Growing Human Cells in Monkey Embryos Is Problematic—But Not for the Reasons People Think

Last week scientists revealed a breakthrough: for the first time, humans have created human-monkey chimera embryos, that is, embryos with both human and monkey cells. This is noteworthy because combining human and nonhuman cells is no easy task. Typically one kind of cell dominates the other, but in this case, they got along relatively well. This suggests that we might be able to combine human and nonhuman cells even more in the future.

Not surprisingly, reactions to this news have been mixed. Many people are excited about the possibilities. If we create human-nonhuman chimeras, then we can use them for medical research and organ transplantation. But many other people are worried. If we create human-nonhuman chimeras, are we playing God? Are we blurring traditional species distinctions? How should we treat these chimeras? What happens if they become more human-like? 

These reactions all miss the main problem with chimera use. They all focus on what makes chimera use different from conventional animal use, and they all assess the pros and cons with these differences in mind. But the main problem with chimera use lies in the similarities with conventional animal use, not the differences: Humans are once again planning to create sentient beings so that we can exploit and exterminate them for our own benefit. 

Take the idea of using chimeras for medical research and organ transplantation. In the case of medical research, the aim is to create chimeras who are “human” enough that the research can benefit us, but “nonhuman” enough that the harms can be acceptable to us. And in the case of organ transplantation, the aim is to create chimeras with human organs so that we can take the organs for ourselves even if the chimeras still need them too.

These intended applications of chimera research are morally unacceptable. But what makes them unacceptable has nothing to do with the fact that chimeras are partly human and partly nonhuman. Instead, what makes them unacceptable is the fact that they involve creating animals with consciousness, emotionality, a sense of self, and social awareness, all so that we can then harm and kill them for our own benefit without the possibility of their consent.  

Of course, it might be that some kinds of chimera use can be morally acceptable. For example, in vitro research on chimeric embryos is less clearly harmful than in vivo research on chimeric animals, even though both kinds of research raise ethical questions. But such exceptions aside, we should be deeply troubled by scientific developments that promise more, rather than less, violence against vulnerable populations for our own benefit. 

In contrast, the novel issues involved with chimera use are less concerning. For example, if we create chimeras, are we playing God and blurring traditional species distinctions? Yes, in a way. But there is nothing wrong in principle with improving our ability to explain, predict, and control reality, including by creating new animals. What matters is that we exercise this power responsibly by treating everyone involved with respect and compassion. 

Similarly, if we create chimeras, how should we treat them? Should we apply “human” ethical standards to our treatment of these individuals, in which case we should treat them well? Or should we apply “nonhuman” ethical standards to our treatment of these individuals, in which case we can treat them badly? Also, what happens if chimeras become more human-like? Should we treat them more respectfully or compassionately in that case?

But while these questions might be concerning, note that they arise only because of our assumption that we can treat some individuals better than others on the basis of species membership alone. If we instead assumed that we should treat all individuals well independently of species membership, then these questions would all but disappear. Thus, the problem is once again with the old—in this case, our speciesist double standards—not with the new.

Of course, this is not to say that we should ignore the new problems involved with chimera use. Insofar as chimeras might have unpredictable interests and needs, we face more uncertainty about how to treat them well. And insofar as current institutions do accept speciesist double standards, it matters a great deal whether we apply “human” or “nonhuman” ethical standards to our treatment of chimeras within these institutional contexts.  

But the new problems involved with chimera use pale in comparison with the old ones. At present, we are killing more than 100 million lab animals each year, along with billions of farmed animals and trillions of wild animals. This development simply promises more of the same. While it might be old news, our tendency to violently oppress vulnerable others—human and nonhuman alike—is the real news, and we need to make sure to keep it in focus.

An earlier version of this argument was presented at a meeting supported by The U.S. National Human Genome Research Institute under award number 1 R01 HG010168 (Johnston, Maschke Hyun, PIs), “Actionable Ethics Oversight for Human-Animal Chimera Research.”