440   Koplin J,Wilkinson D. J Med Ethics 2019;45:440–446. doi:10.1136/medethics-2018-105227
Moral uncertainty and the farming of human-
pig chimeras
Julian Koplin,‍ ‍ 1,2
Dominic Wilkinson1,3,4
Feature article
To cite: Koplin J,Wilkinson D.
J Med Ethics
2019;45:440–446.
1
Murdoch Children’s Research
Institute, Parkville,Victoria,
Australia
2
University of Melbourne
Law School, Carlton,Victoria,
Australia
3
Oxford Uehiro Centre for
Practical Ethics, Faculty of
Philosophy, University of Oxford,
UK
4
John Radcliffe Hospital, Oxford,
UK
Correspondence to
Dr Julian Koplin, University of
Melbourne Law School, Carlton,
VIC 3053,Australia;
​koplinj@​unimelb.​edu.​au
Received 23 October 2018
Revised 13 March 2019
Accepted 3 April 2019
Published Online First
29 June 2019
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© Author(s) (or their
employer(s)) 2019. Re-use
permitted under CC BY.
Published by BMJ.
Abstract
It may soon be possible to generate human organs inside
of human-pig chimeras via a process called interspecies
blastocyst complementation.This paper discusses what
arguably the central ethical concern is raised by this
potential source of transplantable organs: that farming
human-pig chimeras for their organs risks perpetrating a
serious moral wrong because the moral status of humanpig
chimeras is uncertain, and potentially significant.
Those who raise this concern usually take it to be unique
to the creation of chimeric animals with ’humanised’
brains. In this paper, we show how that the same style
of argument can be used to critique current uses of nonchimeric
pigs in agriculture.This reveals an important
tension between two common moral views: that
farming human-pig chimeras for their organs is ethically
concerning, and that farming non-chimeric pigs for food
or research is ethically benign.At least one of these
views stands in need of revision.
It may soon be possible to grow human organs
inside human-pig chimeras via a technique known
as interspecies blastocyst complementation. This
technique involves two key processes. First, the
genes responsible for growing a specific organ
are knocked out of a pig embryo (eg, using
CRISPR-Cas9 genome editing). Second, human
pluripotent stem cells are injected into the pig
embryo, which is then implanted into a sow and
allowed to develop. The technique, if successful,
should create a part-human chimera—a creature
comprising cells from different embryonic origins.
Most of the chimera’s organs and tissues would
be composed of a mix of (mainly) pig and (some)
human cells. However, some specifically targeted
organs would be wholly human. Because the pig
embryo has been genetically altered to prevent the
growth of one or more specific organs, the human
stem cells should fill this ‘developmental niche’ to
grow functional human organs inside the chimeric
pig’s body.1
Organ generation via interspecies blastocyst
complementation is on the cusp of feasibility. Interspecies
blastocyst complementation has already
been used to generate rat organs inside rat-mouse
chimeras23
and,conversely,togeneratemouseorgans
inside mouse-rat chimeras.4
Scientists have even
achieved some success between humans and other
large mammals. A study recently published in Cell
has described the creation of human-pig chimeric
fetuses, which were created by introducing human
stem cells to pig embryos, implanting them into a
sow and allowing them to develop for 4 weeks. By
the end of this process, human cells could be found
throughout multiple tissues of the fetus. Although
significant practical obstacles remain before human
organs could be grown inside chimeric pigs, the
authors claim their success ‘raise[s] the possibility of
xeno-generating transplantable human tissues and
organs towards addressing the worldwide shortage
of organ donors.’5
Not only could this technique
help provide organs to those who would not otherwise
receive them, it might also circumvent the need
for lifelong immunosuppression. This is because
organs could theoretically be generated using stem
cells derived from the patients themselves, in which
case the organs would be a genetic match for their
intended recipient.6
This paper discusses what is arguably the
central ethical concern raised by the prospect of
generating human organs in human-pig chimeras:
that human-pig chimeras would develop morally
relevant cognitive capacities.i
This concern has
played a central role in both the broader bioethical
discussions of human-animal chimeras7 8
and
in recent public debates surrounding interspecies
blastocyst complementation.9
For example,
Lori Marino—writing in Stat—argued against
creating human-pig chimeras due to the risk that
such chimeras could develop highly sophisticated
cognitive capacities:
These organisms may be capable of self-awareness
to the extent that they understand their identity and
circumstances, which would produce unbearable
suffering… If we cannot say with certainty that this
will never happen, then we need to stop this kind
of research right now before we find ourselves in a
world where there is no line.10
Paul Knoepfler—writing in Wired—argued that
if human cells contribute to human-pig chimeras’
brains, the resulting creatures will occupy an ethical
‘grey zone’ between the moral status of animals
and humans. Although Knoepfler suggested these
concerns could theoretically be mitigated by limiting
human cells’ contribution to chimeric animals’
brains, he argued that an appropriate threshold will
be extremely difficult to define:
There's no clear dividing line on the question of
‘overly’ human chimeric brains because we lack an
understanding of at what point ‘humanization’ of an
animal brain could lead to more human-like thought
or consciousness. We don't even know when this
happens in the normal developing human brain.11
i 
Using human-pig chimeras to generate human
organs also raises concerns about animal welfare,
the ‘unnaturalness’ of crossing species boundaries
and the risk of transmitting novel infections with
the transplantable organs.21
These issues fall outside
the scope of this paper.
441Koplin J,Wilkinson D. J Med Ethics 2019;45:440–446. doi:10.1136/medethics-2018-105227
Feature article
Julian Savulescu has argued that human-pig chimeras should
be treated according to the highest level of moral status they
could plausibly possess. This would require us to treat human-pig
chimeras as if they have high moral status until they are proven
to lack cognitive abilities beyond those of regular, non-chimeric
pigs:
In the absence of conclusive research on these questions, any such
chimera should be accorded the highest moral status consistent
with its likely nature…. [I]f it could plausibly have higher cognitive
functions, it should be treated as if it would have them. In
considering the new life forms we create, we should err on the side
of sympathy and generosity.12
Policy discussions of human-animal chimeras (including, but
not limited to, chimeras created via blastocyst complementation)
are likewise dominated by the concern that animals with
chimeric brains might develop human-like cognitive capacities.8
Groups including the UK Academy of Medical Sciences,13
Japanese
Expert Panel on Bioethics14
and German Ethics Council15
have recommended that research involving chimeric animals
with humanised brains should be subject to greater restrictions
than other forms of chimera research. In the USA, the National
Institutes of Health has issued a moratorium on funding for blastocyst
complementation as it considers ethical issues raised by
the prospect of human cells contributing to chimeric animals’
brains.16
Concerns about chimeric animals’ moral status are
most commonly and most forcefully raised regarding brain
chimera research involving non-human primates17 18
or other
large mammals,13
although some argue that we should not create
any chimeras with human-like neuronal structures, regardless
of species, due to concerns that such animals would develop
human-like consciousness.19
Although there is limited bioethical
work specifically on the creation of human-pig chimeras
via blastocyst complementation, the literature that does exist
often recommends creating safeguards against the humanisation
of chimeric animals’ brains to ensure these creatures do not
develop human-like thought or consciousness.1 20 21
This paper highlights an important tension between this trepidation
regarding the farming of human-pig chimeras as a source
of transplantable organs and the current widespread acceptance
of the farming of non-chimeric pigs as a source of food. We argue
below that ethical concerns about the creation of human-pig
chimeras with partly humanised brains are best understood in
terms of the uncertain moral status of these chimeric animals.
We further show that the same factors that render uncertain the
moral status of human-pig chimeras also render uncertain the
moral status of regular, non-chimeric pigs. There is therefore
an important inconsistency between many people’s attitudes
towards the farming of human-pig chimeras and the farming of
non-chimeric pigs. Either the creation of human-pig chimeras
via blastocyst complementation is less morally concerning than
is commonly assumed, or the use of non-chimeric pigs in livestock
is more morally concerning than is commonly assumed—
or possibly both.
First, however, it is worth clarifying what we mean when we
discuss the moral status of human-pig chimeras and regular,
non-chimeric pigs. To say that a being has moral status is to say
that a being has moral importance in their own right; beings with
moral status have interests that ought to be taken into account
when we consider how we should treat them. We assume that
moral status can be ascribed in degrees. To say that one being
has more moral status than another is to say that our moral
obligations towards the first being are weightier than our moral
obligations towards the second. Depending on one’s philosophical
commitments, moral status might be thought to vary because
some kinds of beings deserve greater moral consideration than
others, or it might vary because of differences in the nature and
strength of different kinds of beings' interests.22
We believe the
kinds of concerns about human-pig chimera research discussed
above are most naturally expressed as concerns about chimeric
animals’ degree of moral status. The concern seems to be that
human-pig chimeras could develop characteristics that increase
their moral status beyond that of a regular pig, potentially even
to the point that their moral status approaches that of a regular
human adult.
The arguments of this paper are also compatible with the view
that full moral status is a threshold concept—that is, that it is
a feature of beings who have at least a threshold level of some
capacity or set of capacities.23
For those who view moral status
this way, the concern about human-pig chimeras is that there is
a non- probability that some of these animals might cross the
threshold to full moral status.
We would also like to assuage a possible concern about this
paper’s motivation. It might seem unusual, or even flippant,
for an analysis of the ethics of chimera research to segue into
a discussion of the ethics of eating meat. Unusualness aside, we
think our argument has important practical implications. If our
argument is correct, we either need to become more accepting
of (and impose fewer restrictions on) the creation of part-human
chimeras with humanised brains, or else become less accepting of
(and impose greater restrictions on) the farming of non-human
animals for food. Either approach will require us to rethink
important human practices.
We also have a second aim that is more concretely tied to
current bioethical controversies regarding part-human chimeras.
By highlighting a problem with current ethical thought regarding
human-pig chimeras, we hope to prevent this problem from slipping
unnoticed into (and potentially distorting) future ethical
analysis of part-human chimera research. Our second aim, in
other words, is to help clear the intellectual space required to
untangle the ethical issues raised by part-human chimeras.
Moral uncertainty regarding human-pig chimeras
It is widely believed that our moral obligations towards
non-human animals depend partly on their cognitive abilities,
with the interests of humans privileged over those of non-human
animals because humans typically possess some unique set of
morally relevant cognitive capacities. On this view, if a parthuman
chimera acquires whatever set of cognitive capacities
undergird humans’ moral status, it would also acquire the same
degree of moral status we usually afford humans. It would be
gravely wrong to treat humans in many of the ways we currently
treat animal research subjects, or to raise and slaughter humans
for their organs. By extension, it would be gravely wrong to use
human-pig chimeras in research, or to use them as a source of
transplantable organs, if these chimeric animals acquire cognitive
capacities that confer human-like moral status.
The moral permissibility of generating human organs inside of
human-pig chimeras therefore turns, in large part, on the moral
status of these chimeric animals. The problem is that determining
a human-pig chimera’s moral status would be very difficult. The
first difficulty is philosophical. In order to accurately determine
the moral status of a human-pig chimera we would first need
to know precisely what capacities confer what degree of moral
status. But this, of course, remains a major unresolved question
in moral philosophy. The second difficulty is epistemological.
442 Koplin J,Wilkinson D. J Med Ethics 2019;45:440–446. doi:10.1136/medethics-2018-105227
Feature article
Once we determine what capacities confer what degree of moral
status, we will need to devise some way of testing for these
capacities in chimeric animals that look, behave and communicate
very differently to humans. There are many reasons why
this would be difficult to achieve, including because we cannot
speak with human-pig chimeras directly, because human-pig
chimeras’ cognition would likely be influenced by their embodiment
in porcine bodies and the conditions under which they
are raised, and because inferences drawn from animal behaviour
or physiology are often open to question.24
The moral status of
human-pig chimeras is therefore doubly uncertain. We would
be uncertain of what cognitive capacities such chimeras possess,
and we would further be uncertain of what set of capacities are
relevant to its moral status.
Perhaps this conclusion is too quick. It is sometimes argued
that even if chimeric animals have the latent ability to develop
morally relevant cognitive abilities, the animal would need to be
raised under the ‘right’ set of social conditions for these abilities
to develop. Given that laboratory conditions are unlikely to
provide the necessary forms of interaction and socialisation (and
given, moreover, that human-pig chimeras could be killed while
they are still quite young), we should not be overly concerned
about chimeric animals’ moral status.24 25
Or so the argument
goes.
To see where this argument goes wrong, consider the following
thought experiment:
Infant organ harvesting: It is 2040. The problem of shortage of
kidneys for transplantation has been solved. Patients who have
kidney failure have stem cells harvested. Those cells are then
inoculated into a human fetus that has been modified via CRISPR
technology to knock out the genes that normally drive development
of that organ. The fetus is gestated in a surrogate, born alive and
then euthanised at a few minutes of age.
Presumably, virtually no one would accept infant organ
harvesting. While the infant’s cognitive capacities are not those
of a fully grown human, they would develop further if they had
not been killed. Killing the infant before they have a chance to
manifest or develop more sophisticated self-awareness, communication
or relationships would not mitigate or remove the
wrongness of killing them. If these factors do not mitigate the
wrongness of killing an infant, they cannot mitigate the wrongness
of killing human-pig chimeras who also would have gone on
to develop morally relevant cognitive capacities.
What should we do if we are uncertain about the degree of
moral status possessed by human-pig chimeras? We would make
a grave moral mistake if human-pig chimeras have a high degree
of moral status and we mistakenly treat them as if they have only
the lower degree of moral status that is commonly attributed to
non-chimeric pigs. In particular, if human-pig chimeras possess
a degree of moral status that is equivalent (or very close) to that
of a normal human, then killing them for their organs would be
morally equivalent (or very close to equivalent) to infant organ
harvesting. We should therefore be confident that human-pig
chimeras would lack morally relevant cognitive capacities before
setting out to use them as a source of transplantable human
organs.ii
This leaves open the question of how confident we should
be before setting out to use human-pig chimeras a source of
ii 
This is consistent with the view—defended by Harry Brad-
shaw,39
Simon Knutsson and Christian Munthe,40
and Jeff
Sebo41
—that if we are uncertain of some being’s moral status,
we ought to treat them as having at least partial moral status.
transplantable organs. One way of unpacking this question
would be to imagine that there is some probability X that the
chimeric animals have cognitive capacities that are equal to
cognitively normal humans, and that the wrongness of killing
them would be equivalent to the killing of a child to harvest
their organs. The question, then, is what value of X would be
sufficiently low for generating chimeras to be acceptable?
Here is another thought experiment:
Low probability infant organ harvesting: It is 2060. The problem
of shortage of kidneys for transplantation has been solved. Patients
who have kidney failure have stem cells harvested. Those cells are
then inoculated into a pig fetus. This is highly likely to generate a
viable organ for transplantation, and research has been done that
unequivocally shows that the chimeric pigs have no human neural
tissue. However, in X% of cases, no viable pig organ is able to
be generated. In such a situation, a human fetus is used instead.
The human fetus is gestated in a surrogate, born alive and then
euthanased at a few minutes of age.
Those who hold strong deontological views might hold that
farming human-pig chimeras would be morally impermissible
unless X is zero. A consequentialist might set the threshold
for X somewhat higher, given that the harms to human infants
would need to be balanced against the potential benefits we
might achieve by generating organs in this way. Exactly where
a consequentialist should set X is, of course, an open question.
In general, however, given that most people would find it highly
unethical to harvest organs from normal human children, most
people would presumably set the value of X quite low.
The above argument should be relatively uncontroversial.
Indeed, something like the moral uncertainty argument is
regularly offered as a reason to ensure that human cells do not
contribute to the brains of human-pig chimeras created via interspecies
blastocyst complementation (see eg, refs 1 20 21).iii
 Similarly,
the broader literature on part-human chimeras generally
concurs with the view that chimeras with humanised brains raise
greater ethical concerns than other areas of chimera research,
especially in cases where the host animal is closely related to
humans8 18
—concerns that are presumably also based on the
uncertain moral status of these chimeric animals. The problem
is that the moral uncertainty argument does not only apply to
human-animal chimeras with humanised brains. As we show
below, we also have good reason to view the moral status of
non-chimeric pigs as highly uncertain.
Moral uncertainty regarding non-chimeric pigs
It is difficult to assess the cognitive abilities of pigs. Since we
cannot communicate with pigs directly, we are limited to drawing
inferences from pig behaviour and physiology. Some research
has been conducted into pig cognition, and while it is unclear
exactly what inferences we should draw from the relevant findings,
this research provides ample reason to take pigs’ cognitive
abilities seriously. Pigs react to the emotional state of other
pigs, suggesting a capacity for empathy. Pigs have been trained to
comprehend a basic language combining symbols for actions and
objects (eg, ‘fetch the frisbee’). Some (non-chimeric) pigs are able
iii 
This leaves open the question of whether it is ethically permissible
to create chimeric animals with humanised brains to study
and/or develop new treatments for neurodegenerative disorders
(see eg, ref 42). It is obviously impossible to conduct such forms
of research without creating chimeric animals with humanised
brains.
443Koplin J,Wilkinson D. J Med Ethics 2019;45:440–446. doi:10.1136/medethics-2018-105227
Feature article
to manipulate a modified joystick to align an on-screen cursor
with a specific target, which arguably suggests self-awareness
and self-agency. Finally, pigs have been documented behaving in
ways that suggest sophisticated forms of social cognition.26
This
last category of research has revealed some particularly striking
behaviours. Consider a study that tasked pairs of pigs with
foraging together daily in a specially designed arena. The smaller
pig learnt the location of the food in advance, whereas the larger
pig did not. After multiple sessions the larger pig usually began
to follow their pair-mate to the food, then push them aside to
claim the meal for themselves. In other words, the larger pig
appeared to realise their pair-mate knew something they did
not, then used this knowledge to exploit their pair-mate. After
further foraging sessions the smaller pig would not head to the
food until their partner was distant, out of sight, or otherwise
occupied, apparently manipulating their pair-mate in order to
keep the meal for themselves.27
It is difficult to know exactly what to make of such findings.
On the one hand, there is a risk we might err on the side of
anthropomorphic bias and mistake behaviours grounded in
relatively unsophisticated cognitive processes as evidence of a
sophisticated, human-like mind. On the other hand, we might
make the opposite mistake—one that Frans de Waal has labelled
‘anthropodenial’28
—and mistakenly assume these behaviours
are properly explained in terms of less sophisticated cognitive
abilities than pigs actually possess. Until we work out how to
strike the right balance, and pending further research into pigs’
cognitive abilities, the nature and sophistication of pigs’ cognitive
abilities will remain an open question.
Not only are the cognitive abilities of pigs uncertain, so too
is the moral salience of whatever cognitive abilities pigs actually
do possess. There are many philosophical accounts of the
grounds of moral status. Some accounts are unlikely to be met
by non-chimeric pigs. For example, Insoo Hyun claims full
moral status is conferred by human self-consciousness—understood
as a kind of higher order mental awareness of one’s own
mental experiences—which Hyun believes requires a facility
for language unique to humans.24
Other plausible baselines for
moral status are based on characteristics that might be shared
by at least some non-human animals, such as sentience, agency,
autonomy, self-awareness, rationality, moral agency and sociability.
It seems likely that pigs would have a high degree of moral
status on at least some of these accounts. Indeed, some plausible
baselines for moral status—such as sentience—are relatively
undemanding, and are almost certainly met by pigs. Until
we work out which account of moral status to apply, the moral
salience of pigs’ cognitive abilities will be uncertain even if we
can determine what cognitive abilities pigs typically possess.
The moral uncertainty argument against growing human
organs in human-pig chimeras and the moral uncertainty argument
against farming pigs for food are not perfectly analogous.
On the one hand, it is possible that human-pig chimeras would
develop greater cognitive abilities than non-chimeric pigs due
to the contribution of human cells to the chimeric pigs’ brains;
accordingly, human-pig chimeras may be more likely to possess
full moral status than regular pigs. In this respect, farming
human-pig chimeras with partly humanised brains might be
ethically riskier than farming non-chimeric pigs. But on the
other hand, the creation of human-pig chimeras aims to satisfy
a morally weighty goal—that is, to save lives—whereas farming
pigs to produce meat serves only to satisfy some people’s culinary
preferences. Satisfying culinary preferences is significantly
less morally important than saving lives. In this respect,
farming pigs for food is ethically riskier than farming human-pig
chimeras to provide organs for transplant. Given this difference
in the moral stakes, it seems that the moral uncertainty argument
should weigh at least as strongly against the farming of
non-chimeric pigs for meat as it weighs against the farming of
human-pig chimeras for their organs.
It seems, then, that two widely held moral views are inconsistent
with each other. On the one hand, the uncertain moral
status of human-pig chimeras is thought to provide a significant
moral consideration against pursuing such research, or at
least in favour of moving forward cautiously (eg, by ensuring
human cells do not make a meaningful contribution to chimeric
pigs’ brains). On the other hand, the uncertain moral status of
non-chimeric pigs is rarely recognised as a compelling reason to
stop farming them. The question, then, is how this tension ought
to be resolved.
Resolving the tension
Many people endorse a precautionary approach to human-pig
chimera research because of concern about the possibility that
such animals have sufficient moral status that killing them is a
serious moral wrong. (For simplicity, we refer to quality as ‘full
moral status.’) This might be called the moral status precautionary
principle (MSPP).
Moral status precautionary principle: A course of action should not
be pursued if there is a reasonable fear that the course of action will
cause serious harm to beings of full moral status, even if there is
no conclusive evidence that the beings will actually have full moral
status.
Like other versions of the precautionary principle, the MSPP
faces a distinctive challenge.29 30
The challenge runs as follows. It
is possible to imagine scenarios where both pursuing a course of
action and failing to pursue the same course of action will trigger
the precautionary principle (in the case of the MSPP, by risking
serious harm to beings of full moral status). In such contexts, the
precautionary principle leads to the paradoxical conclusion that
it would be wrong to pursue and to fail to pursue a particular
course of action. For this reason, some philosophers hold that
precautionary principles are incoherent.
This objection is not necessarily fatal to the MSPP. Proponents
of other kinds of precautionary principle have argued that this
objection can be met by more carefully specifying the conditions
under which the precautionary principle applies—for example,
by specifying that the principle applies only to threats of a particular
magnitude and probability, or by developing mechanisms to
ensure precautionary measures are proportional to the size of
the threat.31 32
A similar response might be open to proponents
of the MSPP.
Alternatively, one could reject the MSPP and endorse the
less demanding moral status no alternative principle (MSNAP),
which would allow the farming of human-pig chimeras only if
there are no alternative means of addressing the organ shortage:
Moral status no alternative principle: A course of action may be
pursued if there is a reasonable fear that the course of action will
cause serious harm to beings of full moral status, only if there is no
alternative course of action that would achieve the same benefit
without any risk of serious harm to beings of full moral status.iv
iv 
The MSNAP resembles a well-established principle in animal
ethics: that it is permissible to conduct harmful forms of animal
research only if there is no alternative way to answer the scientific
question.43
444 Koplin J,Wilkinson D. J Med Ethics 2019;45:440–446. doi:10.1136/medethics-2018-105227
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Neither the MSPP nor the MSNAP necessarily captures the
complete moral picture. The underlying moral question at play
is about how we should approach decision-making when we are
unsure about moral facts salient to a decision. The MSPP and
MSNAP are not the only, nor necessarily the best, approaches
one could take.v
However, we think they are nonetheless a
good approximation of the kinds of intuitions that underlie
many people's reluctance to inflict serious harms on human-pig
chimeras with humanised brains. The MSPP and the MSNAP
will therefore suffice for the purposes of this paper.
Both the MSPP and the MSNAP are consistent with the view
that we should require confidence that human-pig chimeras
would lack full moral status before using them to grow transplantable
human organs. But if one accepts the MSPP or
MSNAP in relation to human-pig chimeras, then one also ought
to accept these principles in relation to regular, non-chimeric
pigs. Given that there is a plausible alternative to farming
pigs for food (vegetarianism), this would seem to entail that
we renounce the farming of pigs for food. Conversely, if one
accepts the farming of non-chimeric pigs for food (and therefore
rejects the MSPP/MSNAP’s application to regular pigs),
then one should presumably also reject the MSPP/MSNAP’s
application to human-pig chimeras. How, then, should we bring
our views into alignment?
One approach is to reject the precautionary principle’s application
to either human-pig chimeras or non-chimeric pigs.
One might hold that the cognitive capacities associated with
full moral status are fleetingly unlikely to emerge in anything
other than a fully human brain that is housed in a fully human
body. Indeed, some commentators have made precisely this
argument to attempt to defuse concerns about human-animal
chimeras’ moral status.24 33
This view does not give rise to the
kind of tension described in this paper. Rather than singling out
human-pig chimeras for special moral concern, it denies that
either human-pig chimeras or non-chimeric pigs could plausibly
possess a substantial degree of moral status.
Is this a satisfactory way to harmonise our views on the moral
status of pigs and human-pig chimeras? It is at least superficially
attractive, not least because it preserves deeply ingrained
intuitions that our current uses of non-human animals are
ethically appropriate. However, we may have good reason to
treat these intuitions with suspicion. There is a burgeoning
body of literature that suggests our estimation of non-human
animals’ moral status is highly flexible and, importantly, shaped
by whether or not we classify a particular animal as food.34
Consider, for example, a study in which students were asked to
sample a certain kind of food (either beef jerky or cashew nuts)
and then—for what appeared to be an unrelated project—
asked their opinions of the cognitive capacity and moral status
of a range of animal species. Those who were assigned to the
beef jerky group were more inclined to deny that food animals
are due moral consideration than those students assigned to
the cashew nut group.35
Our willingness to eat pigs might not
follow from a considered judgement that pigs lack morally
relevant cognitive capacities; instead, our judgement that pigs
lack morally relevant cognitive capacities might be distorted by
psychological mechanisms we use to render our consumption
of them more palatable.
v 
For a general discussion of decision-making under moral uncertainty,
see ref 44. For a broader overview of different ways one
could respond to uncertainty regarding moral status, see ref 41.
A second possible solution is to apply the MSPP/MSNAP to
both human-pig chimeras and non-chimeric pigs. If we think it
is appropriate to take precautions against harming human-pig
chimeras on the chance they have full moral status, then perhaps
we should also be prepared to take precautions against harming
regular pigs on the chance they possess full moral status. This
would require us to renounce the farming of pigs for food unless
and until we can be confident that pigs lack more than minimal
moral status.
On balance, we think this second approach is more promising
than the first. We have good reason to be wary of our
intuitions regarding the moral status of non-chimeric pigs, for
(as outlined above) our intuitions may be shaped by a powerful
bias against attributing sophisticated cognitive abilities to pigs
or according them moral status. In comparison, our moral
views on human-pig chimeras—a new type of creature which
would presumably not be regarded as food, and which is not yet
enmeshed in any culturally valued practices—are presumably
not be subject to the same bias. Arguably, then, we have good
reason to view the moral status of both chimeric and non-chimeric
pigs as uncertain, and to apply the MSPP/MSNAP to both
kinds of beings.
There is one further possibility. Perhaps both sets of attitudes
require revision. We might be liable to overestimate the
moral status of human-pig chimeras (because they are part
human) and also liable to underestimate the moral status of
regular pigs (because they are not). Perhaps concerns about the
moral status of both human-pig chimeras should be considered
somewhat less pressing than is commonly assumed, whereas
concerns about the moral status of non-chimeric pigs should
be considered somewhat more pressing than is commonly
assumed.
In any case, this paper’s primary aim has been to highlight an
important tension between two widely held moral views, not to
definitely resolve that tension. Exactly how we should realign
our views is open for further debate; we have mainly sought
to highlight a tension in existing ethical thought that we think
needs to be resolved.
Possible objections
We can see two potential objections to our argument.vi
These
objections attempt to show that only human-pig chimeras (and
not regular pigs) have uncertain moral status—in which case one
could consistently hold that farming human-pig chimeras raises
serious moral concerns, whereas farming regular pigs does not.
In this section we show how each objection can be met.
The first objection runs as follows. We have argued that those
who apply the MSPP/MSNAP to the farming of human-pig
chimeras should also apply the same principle to the farming
of non-chimeric pigs. But human-pig chimera research has a
unique feature: it raises the possibility of raising the animals’
cognitive abilities above the level of regular pigs. On this view,
there is no inconsistency in holding that the moral status of
human-pig chimeras is uncertainwhile also holding that regular
pigs are certain to possess no more than a negligible degree of
moral status. Perhaps the reason why many people accept the
farming of non-chimeric pigs (but nonetheless find the farming
of human-pig chimeras morally troubling) is because they are
vi 
We thank two anonymous peer reviewers for raising these
objections and pressing us to respond.
445Koplin J,Wilkinson D. J Med Ethics 2019;45:440–446. doi:10.1136/medethics-2018-105227
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already certain that non-chimeric pigs lack sufficient moral
status that killing them is a serious moral wrong.
We do not think this is a tenable view. To defend it, one
would have to pinpoint some morally relevant feature(s) that
human-pig chimeras could plausibly develop but that non-chimeric
pigs certainly lack. This would be a very difficult task.
As highlighted earlier, there is both significant philosophical
disagreement regarding the grounds of moral status and significant
scientific disagreement regarding the nature and sophistication
of pig cognition. It is philosophically difficult—potentially
far more difficult than many people realise—to pinpoint some
set of cognitive capacities that can do the necessary moral work.
Moreover, there is considerable philosophical debate and argument
that advances the view that non-chimeric pigs do possess
capacities that merit moral consideration.36 37
Given this debate,
it appears difficult to defend a view that pigs certainly lack
moral status. We suggest that anyone familiar with debates about
animal ethics ought to admit there is at least a non-trivial possibility
that (non-chimeric) pigs have cognitive capacities meriting
moral consideration.
Perhaps we can dissolve the moral tension by linking moral
status to something other than a being’s cognitive capacities.
Perhaps what motivates concerns about chimeric animals’ moral
status is not that they possess sophisticated cognitive capacities,
but that they are partly human. In other words, one might think
that (full) moral status depends on what species one belongs
to rather than the cognitive capacities one happens to possess.
In line with this view, the moral status of human-pig chimeras
might be uncertain because they are neither fully human nor
fully non-human. The moral status of regular pigs, however, is
easy to settle; regular pigs are entirely non-human and therefore
certainly lack (full) moral status. Accordingly, those who
think that humanness is what confers (full) moral status might
deny that the MSPP/MSNAP weighs against the farming and
consumption of regular, non-chimeric pigs.vii
There are two reasons we do not think this objection succeeds.
First, the idea that humanness confers moral status seems to play
little role in current debates about the generation of human
organs in chimeric animals. If concerns about interspecies blastocyst
complementation were based on the blurring of species
boundaries, they would presumably apply regardless of whether
the chimeric animal develops unexpected cognitive abilities.
However, the literature surveyed at the beginning of this paper
suggests that interspecies blastocyst complementation is controversial
primarily because of the risk that human cells would
contribute to the brain and thereby affect the chimeric animal’s
cognition. Indeed, one common suggestion made throughout
this literature—that we should limit the degree of chimerism in
(some) chimeric animals’ brains—would make little sense if one
thought that introducing human cells per se renders chimeric
animals’ moral status uncertain. A pig with a human pancreas
is not entirely non-human, even if human cells are absent from
the rest of its body. However, few commentators have suggested
that possessing a human pancreas could increase the moral status
of a pig beyond that of its regular, non-chimeric counterparts.
In much the same vein, few people believe that humans who
vii 
One might still think that harming pigs might coarsen human
attitudes towards other humans, display a lack of virtue, or be
wrong for some other reason. But denying that pigs have (full)
moral status voids the most central criticism against practices
that harm pigs—which is that these practices are wrong by virtue
of the harms inflicted on the pigs themselves.
receive a porcine heart valve replacement risk diluting their own
moral status.
But more importantly, there are good philosophical reasons
to doubt that species membership is relevant to moral status.
Consider the following thought experiment from David
DeGrazia. DeGrazia describes the recent discovery of what is
thought to be a distinct hominid species—Homo floresiensis—
that seem to have developed and used sophisticated tools.
Using H. floresiensis as an example, DeGrazia asks whether we
should ascribe (full) moral status to non-human hominid species
that possess cognitive abilities similar to those of present-day
humans. The answer, presumably, is yes. But if this is the case,
species membership per se must be irrelevant to moral status:
[T]o deny that these hominids—or beings like them and like us—
lack(ed) moral status merely because of species difference is the
height of bigotry. Even if biology were so morally important—and
it isn’t—there would be no reason to think that species markers are
so important to moral status. After all, these recent hominids…
were members of our genus, Homo. And all members of the genuses
Australopithecus and Paranthropus were, like members of Homo,
hominids, another biological grouping. And, of course, all of these
and many other animals are apes, primates, mammals, vertebrates,
and so on. To single out species as the unique biological basis for
moral status is as silly intellectually as it is self-serving for those in
whom species prejudice operates strongly.38
If we are to ascribe moral status to some beings and not to
others, we will need to appeal to some feature other than species
membership. The answer, presumably, lies in the mental life of
the being in question. But if we are to ascribe moral status on the
basis of a being’s cognitive capacities, we will need to confront
the possibility that beings other than humans—including pigs—
have the requisite set of morally relevant characteristics.viii
Conclusion
We have argued that two common moral views are in tension
with each other. On the one hand, it is widely believed that the
creation of human-pig chimeras with partly humanised brains
would raise weighty moral concerns, largely because the moral
status of such animals would be uncertain. On the other hand,
it is widely believed that our current use of non-chimeric pigs
as livestock is morally benign. In both cases, however, there are
grounds for moral uncertainty. First, we are faced with difficult
viii 
Even if one agrees that the moral uncertainty argument leads
to the right conclusions regarding human-pig chimeras and
non-chimeric pigs, one might worry that this argument has unpalatable
implications for the abortion debate. Like the farming of
human-pig chimeras and regular pigs, abortion involves killing
a being that at least some moral views grant full moral status. 
We do not think our argument has problematic implications
for the ethics of abortion. Of the two moral principles we have
been considering, only the MSPP might weigh against abortion.
The MSPP would rule out abortion if there is reasonable
fear that, by terminating a pregnancy, one would inflict
serious harm on a being of full moral status. Some philosophers
have offered arguments to this effect,45
but whether
such arguments succeed is beyond the scope of this paper. 
The MSNAP applies only if there is some alternative course of
action that would achieve one’s ends without risking serious
harm to beings of full moral status. In the case of abortion, no
such alternative is available; one cannot achieve the goal of
respecting a woman’s wish not to continue a pregnancy without
ending the life of the fetus. Accordingly, the MSNAP does not
support any specific position on the ethics of abortion.
446 Koplin J,Wilkinson D. J Med Ethics 2019;45:440–446. doi:10.1136/medethics-2018-105227
Feature article
questions regarding what set of cognitive capacities are morally
relevant. Second, we are faced with the difficulty of testing
for these capacities in creatures that look very different to us,
that behave in very different ways and that we cannot communicate
with directly. It is a problem, then, that currently only
the farming of human-pig chimeras currently seems to attract
serious moral concern. Until we resolve this inconsistency our
treatment of human-pig chimeras and/or non-chimeric pigs will
almost certainly rest on a serious moral mistake.
Contributors  JK devised the project and took the lead in writing the manuscript.
DW provided critical feedback and contributed to writing the manuscript.
Funding  JK and DW, through their involvement with the Murdoch Children’s
Research Institute, received support from the Victorian State Government through
the Operational Infrastructure Support (OIS) Program. DW was supported for this
work by a grant from the Wellcome trust (WT106587/Z/14/Z.) DW would also like to
acknowledge the generous support of the Russell and Mab Grimwade Miegunyah
Fund; part of this work was undertaken while he was a Miegunyah distinguished
visiting research fellow at the University of Melbourne.
Competing interests  None declared.
Provenance and peer review  Not commissioned; externally peer reviewed.
Open access  This is an open access article distributed in accordance with the
Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits
others to copy, redistribute, remix, transform and build upon this work for any
purpose, provided the original work is properly cited, a link to the licence is given,
and indication of whether changes were made. See: https://​creativecommons.​org/​
licenses/​by/​4.​0/.
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