Opening Pandora's Box: Human-Nonhuman Chimeras

Part-Human Chimera Research

image showing cell division under microscope

The creation of part-human chimeric embryos and live-born chimeras could prove enormously beneficial as a tool for studying development and disease, testing therapeutic drugs, and generating tissues and organs for transplant.*

Chimeras are usually formed by merging human and animal embryos whilst hybrids have human and animal chromosomes. The most common objection to these techniques involves claims about interfering with nature – by creating ‘half-human, half-animals’. A further objection points to the lack of dignity associated with the creation of these embryos. Such an objection relies on a particular conception of the moral status of the embryo.**

On Thursday 15 April 2021, Professor Juan Carlos Izpisua Belmonte and his team announced in the journal Cell that they have injected human stem cells into monkey blastocytes, and succeeded in keeping some of the chimeric embryos alive for up to 20 days. It is hoped that by studying the 'crosstalk' between the monkey and human cells, it will soon be possible to generate human organs in different species that could help alleviate the worldwide shortage of organs for transplantation.

Full paper: Tao Tan, Jun Wu, Chenyang Si, et al, (2021), 'Chimeric contribution of human extended pluripotent stem cells to monkey embryos ex vivo', Cell, VOLUME 184, ISSUE 8, P2020-2032.E14, APRIL 15, 2021

*For an overview of the key ethical issues raised by part-human chimera research, and of possible regulatory approaches which may address these issues, see Julian Koplin and Julian Savulescu's article 'Time to rethink the law on part-human chimeras'.

**OUC's Katrien Devolder, Lauren Yip and Tom Douglas discuss the moral status of chimera, and the ethical issues surrounding such research in their freely available 2020 paper 'The Ethics of Creating and Using Human-Animal Chimeras', The ILAR Journal, Volume 60, Issue 3, Pages 434–438 [download author pre-print PDF]

Press Release

Response to the ISSCR Guidelines for Stem Cell Research and Clinical Translation

Published May 26, 2021 | By César Palacios-González

“The new ISSCR guidelines provide a much welcomed framework for research that many find ethically contentious.

Genome editing, the creation of human gametes in a lab, and the creation of human/non-human chimeras raise fundamental ethical issues that scientists can no longer overlook. The ISSCR guidelines put this research front and centre, making it now impossible for scientists to ignore the important ethical issues that they face. The guidelines also show why ethics must be an integral part of the education of scientists working in these areas.

However, there is a problem with how the guidelines justify that human heritable genome editing should not be permitted at this moment in time. Their main point is that reproductive human heritable genome editing ‘raise[s] unresolved ethical issues’. This is problematic because one could use this same justification for stopping all stem cell research.”

Dr César Palacios-González, Senior Research Fellow in Practical Ethics, Oxford Uehiro Centre for Practical Ethics, University of Oxford

Further Research

Read more about the ethics of chimera, in vitro gametogenesis, and stem cell research:

Chimeras intended for human gamete production: an ethical alternative? Reproductive Biomedicine Online (2017), 35(4), 387-390. [Palacios-González, César.]

Reproductive genome editing interventions are therapeutic, sometimes. Bioethics (2021). [Palacios‐González, César. ]

The regulation of mitochondrial replacement techniques around the world. Annual Review of Genomics and Human Genetics, 21 (2020): 565-586. [Cohen, I. Glenn, Eli Y. Adashi, Sara Gerke, César Palacios-González, and Vardit Ravitsky]

Human dignity and the creation of human–nonhuman chimeras. Medicine, Health Care and Philosophy, 18, no. 4 (2015): 487-499. [Palacios-González, César]

Multiplex parenting: in vitro gametogenesis and the generations to come. Journal of Medical Ethics, 40, no. 11 (2014): 752-758. [Palacios-González, César, John Harris, and Giuseppe Testa]


Forthcoming book, August 2021


Rethinking Moral Status, edited by Steve Clarke, Hazem Zohny, and Julian Savulescu

  • The first volume of its kind to consider how scientific and technological advancements impact our thinking about moral status
  • Explores how both current and future developments — from human brain organoids and artificial intelligence, to cyborgs and post-humans — may challenge ideas about moral status
  • Presents original ideas and discussion from leading philosophers and bioethicists

Common-sense morality implicitly assumes that reasonably clear distinctions can be drawn between the "full" moral status that is usually attributed to ordinary adult humans, the partial moral status attributed to non-human animals, and the absence of moral status, which is usually ascribed to machines and other artifacts. These implicit assumptions have long been challenged, and are now coming under further scrutiny as there are beings we have recently become able to create, as well as beings that we may soon be able to create, which blur the distinctions between human, non-human animal, and non-biological beings. These beings include non-human chimeras, cyborgs, human brain organoids, post-humans, and human minds that have been uploaded into computers and onto the internet and artificial intelligence. It is far from clear what moral status we should attribute to any of these beings.

There are a number of ways we could respond to the new challenges these technological developments raise: we might revise our ordinary assumptions about what is needed for a being to possess full moral status, or reject the assumption that there is a sharp distinction between full and partial moral status. This volume explores such responses, and provides a forum for philosophical reflection about ordinary presuppositions and intuitions about moral status.

This item is not yet published, but may be pre-ordered now for delivery when available (estimated 5 August 2021). Visit OUP website for further details.  ISBN: 9780192894076

Journal Articles

Devolder K, Yip, L, Douglas T. (2020), The Ethics of Human-Animal Chimeras and Animal-Animal Chimeras. The ILAR Journal, Volume 60, Issue 3, Pages 434–438 [download author pre-print PDF]

Julian Koplin and Julian Savulescu, (2019), 'Time to rethink the law on part-human chimeras', Journal of Law and the Biosciences, 6(1):37-50 [PMC6813936]

Dominic Wilkinson and Julian Koplin, (2019), 'Moral Uncertainty and the Farming of Human-Pig Chimeras', Journal of Medical Ethics, Vol: 45: 440-446 [PMC6691869]

Palacios-González, C, (2017), Chimeras intended for human gamete production: an ethical alternative? Reproductive Biomedicine Online (2017), 35(4), 387-390

Palacios-González, C, (2015), Human dignity and the creation of human–nonhuman chimeras. Medicine, Health Care and Philosophy, 18, no. 4 (2015): 487-499



Lithuanian National Radio: Radio programme discussing human-monkey embryos, Katrien Devolder (23 April 2021) [Segment begins at 19:50 with an introduction, Dr Devolder's contribution starts at around 21:50]

The ConversationFirst human-monkey embryos created – a small step towards a huge ethical problem, Julian Savulescu and César Palacios-González (22 April 2021)

BBC NewsHuman cells grown in monkey embryos spark ethical debate, Professor Julian Savulescu (by Helen Briggs, 16 April 2021)

Quoted in:

The CampusChimeric embryo may have medical implications (by Gabriella Brady, 23 April 2021)
BionewsResearchers generate human-monkey chimeric embryos (by Dr George Janes, 19 April 2021)
DT Next: Morality vs Science: Ethics of bridging the human-primate link (by Carla Bleiker, 19 April 2021)
Crux NowHuman-monkey embryo ‘deeply unethical,’ says Catholic bioethicist (by Charles Collins, 17 April 2021)
Conservative WomanToday’s talking point (by Kathy Gyngell, 17 April 2021)
Republic WorldExperts Raise Ethical Concerns Over Growing Human Cells In Monkey Embryos, by Riya Baibhawi (17 April 2021)
Silicon RepublicLab-grown human-monkey embryos raise ethical questions (by Jenny Darmody, 17 April 2021)
Sky NewsHuman cells grown in monkey embryos triggers 'Pandora's box' ethical concerns (16 April 2021)
Y108First-ever human-monkey hybrid created in 'chimera' embryo experiment (by Josh K. Elliott, 16 April 2021)
The SunMONKEY ME, MONKEY YOU First part-human, part-monkey embryo created by scientists sparks outcry (by Charlotte Edwards, 16 April 2021)
South China Morning Post: China-US scientists grow first human-monkey embryo, but is it ethical? (by Stephen Chen, 16 April 2021)
The GuardianHuman cells grown in monkey embryos reignite ethics debate (by Nicola Davis, 15 April 2021)

ScienceLab-grown embryos mix human and monkey cells, Dr Katrien Devolder (by Mitch Leslie, 16 April 2021) Vol. 372, Issue 6539, pp. 223

Quoted in BioEdgeHuman-monkey chimaeras grown for up to 20 days, (by Michael Cook, 17 April 2021)

The IndependentWhat are the ethical implications of growing human cells in monkey embryos?: Ethicists tell The Independent of urgent need for wider debate ahead of more developed experiments, Professor Dominic Wilkinson (by Andy Gregory, 17 April 2021)

BBC Three Counties Radio: Interview on human-monkey chimera experiments, Katrien Devolder (16 April 2021) [no link]

talkRADIO: Interview on human-monkey chimera experiments, Katrien Devolder (16 April 2021)

BBC World News TV: Interview on human-monkey chimera experiments, Katrien Devolder (16 April 2021)

Times RadioInterview on human-monkey chimera experiments, Katrien Devolder (16 April 2021) [no link]

Blogs and Podcasts

The ConversationFirst human-monkey embryos created – a small step towards a huge ethical problem, Julian Savulescu and César Palacios-González (22 April 2021)

Practical Ethics in the NewsCross-Post: The Moral Status of Human-Monkey Chimeras. Published April 20, 2021 | By Julian Savulescu and Julian Koplin [first published on Pursuit]

Practical Ethics in the News: Japan to Allow Human-Animal Hybrids to be Brought to Term. Published August 6, 2019 | By Mackenzie Graham

Rethinking Moral Status Workshop: 'Chimeras, Superchimps and Post-persons; Species Boundaries and Moral Status Enhancements', Sarah Chan (June 2019)

Other recorded sessions of our two-day workshop 'Rethinking Moral Status' are available on our podcast album here.