How should we treat beings of uncertain moral status?

By Julian Koplin and Dominic Wilkinson

Advances in stem cell science are making it possible to create new kinds of living beings. Using a technique known as interspecies blastocyst complementation, it may soon be possible to grow human organs inside of human-animal chimeras. Most of the tissues of these chimeric animals would be composed of a mix of (primarily) animal and (some) human cells. However, the specifically targeted organs would be wholly human.

Interspecies blastocyst complementation has many exciting applications. Chimeric animals with human organs could prove useful for biomedical research, and they could potentially even be used to generate human organs for transplant. However, interspecies blastocyst complementation also raises some difficult ethical questions, particularly in cases where human cells might contribute to chimeric animals’ brains. Could chimeric animals with humanised brains develop new cognitive abilities – and, if so, could these cognitive abilities affect their moral status? Should researchers develop techniques to ensure human cells don’t contribute to chimeric animals’ brains? Conversely, would it ever be permissible for researchers to create chimeric animals with wholly human brains – for example, in order to study human neurodegenerative disorders?

This is not the only context where these kinds of questions arise. Since we wrote our paper, researchers from China’s Kumming Institute of Zoology announced that they had genetically modified macaque monkeys using genes associated with human intelligence. These transgenic monkeys displayed better short-term memory than their wild-type counterparts, and in some respects their brain development resembled that of a human’s. Like the part-human chimera research discussed in our paper, this transgenic monkey research raises difficult questions about the moral status of animals with humanised brains.

Our paper approaches this controversy from a slightly unusual angle. We do not argue directly for or against any of these practices. Instead, we highlight a tension between two common moral views: that creating chimeric pigs with humanised brains is morally problematic, and that farming pigs for food is morally benign. We show how the same style of argument can be used to object to both practices, and we argue that we should either accept this argument in relation to both human-pig chimeras and regular pigs, or we should reject it in relation to both.

First, we identify one key factor that worries people about interspecies blastocyst complementation: that it is incredibly hard to pinpoint the point at which the ‘humanization’ of a chimeric animal’s brain could cause it to develop full moral status. The challenges here are twofold. It is difficult to know how to test whether a chimeric animal has developed the necessary cognitive abilities, and it is difficult to work out precisely what cognitive abilities are relevant to chimeric animals’ moral status. This matters, morally, because if a chimeric animal develops full moral status and (failing to recognise this fact) we harm it anyway, we would commit a serious wrong.

Next, we show how the same style of argument could be levelled against a practice that is much less controversial than interspecies blastocyst complementation: the practice of farming and killing nonhuman animals in order to eat them. Think about how difficult it would be to assess the moral status of a regular pig. The challenges here are twofold. Our understanding of pig cognition is extremely patchy, largely because it is difficult to know how best to test the cognitive abilities of nonhuman animals. (The available research does suggest that pigs are cleverer than many people give them credit for.) At the same time, it is difficult to work out precisely what cognitive abilities pigs would need to display for us to grant them full moral status. This matters, morally, because if a pig possesses full moral status and (failing to recognise this fact) we harm it anyway, we would commit a serious wrong.

Although our paper does not discuss the insertion of human intelligence genes into monkeys, a similar pair of arguments seems to apply. People seem to be concerned by the possibility that monkeys with humanised brains could develop full moral status. The challenges here resemble those discussed above; it is philosophically difficult to know what set of capacities confer full moral status, and it is practically difficult to work out how to identify these capacities in nonhuman primates. However, these same challenges make it difficult to assess the moral status of regular macaque monkeys (which display strikingly complex behaviours even when their brains are unmodified). If we should not create monkeys with humanised brains because their moral status is uncertain, then perhaps we also shouldn’t experiment on regular monkeys. After all, their moral status is uncertain too.

It might seem strange for our discussion of monkeys with humanised brain genes to segue into a general discussion of monkey experimentation. It might seem stranger still for our paper on part-human chimera ethics to take a detour into the ethics of eating meat. But we think this is exactly what is required. The ethics of part-human chimera research are bound up with – and cannot be considered in isolation from – these broader questions of animal ethics. To consider the moral limits of part-human chimera research, we also need to reconsider the ways that humans currently utilise nonhuman animals. If we want to understand how we ought to treat part-human chimeric animals, we will need to work out how we ought to treat any beings of uncertain moral status.


Paper title: Moral Uncertainty and the Farming of Human-Pig Chimeras [OPEN ACCESS]

Author(s): Julian Koplin1,2 and Dominic Wilkinson1,3,4


  1. Murdoch Children’s Research Institute, Melbourne, Australia
  2. University of Melbourne Law School, Melbourne, Australia
  3. Oxford Uehiro Centre for Practical Ethics, Faculty of Philosophy, University of Oxford, UK
  4. John Radcliffe Hospital, Oxford, UK

Competing interests: n/a

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