The predation problem is arguably the most difficult and controversial part of wild animal suffering. In what follows, I want to make an argument in favor of the idea to herbivorize predators (HP). I will not argue for its possibility or feasibility, because natural evolution already led to the herbivorization of some carnivorous species such as the giant panda, the red panda, the spectacled bear and the kinkajou. Here I present a moral argument, with the intention to open a discussion about whether animal welfare effective altruists should consider herbivorizing predators as a cause area. If the argument is sound, it entails that individuals are allowed to, and society has an obligation to apply safe, animal-friendly and effective means (technologies) to herbivorize predators, and at least we should start doing scientific research to look for such technologies.

The first step of the argument, based on an analogy between predation and organ transplantation, shows why predation is bad. The second step extends this analogy with a thought-experiment to argue why HP is the best solution. 

Consider two cases.

1.               Feeding predation: a lioness feeds her cub by predating on prey. More specifically: one animal (the lioness) kills a few other animals (sacrificed animals or victims), takes parts of their bodies (muscle tissue), puts these body parts in the body of a beneficiary animal (the cub), in order for that beneficiary animal to survive.

2.               Organ transplantation: a surgeon saves patients by transplanting organs. More specifically: a human (the surgeon) kills an innocent child (a sacrificed child or victim), takes parts of that child’s body (kidney, spleen, lungs,…), puts these body parts in the bodies of a few beneficiary children (patients who need organs), in order for those beneficiary children to survive.

The similarities between the two cases are clear: both cases involve killing innocent sentient beings and using their body parts for the same objective of saving other sentient beings. In both cases, someone’s autonomy, freedom, welfare, flourishing or any other value that refers to the state of an individual, is violated. Both the prey animals and the sacrificed child are harmed. But there are two dissimilarities worth discussing. 

First, the surgeon is a moral agent (able to make moral judgments and reflect morally), whereas the lioness is not. But this difference is irrelevant, if for example we assume that the moral value (badness) of a situation such as organ transplantation does not depend on a cognitive ability of individuals who are not strongly affected by the choice. The beneficiary and sacrificed children are strongly affected by the choice to transplant organs, but the surgeon is not. Hence, suppose the surgeon lost her cognitive ability to reflect morally, but was still able to perform surgeries. The surgeon could even be a robot who is not even affected by anything. That would not improve the moral value of the organ transplantation case. A surgeon would not suddenly get a right or privilege to sacrifice children for organ transplantations when that surgeon loses one of her cognitive abilities. Neither would the value of the predation case change when the lioness develops a cognitive ability to make moral judgments. Also note that in the two cases, neither the animals nor the children are assumed to be moral agents. This means that moral agency is irrelevant, refuting arguments in favor of predation that refer to the lack of moral agency of predators (e.g. Regan, 1983; Ebert & Machan, 2012).

Second, the children in the organ transplantation case belong to the human species, whereas the animals in the feeding predation case do not. This difference is irrelevant, if for example we assume anti-speciesism: the moral value of a situation does not depend on the species memberships of the involved individuals. It would be arbitrary to have a moral principle that entails that the moral value of a situation changes when a beneficiary individual belongs to another species, or when a sacrificed individual belongs to another species. The badness of a situation may be based on individual values, such as welfare or the right not to be used as merely a means. But these values do not refer to species membership.

As a consequence of the similarities between the feeding predation and organ transplantation cases, major moral theories entail that the moral value of feeding predation is at least as low as the moral value of organ transplantation. For deontological or rights-based theories, everything that is relevant for basic rights, such as the right not to be killed or the right not to be used as merely a means, is similar in both predation and transplantation cases: innocent individuals are killed and their bodies are used as a means against their will. If transplantation is bad because it violates a deontological principle, then the same goes for predation. For utilitarian or consequentialist theories, the case of predation is worse than transplantation, because in predation, many individuals are sacrificed for the life of one, whereas in transplantation one individual is sacrificed for the lives of many.

To complete the first step of the argument, that general predation is bad, we need a few more assumptions. First, of course, we need to assume that the described organ transplantation situation is bad. Second, assume that the moral value of general predation and feeding predation are the same: it doesn’t matter whether the lioness feeds herself or her cub. 

Third, and less trivially, assume scope-insensitivity: the moral value of a situation is independent from the scope of that situation, i.e. the number of individuals involved or the number of actions made. Suppose there are many surgeries performed by many surgeons to benefit many children who need organs. For clearness of presentation, denote the group of the surgeons and beneficiary children as the transplantators (just like lions and their cubs are called predators), and the sacrificed children as organ people (just like zebra are called prey animals). 

It could be the case that large-scale organ transplantation had some benefits, for example by controlling the population of organ people. Imagine that without organ transplantation, the children who belong to the group of organ people survive and procreate to such a degree that that group becomes overpopulated. That could result in mass starvation or overexploitation of scarce resources. By sacrificing children, the transplantators reduce the population size of the organ people to such a degree that overpopulation is avoided. This could be a benefit of large-scale organ transplantation, but we assume that this benefit cannot make organ transplantation good all things considered. This assumption is valid if for example there are better alternatives to avoid organ people overpopulation (such as using contraceptives).

With the above assumptions, we can derive that large-scale, general predation is not better than small-scale feeding predation, which is at least as bad as organ transplantation, which is bad. The next question is: what is the best solution? Arrest the surgeons and let the transplantators die? Painlessly kill the predators (Bramble, 2021)? To answer this question, we can turn the organ transplantation case into a hypothetical scenario as a thought-experiment.

Suppose the transplantator children have inherited from their parents genetic mutations that result in organ failure. This genetic defect is part of the biological (genetic) identity of those children and their parents. The parents of those children survived due to organ transplantations. As they belong to the group of transplantators with a unique genetic makeup, the acquired genes can be called transplantator genes. If the transplantator children survive by receiving organs, the progeny of those transplantator children will also inherit those transplantator genes and hence will also require organ transplantation to survive. 

A first option to consider, is stopping the surgeons from killing organ children. If no other options are available, organ people have a permissibility to stop the surgeons. This permissibility is based on a right to self-defense. Stopping surgeons violates the autonomy of those surgeons, but the surgeons themselves violate the autonomy of organ people by killing them. If stopping surgeons was impermissible, it would be permissible to stop organ people from stopping the surgeons. This would violate the autonomy of the organ people. Hence, someone’s autonomy is always violated and autonomy violations cannot be invoked to prohibit stopping the surgeons. Of course, stopping surgeons means letting the transplantator children die (or painlessly kill them, if that is the most humane option). Hence, this first option is not ideal, because it violates many rights (such as the rights to live, eat, play and procreate) and reduces the lifetime well-being of the transplantator children. 

The second option worth considering, is the use of technologies such as synthetic organs and contraceptives. Suppose synthetic (lab-grown) organs can be produced and used for organ transplantation to save the transplantator children. In the long run, using synthetic organs might become too unfeasible because these organs could be very expensive. One could produce synthetic organs to save the already born transplantator children, but if those children procreate, a constant new supply of expensive synthetic organs is required. To avoid this problem, suppose contraceptives for transplantator children are available. The second option comes down to saving the currently alive transplantator children using synthetic organs, and then sterilizing them such that the population of transplantators goes extinct.

This second option is at least as good (permissible) as the first option, because it better respects the rights to live of transplantator children. Hence, if synthetic organs and contraceptives are available, individuals have a permissibility to compel the surgeons to use the synthetic organs, and a permissibility to stop the procreation of transplantator children using the contraceptives. However, this second option is not ideal yet, because it still violates the right to procreate and harms transplantator people who have a desire to procreate. 

So suppose a third option is available: the use of gene-editing methods that change the genes that cause the organ failure, such that the transplantator children can procreate, but their offspring no longer have the genetic defect that makes their survival dependent on organs of other children. This is comparable to herbivorizing predators. As this option respects the rights to live and procreate, it is better than the first two options. The autonomy, freedom and welfare of the transplantators are maximally respected in such a way that the gene-edited transplantators can fully respect the autonomy, freedom and welfare of the organ people. Hence, individuals are permitted to alter the transplantator genes if this does not cause more harms or risks than the harms and risks caused by organ transplantation. 

Gene-editing is consistent with the preferences of the offspring of the gene-edited children. Imagine as a thought-experiment that we find out that our ancestors were once transplantators: they had to kill other humans for their organs, in order to survive. But many years ago, the organ people decided to genetically modify the transplantators such that they no longer had to kill humans. We are the descendants of those gene-edited ancestors. Would we now say that what those organ people did is immoral? Would we say that it would have been better if we were still transplantators with transplantator genes? Would we prefer a world where we and many other humans who are currently alive would not exist, and murderous transplantator humans would exist instead? Would we say that being transplantator is our true nature and that it is bad that we have lost this true nature due to the genetic modification? Would we say that the loss of our true transplantator nature is worse than the loss of billions of human lives who are killed by transplantators? No, we are glad not to be murderous transplantators. We do not object against our newly acquired non-transplantory true nature, as long as we can live happy and healthy lives. We have no objections against our ancestors being gene-edited in the right way.

The third option also maximally respects some non-individualistic values such as genetic diversity, conservation of populations, preservation of genealogical lineages or continuation of natural evolution. These values do not refer to the state of an individual and can be considered as ecocentric values. The transplantator genes are eradicated, but the gene-edited transplantaror descendants may still have genes different from the organ people. The option that allows for the survival of gene-edited transplantator descendants has more genetic diversity than the options to kill or sterilize transplantators. As those people can procreate, their populations and genealogical lineages are preserved, whereas allowing organ transplantation means the genealogical lineages of the sacrificed organ children are terminated. Natural evolution still continues when gene-edited transplantator descendants can procreate, whereas the evolution of a population of organ children stops when those organ children are killed for organ transplantation. 

Furthermore, once the transplantator children’s genes are edited, no further interventions are required. This could make the third option the most cost-effective and feasible in the long run. As individualistic values such as autonomy and welfare and non-individualistic values such as diversity and genealogy are maximally respected with gene-editing, and if gene-editing is sufficiently cost-effective and safe, a collective duty arises for this gene-editing solution. Moving towards the predation case, a collective duty and individual permissibility to herbivorize predators is attained. 



Bramble, B. (2021). Painlessly Killing Predators. Journal of Applied Philosophy 38 (2): 217-225.

Ebert, R. & Machan, T. (2012). Innocent Threats and the Moral Problem of Carnivorous Animals. Journal of Applied Philosophy, Vol. 29, No. 2, pp:146-159.

Regan, T. (1983). The Case for Animal Rights, Berkeley: University of California Press.


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I wonder what are feasible ways to feed predators cultivated meat? Maybe we could have robot prey that has cultivated meat on it. Though that would cost more until we have reached atomically precise manufacturing, though by that point we are also dealing with very powerful AI.