In Defense of Stem Cell Chimeras: A Response to "Crossing Species Boundaries"

Jason Scott Robert and Françoise Baylis's (2003) evaluation of chimera experiments demonstrates that biological species are not objective enough to inform normative content. Perhaps a protracted discussion could have been avoided by recalling the historical conception of species, one that is more akin to the common-sense categorization eventually suggested by Robert and Baylis's. Instead of invoking contemporary scientific and philosophical notions, we should consider why and how species themselves were proposed in the first place.

Linnaeus, father of biological taxonomy, originally grouped species by their appearance. Though his was the first attempt at systematic biological categorization, it is likely that Linnaeus adopted a similar common-sense approach as was, and is, used by many human societies.In effect, the very recognition of biological categories seems to arise from our ascribing significance to an organism's visible appearances, functions, or behaviors to indicate where boundaries should be drawn (de Sousa 1984). As such, these categories will never satisfy ontological requirements but will only reflect individual desires for such ontological categories. Robert and Baylis seem to desire the validation of species categories very much. However, biology, as with all sciences, is a methodology whose pursuit does not aspire toward these lofty aims. Genetic similarity or reproductive criteria used to describe species do not reveal real categories but are instead theoretical tools used to generate predictions and further empirical scientific advances (de Sousa 1980). At the outset it would seem apparent that biological species are a red herring.

I suggest the morality of human chimerism is more simple. We should begin by asking how human-nonhuman hybridization experiments differ from other forms of nonhuman research. We, as human beings, value organisms because either:

1. they are visible and we have become accustomed to them in our and our ancestors' environments; or
2. because they possess capacities or characteristics that remind us of our own humanness.

As Robert and Baylis note, it is the potential alteration of nonhuman moral value (which I use here in a loose sense) that could be ethically problematic. Human appearances are symbolic of our humanity, and human capacities are components of our humanity, so it follows that at least some moral obligation should be associated with these. It is perhaps a facet of morality that higher moral status will inevitably be ascribed to entities that possess recognizable human features. This has proven true, as the ethicality of research involving nonhuman primates has changed with the recognition that they possess some capacities similar to human capacities. The more fully an animal meets our "humanness," in its visibility or its evident behaviors, the more it is valued, because we infer that it possesses capacities that are owed moral obligations. I believe that in initiating a discussion of species boundaries Robert and Baylis have completely missed the point of why and whether human-nonhuman chimeras are morally wrong. Chimeras are not controversial in that they cross actual or theoretical categories but in that they could possess functions that are necessarily associated with moral worth.

Were a human being to be infected by an invisible retrovirus that inserted its functional DNA into the human's genome, we would not see the virus or its functions, and we would clearly continue to recognize the individual as only human. The false notion that genetics determines personhood is an obvious point. The intermingling of genetic dissimilarity will not be the cause of controversy that might soon surround stem cell chimeras. For instance, a gene called Pax6 is critical for eye development, even to the point that a fruit fly's Pax6 gene can induce the formation of an eye in the distantly related frog (Onuma et al. 2002). But this does not result in a fruit-fly eye growing out of a frog's body; rather it is the host frog that directs the use of this gene to produce a...