—functioning central nervous system. In fact, nothing is more central to the modern conception of the self than the functional persistence of a central nervous system that provides the material substrate of an individual subjective biography. For this biographical, or subjective, identity, it is difficult to quote a definitive starting point. It is plausible to place it in late pregnancy, when the earliest possibility of a continuing self seems to be given, but there is no absolute certainty in this claim.

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