[Paleopsych] NS: Editorial: The trouble with human-animal chimeras
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Wed Jun 29 20:45:34 UTC 2005
Editorial: The trouble with human-animal chimeras
* 25 June 2005
LEON KASS, chairman of President Bush's bioethics council, calls it
"the wisdom of repugnance". Others know it simply as the "yuck factor"
- that visceral feeling that there is something wrong, even if you
cannot say what. That gut feeling, Kass argues, is telling you that a
moral boundary has been crossed and it is time to turn back.
The yuck factor has made more frequent appearances in recent years as
biotechnology has advanced. Most recently it has emerged in
discussions of human-animal chimeras - living entities that have both
human and animal cells. One researcher, for example, wants to create a
mouse with a brain composed entirely of human neurons. That might
sound like science fiction, and for now it is. But scientists have
already created similar human-animal amalgamations, and there are many
more on the drawing board.
Researchers' attraction to human-animal chimeras goes hand in hand
with the evolving field of stem cell therapies. They want to uncover
the potential of stem cells for both restoring health and destroying
it - which tissues stem cells can differentiate into, and whether they
will develop into tumours. This can only be tested by injecting human
stem cells into animals, which inevitably means creating chimeras.
Chimeras could also give us revolutionary new models of human diseases
such as cancer and Alzheimer's.
Animal rights campaigners are bound to see chimeras as yet another
example of unwarranted exploitation. While most people may not share
this view, and even though stem cells have extraordinary promise,
there is still something deeply unsettling about the prospect of
creating animals that are partly human. Explaining why, however, is
It cannot be just their "unnaturalness" - that they never existed
before humans decided to create them. After all, we have been
tinkering with the living world since prehistory, from hybrids to
recombinant DNA technology. Such creations are often controversial,
but they do not send us into a moral quandary.
There is no doubt that involving humans in experiments raises the
stakes: organ transplants and IVF certainly triggered deep moral
objections when they were introduced. Yet until recently, human-animal
chimeras have not done the same. Few are repulsed by the idea of
having a pig valve transplanted into their heart, or an injection of
pig neurons into their brain to treat Parkinson's disease, even though
both turn the recipients into chimeras.
But imagine if that injection of pig cells made its recipient less
human - if it made their thoughts and feelings a little bit pig-like.
That is an unsettling thought, and it reveals what is really troubling
about human-animal chimeras: the prospect of creating something that
is somehow sub-human, a person who is not quite human or one trapped
inside an animal's body. Where would such a creature belong in a world
used to clear distinctions - social, moral and legal - between humans
and other animals?
On present evidence, the chances of a mouse becoming conscious or
feeling human emotions are very slim. When human neural stem cells
were injected into a mouse brain they followed the rules for mouse
neural stem cells. It is likely that "humanness" resides not in
individual brain cells but in the organisation of those cells. One
curious consequence of these experiments is that they expose how
little we know about what it means to be human: they may even provide
The US National Academy of Sciences issued sensible guidelines earlier
this year to minimise the potential for "humanising" animals and vice
versa. That guidance calls for scientists to take extra precautions
when altering an animal's brain or germ line (lest future generations
grow ever more human). And it warns of the need to be alert to the
emergence of any human characteristics in animals - whether in
behaviour or appearance.
To reassure the public and ensure that animal experiments remain
acceptable, work on chimeras must be carefully monitored and limited
to tests that are essential to tackling human disease. Scientists
should also be specific about their purpose: if trials are basic
research, relevant only in the long-run, they should say so. There is
no room here for the "what would happen if I did this?" type of
experiment. The risk of creating a monster, provoking public anger and
destroying a field with huge potential benefit is just too great.
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