Article
Human-Animal Chimeras: The Moral Insignificance of Uniquely Human Capacities
Julian J. Koplin,
Julian J. Koplin
Search for more papers by this authorJulian J. Koplin,
Julian J. Koplin
Search for more papers by this authorAbstract
Human-animal chimeras—creatures composed of a mix of animal and human cells—have come to play an important role in biomedical research, and they raise ethical questions. This article focuses on one particularly difficult set of questions—those related to the moral status of human-animal chimeras with brains that are partly or wholly composed of human cells. Given the uncertain effects of human-animal chimera research on chimeric animals’ cognition, it would be prudent to ensure we do not overlook or underestimate their moral status. However, to assess moral status, we first need to determine what kinds of capacities are morally relevant. The standard view holds that it matters, morally, if chimeric animals develop uniquely human cognitive capacities. I argue that this view is mistaken, highlighting three problems with it: that we can think of examples of uniquely human cognitive capacities that are not morally significant, that we can think of examples of morally significant cognitive capacities that are not uniquely human, and that evidence that some cognitive capacity is shared with nonhuman animals does not undermine claims that this capacity is morally significant. We need a better framework for thinking about the moral status of part-human beings.
Notes
- 1Chimeras are therefore distinct from other forms of “interspecies creatures” such as hybrids (which are formed from zygotes from different species) and genetically altered animals (which are created by inserting genes from one species into animals from another). Hybrids and genetically altered animals have a mixture of human and animal DNA, whereas part-human chimeras are composed of a mixture of human and animal cells ( Academy of Medical Sciences, Animals Containing Human Material [London: Academy of Medical Sciences, 2011]).
- 2R. R. Behringer, “Human-Animal Chimeras in Biomedical Research,” Cell Stem Cell 1, no. 3 (2007): 259–62.
- 3J. Wu et al., “Stem Cells and Interspecies Chimaeras,” Nature 540 (2016): 51–59.
- 4H. T. Greely et al., “Thinking about the Human Neuron Mouse,” American Journal of Bioethics 7, no. 5 (2007): 27–40.
- 5B. Capps, “Do Chimeras Have Minds? The Ethics of Clinical Research on a Human-Animal Brain Model,” Cambridge Quarterly of Healthcare Ethics 26 (2017): 577–91.
- 6Weissman’s experiments were never actually conducted. However, other techniques are currently in use to generate human neurons inside the brains of human-mouse chimeras. For a recent example, see I. Espuny-Camacho et al., “Hallmarks of Alzheimer’s Disease in Stem-Cell-Derived Human Neurons Transplanted into Mouse Brain,” Neuron 93 (2017): 1066–81.
- 7F. Baylis and A. Fenton, “Chimera Research and Stem Cell Therapies for Human Neurodegenerative Disorders,” Cambridge Quarterly of Healthcare Ethics 16 (2007): 195–208; S. Levine and L. Grabel, “The Contribution of Human/Non-human Animal Chimeras to Stem Cell Research,” Stem Cell Research (2017): 128-34; A. De Los Angeles et al., “Human-Monkey Chimeras for Modeling Human Disease: Opportunities and Challenges,” Stem Cells and Development 27 (2018): 1599-604.
- 8See, for example, M. Greene et al., “Moral Issues of Human–Non-human Primate Neural Grafting,” Science 309 (2005): 385–86; P. Karpowicz, C. B. Cohen, and D. Van der Kooy, “Developing Human-Nonhuman Chimeras in Human Stem Cell Research: Ethical Issues and Boundaries,” Kennedy Institute of Ethics Journal 15, no. 2 (2005): 107-34.
- 9T. Rashid, T. Kobayashi, and H. Nakauchi, “Revisiting the Flight of Icarus: Making Human Organs from PSCs with Large Animal Chimeras,” Cell Stem Cell 15, no. 4 (2014): 406–9.
- 10J. Wu et al., “Interspecies Chimerism with Mammalian Pluripotent Stem Cells,” Cell 168 (2017): 473–86, at 484.
- 11A. Kurtz and S. J. Oh, “Non-human Primate Chimeras Make a Move,” Stem Cell Investigation 3, no. 13 (2016): doi: 10.21037/sci.2016.04.03.
- 12A. Hagan-Brown, M. Favaretto, and P. Borry, “Newspaper Coverage of Human-Pig Chimera Research: A Qualitative Study on Select Media Coverage of Scientific Breakthrough,” Xenotransplantation 24, no. 4 (2017): e12317.
- 13See, for example, R. Bourret et al., “Human-Animal Chimeras: Ethical Issues about Farming Chimeric Animals Bearing Human Organs,” Stem Cell Research & Therapy 7, no. 1 (2016): 1–7; Wu et al., “Stem Cells and Interspecies Chimaeras.”
- 14L. Gruen, “The Moral Status of Animals,” in Stanford Encyclopedia of Philosophy, ed. E. N. Zalta, Stanford University, 2017, article first published 2011, substantively revised 2017, https://plato.stanford.edu/archives/fall2017/entries/moral-animal/; M. Piotrowska, “Transferring Morality to Human-Nonhuman Chimeras,” American Journal of Bioethics 14, no. 2 (2014): 4–12.
- 15X. Han et al., “Forebrain Engraftment by Human Glial Progenitor Cells Enhances Synaptic Plasticity and Learning in Adult Mice,” Cell Stem Cell 12, no. 3 (2013): 342–53; M. S. Windrem et al., “A Competitive Advantage by Neonatally Engrafted Human Glial Progenitors Yields Mice Whose Brains Are Chimeric for Human Glia,” Journal of Neuroscience 34 (2014): 16153-61.
- 16For two notable exceptions, see D. DeGrazia, “Human-Animal Chimeras: Human Dignity, Status, and Species Prejudice,” Metaphilosophy 38, no. 2-3 (2007): 309–29, and S. Porsdam Mann, R. Sun, and G. Hermeren, “A Framework for the Ethical Assessment of Chimeric Animal Research Involving Human Neural Tissue,” BMC Medical Ethics 20, no. 10 (2019): doi:10.1186/s12910-019-0345-2.
- 17Academy of Medical Sciences, Animals Containing Human Material; for another example of this view, see L. Y. Cabrera Trujillo and S. Engel-Glatter, “Human-Animal Chimera: A Neuro Driven Discussion? Comparison of Three Leading European Research Countries,” Science and Engineering Ethics 21, no. 3 (2015): 595–617.
- 18Ibid., 6 and 47. For similar arguments concerning humanlike consciousness, see Greely et al., “ Thinking about the Human Neuron Mouse,” 35; Bourret et al., “Human-Animal Chimeras”; and Capps, “Do Chimeras Have Minds?”
- 19 Greely et al., “ Thinking about the Human Neuron Mouse,” 35.
- 20I. Hyun, “What’s Wrong with Human/Nonhuman Chimera Research?,” PLoS Biology 14, no. 8 (2016): e1002535; see also Karpowicz, Cohen, and Van der Kooy, “Developing Human-Nonhuman Chimeras,” 334.
- 21 Levine and Grabel, “ Contribution of Human/Non-human Animal Chimeras,” 130.
- 22H. T. Greely, “Academic Chimeras?,” American Journal of Bioethics 14, no. 2 (2014): 13–14. An advisory report from the Ethics and Public Policy Committee of the International Society for Stem Cell Research takes a subtly different approach. The report holds that all part-human chimera research—including research with animals with humanlike minds—should be treated according to existing principles of animal welfare, while research with the “known, intended, or well-grounded significant potential to create humanized [emphasis added] cognition, awareness, or other mental attributes” should be subjected to especially close scrutiny. Implicitly, then, the report treats distinctly human capacities as if they have special moral significance (I. Hyun et al., “Ethical Standards for Human-to-Animal Chimera Experiments in Stem Cell Research,” Cell Stem Cell 1, no. 2 [2007]: 159-63).
- 23 Academy of Medical Sciences, Animals Containing Human Material, 47–48.
- 24 German Ethics Council, Human-Animal Mixtures in Research (Berlin: German Ethics Council, 2011), at 77-78.
- 25 Ibid., 78.
- 26 Ibid., 80–83.
- 27 Ibid., 84–85.
- 28I. Hyun, Bioethics and the Future of Stem Cell Research (New York: Cambridge University Press, 2013), 144. For further elaborations of this view, see Hyun, “What’s Wrong with Human/Nonhuman Chimera Research?”; I. Hyun, “Illusory Fears Must Not Stifle Chimaera Research,” Nature 537 (September 13, 2016): doi:10.1038/537281a; and I. Hyun, “The Ethics of Chimera Creation in Stem Cell Research,” Current Stem Cell Reports 4, no. 3 (2018): 235-39.
10.1038/537281a Google Scholar
- 29 Academy of Medical Sciences, Animals Containing Human Material, 48.
- 30 German Ethics Council, Human-Animal Mixtures, 77–78.
- 31 Hyun, Bioethics and the Future, 144.
- 32G. G. Gallup, “Self-awareness in Primates,” American Scientist 67, no. 4 (1979): 417–21.
- 33D. DeGrazia, “Self-awareness in Animals,” in The Philosophy of Animal Minds, ed. R. Lurz (Cambridge: Cambridge University Press, 2009): 201–17; M. Rowlands, “Are Animals Persons?,” Animal Sentience: An Interdisciplinary Journal on Animal Feeling 1, no. 10 (2016): 1-18.
10.1017/CBO9780511819001.012 Google Scholar
- 34E. Dere et al., “The Case for Episodic Memory in Animals,” Neuroscience & Biobehavioral Reviews 30, no. 8 (2006): 1206–24.
- 35M. Tennesen, “More Animals Seem to Have Some Ability to Count,” Scientific American, September 1, 2009.
- 36F. De Waal, Are We Smart Enough to Know How Smart Animals Are? (New York: W.W. Norton, 2016).
- 37M. Bekoff and J. Pierce, Wild Justice: The Moral Lives of Animals (Chicago: University of Chicago Press, 2009).
10.7208/chicago/9780226041667.001.0001 Google Scholar
- 38For a review of the relevant literature, see A. Jaworska and J. Tannenbaum, “The Grounds of Moral Status,” in Stanford Encyclopedia of Philospohy, ed. E. N. Zalta, 2013, Stanford University, 2018, article first published 2013, substantively revised January 10, 2018 https://plato.stanford.edu/archives/spr2018/entries/grounds-moral-status/.
- 39K. Andrews et al., “ Brief by Amici Curiae Philosophers in Support of the Petitioner-Appellant, Nonhuman Rights Project, Inc. v. Lavery,” 2018, accessed September 23, 2019, at https://www.nonhumanrights.org/content/uploads/In-re-Nonhuman-Rights-v.-Lavery-Proposed-Brief-by-PHILOSOPHERS-74435.pdf.
- 40D. DeGrazia, “Great Apes, Dolphins, and the Concept of Personhood,” Southern Journal of Philosophy 35, no. 3 (1997): 301–20, at 302.
- 41P. Shapiro, “Moral Agency in Other Animals,” Theoretical Medicine and Bioethics 27, no. 4 (2006): 357–73; C. Nicol, “Do Elephants Have Souls?,” New Atlantis: A Journal of Technology & Society 38 (2013): 10-70.
- 42B. Keim, “An Elephant’s Personhood on Trial,” Atlantic, December 28, 2018.
- 43This account of moral status might also have problematic implications for the treatment of “nonparadigm humans”—humans who have not and will not develop these capacities (for example, due to cognitive impairment) but nonetheless seem to have greater moral standing than we currently extend to research animals (see A. Norcross, “Animal Experimentation, Marginal Cases, and the Significance of Suffering,” in The Ethics of Animal Research: Exploring the Controversy, ed. J. R. Garrett [Cambridge: MIT Press, 2012]).
- 44 As mentioned above, whether the specific capacities suggested to date are uniquely human is open to question.
- 45This view is commonly attributed to Descartes. While it is questionable whether Descartes held it, he certainly took the possibility seriously, and many of his followers explicitly claimed that nonhuman animals lacked consciousness (P. Harrison, “Descartes on Animals,” Philosophical Quarterly 42, no. 167 [1992]: 219–27).
- 46P. Low et al., “ The Cambridge Declaration on Consciousness,” paper presented at the Francis Crick Memorial Conference, Cambridge, England, July 7, 2012, http://fcmconference.org/img/CambridgeDeclarationOnConsciousness.pdf.
- 47A. Seed and R. Byrne, “Animal Tool-Use,” Current Biology 20, no. 23 (2010): R1032–R1039; De Waal, Are We Smart Enough to Know How Smart Animals Are?
- 48Frans De Waal has listed several other examples, both in Are We Smart Enough to Know How Smart Animals Are? (pp. 21-22) and elsewhere. For instance, elephants were once thought to lack mirror self-recognition. However, it turned out that this was simply because the mirrors used in these initial experiments were too small and too far away for the elephants to see themselves properly. The results were very different once elephants were tested using an appropriately sized mirror, which measured roughly 2.5 meters in height (J. M. Plotnik, F. B. De Waal, and D. Reiss, “Self-recognition in an Asian Elephant,” Proceedings of the National Academy of Sciences 103, no. 45 [2006]: 17053–57).
- 49Many opponents of chimpanzee personhood would presumably agree. Rather than tying full moral status to species membership per se, critics of chimpanzee personhood often emphasize the cognitive differences between humans and chimpanzees (see, for example, J. Taylor, Not a Chimp: The Hunt to Find the Genes That Make Us Human [Oxford: Oxford University Press, 2010]).
- 50T. Matsuzawa, “Evolution of the Brain and Social Behavior in Chimpanzees,” Current Opinion Neurobiology 23, no. 3 (2013): 443–49.
- 51 Nothing in the above argument rules out the possibility that humans are the only species to possess (full) moral status. However, if this is the case, it must be because humans alone possess some set of capacities that are morally significant in their own right. These capacities would not confer (full) moral status because humans happen to be the only species to possess them.
- 52D. DeGrazia, Taking Animals Seriously: Mental Life and Moral Status (Cambridge: Cambridge University Press, 1996).
10.1017/CBO9781139172967 Google Scholar
- 53This view is consistent with a broad range of approaches to animal ethics, including Peter Singer’s utilitarian argument for equal consideration of equal interests (which allows that not all interests are equal), Tom Regan’s rights-based argument that all animals have equal inherent value (which acknowledges that different kinds of beings require different kinds of rights), Jeff McMahan’s two-tier account of moral status (which grants self-conscious beings greater protections than others), and Shelly Kagan’s hierarchical approach to animal ethics (which sorts different beings into different “tiers” of moral status, each of which deserves different kinds of treatment) (P. Singer, Animal Liberation, 2nd ed. [New York: Random House, 1990]; T. Regan, The Case for Animal Rights [Berkeley, CA: University of California Press, 1983]; J. McMahan, The Ethics of Killing: Problems at the Margins of Life [New York: Oxford University Press, 2002]; S. Kagan, “For Hierarchy in Animal Ethics,” Journal of Practical Ethics 6, no. 1 [2018]: http://www.jpe.ox.ac.uk/papers/for-hierarchy-in-animal-ethics/).
- 54 DeGrazia, Taking Animals Seriously.
- 55J. Shepherd, Consciousness and Moral Status (New York: Routledge, 2018).
10.4324/9781315396347 Google Scholar
- 56 DeGrazia, Taking Animals Seriously; DeGrazia, “Self-awareness in Animals.”
- 57W. Whitman, “I Sing the Body Electric,” in Leaves of Grass (1855; repr., Illinois: Project Gutenberg, 2008), https://www.gutenberg.org/files/1322/1322-h/1322-h.htm.
- 58C. Foster, Being a Beast (London: Profile Books, 2016), 40.
- 59G. Saunders, Fox 8: A Story (New York: Random House, 2018).
- 60H. M. Johnson, “Unspeakable Conversations,” New York Times Magazine, February 13, 2003.
- 61 Shepherd, Consciousness and Moral Status, 98–99.
- 62 Foster, Being a Beast, 39.
- 63 Hyun, Bioethics and the Future, 139.
- 64 I have glossed over some complexities here. For example, it might be asked whether phenomenal value should be assessed using subjective criterion (which defines one’s good in terms of one’s own desires or values) or some kind of objective criterion (which defines one’s good against some external, “objective” standard). I thank an anonymous reviewer for raising this point.
