Why Definitions Matter and Why We May Need One for Embryo-Like Structures

Take human embryo research, for instance.  As you know, research with human embryos is bound to strict (inter)national rules and regulations. These rules aim at safeguarding societally acceptable practices in a field that arouses strong and competing moral views. And (the scope of) their application will depend on whether or not the researched entity qualifies as a human embryo. A brief look across European jurisdictions shows, however, that the human embryo is defined in incommensurable ways. For instance, whereas Spain defines it in terms of its origin, the Netherlands defines it in terms of its developmental potential. The morally itchy consequence? That research with (particular ‘types’ of) human embryos may be severely limited in some jurisdictions, while not requiring the same (or any) level of regulation in others.

For synthetic embryologists, embryo definitions also play an essential role in demarcating the permissibility and scope of their research. But the incommensurability of embryo definitions, combined with the fast-paced development of different types of embryo-like models, is making it more and more difficult for scientists to determine whether, where, and which embryo-like structures would qualify as such. Let us talk about how perplexing that is in jurisdictions that uphold ‘developmental potential’ as sole criterion for embryo qualifications, for instance. Note that contemporary types of embryo-like structures do not possess the entirety of cells required to progress throughout embryonic development, and are unlikely to acquire them in view of the (commendable) scholarly reluctance to create a perfect ‘human embryo replica’. Nevertheless, it has been argued that the indefinite and unquantifiable character of ‘developmental potential’ may still leave imprudent leeway for interpretation. In particular, some scholars claim that there may be no relevant difference between the potential of a skin cell, a pluripotent stem cell, or a zygote, which would (counterintuitively) imply that they would all be due the same legal reverence ; an issue I will return to in a future column.
For now, it suffices to say that, even though this claim remains disputed, it does indicate how difficult it can be to demarcate ‘developmental potential’ in scientifically useful ways. What’s more, doing so becomes especially complicated in view of the growing capacity to tweak with the developmental capacity of embryo-like models. For example, the ability to incorporate ‘suicide genes’ capable of forestalling their development after a certain point, which would, subsequently, also pre-empt their regulation in potential-based jurisdictions.

For scientists working with embryo-like structures, these ambiguities in legal qualifications evoke practical uncertainties about how to conduct their research responsibly. For society, they evoke the moral question whether the law regulates what it should. At the risk of stating the obvious, leaving embryo definitions as they are, may thus not only undermine their purpose, but also open the door to moral ambiguity in research with embryo-like structures.

¹ In Spain, the human embryo is defined as “a phase of embryonic development from the moment in which the fertilized oocyte is found in the uterus of a woman until the beginning of organogenesis, and which ends 56 days from the moment of fertilization, with the exception of the computation of those days in which the development could have been stopped.”
² In the Netherlands, the human embryo is defined as “a cell or cluster of cells with the potential to develop into a human person.”
³ This is the case with SCNT- and non-viable human embryos. SCNT-embryos do not qualify as human embryos under Spanish law; non-viable embryos do not qualify as human embryos under Dutch law.
⁴ For more on this discussion, see the paper and open peer commentary on Stier, M., & Schoene-Seifert, B. (2013), ‘The argument from potentiality in the embryo protection debate: Finally “depotentialized”?’ The American Journal of Bioethics, 13(1), 19-27.