[Paleopsych] NS: Editorial: The trouble with human-animal chimeras

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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
    some answers.

    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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