The lure of human-animal chimera research

Andrew Fenton and Letitia Meynell call for moral reflection on the primacy of capacities for determining the moral status of non-human animals used in human-animal chimera research.


Last week Nature and Cell published research that takes us closer to creating non-human animal hosts for growing human organs. According to their Nature article, Tomoyuki Yamaguchi and colleagues modified rats to grow mouse pancreata that were then used to successfully treat diabetic mice. According to their Cell article, Jun Wu and colleagues modified embryonic pigs and allowed them to develop long enough to confirm that human cells could be successfully integrated into their tissues and organs.

Both studies represent advances in what is known as chimera research. Chimeras are animals (human or otherwise) possessing cells containing a genetic identity distinct from their parents and sometimes from their own species. Human-animal chimera research is largely motivated by shortages in human organs available for transplant. The hope is that in the not too distant future, part-human chimeric animals will grow what are effectively human organs to make up for the shortfall.

Cardiac muscle cells. Photo Credit: David C. Zebrowski, Felix B. Engel

Cardiac muscle cells. Photo Credit: David C. Zebrowski, Felix B. Engel

This research is receiving a good deal of media attention. Some scientists express cautious excitement about the breakthroughs while other scientists and ethicists express worries about the use of non-human animals in such invasive research and question its legitimacy.

Ethical confusion is understandable. The non-human animals typically used in this research – mice, rats, pigs and cows – don’t have a high moral status in our society. Some of their laboratory and non-laboratory kin are treated far worse than those used in chimera research: think of mice used in product testing or pigs raised on industrial farms. What’s more, the reasons for using mice in product testing or raising pigs on farms are more trivial than research aiming to create non-human animal organ donors.

Even among various professional organizations and other stakeholders trained in the scientific use of non-human animals, there is confusion in their favored ethical analyses of this research. Both funding agencies like the US National Institutes of Health (NIH) and researchers working in experimental animal science want to avoid making chimeric beings that possess enough human characteristics to be accorded the high moral status and protections currently reserved for humans. It’s often thought that the way to avoid this is to prohibit interventions in their brain development that will create ‘sophisticated’ cognitive capacities (like reflective self-awareness).

There is much more at stake in these kinds of disputes than the moral legitimacy of a branch of animal research. Indeed, these disputes strike at the very heart of moral reasoning and moral objectivity. An ethics that holds the interests of all non-human beings to be of lesser importance than the relevantly similar interests of humans can’t claim to be fair and objective. Apart from naked bias or partiality, why should humans enjoy ‘center stage’?

A growing number of philosophers and ethicists suggest that the mistake made by bodies like the NIH lies in our moral metric. Human genetic identity is not a good measure of moral status. To make the point, consider dolphins and whales. Whether you’re captivated by them or don’t often think about them, you’ve probably noticed the furor that surrounds hunting them, the outrage at their abuse, and calls to release captive dolphins and orcas to sanctuary. You may not know that some scientists have declared them persons and that a growing number of philosophers agree. As persons have, among other things, rights to life, bodily integrity, and some basic freedoms of movement, such scientists and philosophers believe that holding dolphins and whales against their will for reasons other than their best interests is wrong.

Whether you think these marine mammals are persons or not, it’s important to notice that they aren’t genetically close to humans. What’s of moral importance to those who seek their better treatment is their cognitive and affective capacities. These animals can suffer trauma, form deep bonds with members of their species, possess cultural traits that distinguish one group or community from others, and come to the aid of those around them. Such capacities can be used as reasons for respecting them and can guide us in how to treat them just as the capacities of our fellow humans inform what it means to treat each other with respect.

The concerns about creating chimeras that are too human for scientific exploitation should be replaced by a moral metric that reflects the primacy of capacities when determining moral status. Only when that is done will we have enough clarity of moral vision to judge the moral permissibility of human-animal chimera research.


Andrew Fenton is an Assistant Professor in the Department of Philosophy at Dalhousie University.

Letitia Meynell is an Associate Professor in the Department of Philosophy at Dalhousie University.

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