SHEEFs, Sentience, and the 14-Day Rule

March 31, 2017

by Professor Bonnie Steinbock 

Embryo research, made possible by IVF, raised the question of the moral status of human embryos. Are human embryos human subjects, who are entitled to stringent protections? Or are they clumps of cells that can be used in research, so long as the permission of their creators is obtained?

Various commissions (Ethics Advisory Board, 1979; Warnock Commission, 1984; National Institutes of Health, 1994) considered this issue, and all arrived at a similar conclusion. Embryos are neither persons nor mere tissue, but a very early form of human life and, as such, entitled to special respect. Specifically, they all agreed on the 14-day rule, which specifies that experiments with human embryos must not let them develop beyond 14 days.

Fourteen days is when the primitive streak (PS), the precursor of the spine and nervous system, appears. This is important because of the connection between the nervous system and sentience, the ability to experience pain or pleasure. Sentience is regarded as morally relevant because causing pain is, in general, wrong. Kicking a can down the road is perfectly permissible, but it would be very wrong to do the same to a sentient guinea pig. On a sentience criterion, nonsentient beings do not have the moral standing that sentient beings do, and research on nonsentient embryos is morally acceptable.

Some argue that what makes it wrong to kill an embryo has nothing to do with sentience. Rather, the embryo is the earliest stage of a unique human being. If it would be wrong to kill a developed human, it is equally wrong to kill that same human being in its earliest stages. However, this raises what is known as the twinning problem. Prior to the appearance of the PS, the embryo can still split into two (or even more) embryos, each giving rise to a separate individual -- (monozygotic) twins. However, since the twins are not the same individual, then neither twin can be uniquely identified with the original embryo, since it gave rise to both of them. This means that the early embryo is not identified with one and only one human being. It is only after the appearance of the PS, when twinning is no longer possible, that we have the one-to-one correlation between the embryo and the future human person that would allow us to posit the embryo as the first stage in its development. On an identity criterion, it is permissible to discard or experiment on embryos prior to the formation of the PS, but not afterward. Note that the appearance of the PS has moral significance on grounds of both sentience and identity.

A new development in stem cell research is the creation of "synthetic embryos." Unlike IVF embryos, these synthetic embryos are not the product of fertilization.  They are assemblies of stem cells that can organize themselves into embryo-like structures. In a recent report, researchers at Harvard Medical School refer to them as "Synthetic Human Entities with Embryo-like Features," or SHEEFs.[1] Currently, SHEEFs are very simple assemblies of cells, but "... in the future, they may develop into far more complex forms... such as a beating human heart connected to a rudimentary brain, all created from stem cells."[2]

Should SHEEFs be protected by the same kinds of restrictions as IVF, or non-synthetic, embryos? Aach and his colleagues note the sentience rationale for the 14-day rule, and argue that SHEEFs might raise the same moral concerns as non-synthetic embryos. They might have the capacity to experience pain, even if they never develop a PS, but through some other mechanism for neural activity. This would make inapplicable to SHEEFs. They recommend giving up the 14-day rule, , and appealing directly to features that are associated with moral status. (Sentience is one, but there could be others, such as a beating heart.). To determine which features are associated with moral status will require both bioethical and biological research. Bioethicists will have to determine which features are morally relevant, while biologists will have to determine what biological structures are required for the relevant features to be functional.

The appeal of their proposal is that it seems to make more sense to consider directly which features have moral relevance, rather than focus on their biological markers. Nevertheless, I see some problems with their approach. First, is there any reason to think that embryos, synthetic or otherwise, might be capable of feeling pain? The existence of neural activity is not evidence of sentience.  Brain waves appear in the gestating fetus at about 8 weeks gestation age, but while brain waves are a necessary condition of sentience, they are not a sufficient condition. Precisely what degree of neural development is necessary, and when sentience is possible, is a matter of debate. The American College of Obstetricians and Gynecologists (ACOG) says that fetuses cannot feel pain before 24 weeks, because "the connections necessary to transmit signals from peripheral sensory nerves to the brain, as well as the brain structures necessary to process those signals, do not develop until at least 24 weeks of gestation."[3]Others think that pain perception in the fetus might be possible as early as 17 weeks. However, the claim that embryos in a petri dish could feel pain seems farfetched.

I do not dispute the value of research into moral standing. However, I think it is unlikely to result in a greater consensus than was reached by the various commissions decades ago. Unless and until there is a pressing reason to extend embryo research beyond 14 days, the 14-day rule seems a reasonable and workable limit.

[1]Aach et al, "Addressing the ethical issues raised by synthetic human entities with embryo-like features," eLife 2017. Accessed 3/27/17.

[2] Carl Zimmer, "Stem-Cell Engineering Raises Ethical Questions," New York Times, March 22, 2017, A20.

[3] ACOG, "Facts Are Important: Fetal Pain," Accessed March 29, 2017.


Tags:Bonnie Steinbockembryo researchIVFsynthetic embryosSynthetic Human Entities with Embryo-like FeaturesSHEEFssentiencebioethicists

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