[Paleopsych] Natl Geog: Animal-Human Hybrids Spark Controversy
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Tue Feb 8 21:47:32 UTC 2005
Animal-Human Hybrids Spark Controversy
January 25, 2005
[I'm taking my annual Lenten break from forwarding articles again this
year. It's a vice to spend so much time doing this. So I'll be off the air
for forty days and forty nights from Ash Wednesday until Easter.]
Scientists have begun blurring the line between human and animal by
producing chimeras--a hybrid creature that's part human, part animal.
Chinese scientists at the Shanghai Second Medical University in 2003
successfully fused human cells with rabbit eggs. The embryos were
reportedly the first human-animal chimeras successfully created. They
were allowed to develop for several days in a laboratory dish before
the scientists destroyed the embryos to harvest their stem cells.
In Minnesota last year researchers at the Mayo Clinic created pigs
with human blood flowing through their bodies.
And at Stanford University in California an experiment might be done
later this year to create mice with human brains.
Scientists feel that, the more humanlike the animal, the better
research model it makes for testing drugs or possibly growing "spare
parts," such as livers, to transplant into humans.
Watching how human cells mature and interact in a living creature may
also lead to the discoveries of new medical treatments.
But creating human-animal chimeras--named after a monster in Greek
mythology that had a lion's head, goat's body, and serpent's tail--has
raised troubling questions: What new subhuman combination should be
produced and for what purpose? At what point would it be considered
human? And what rights, if any, should it have?
There are currently no U.S. federal laws that address these issues.
The National Academy of Sciences, which advises the U.S. government,
has been studying the issue. In March it plans to present voluntary
ethical guidelines for researchers.
A chimera is a mixture of two or more species in one body. Not all are
considered troubling, though.
For example, faulty human heart valves are routinely replaced with
ones taken from cows and pigs. The surgery--which makes the recipient
a human-animal chimera--is widely accepted. And for years scientists
have added human genes to bacteria and farm animals.
What's caused the uproar is the mixing of human stem cells with
embryonic animals to create new species.
Biotechnology activist Jeremy Rifkin is opposed to crossing species
boundaries, because he believes animals have the right to exist
without being tampered with or crossed with another species.
He concedes that these studies would lead to some medical
breakthroughs. Still, they should not be done.
"There are other ways to advance medicine and human health besides
going out into the strange, brave new world of chimeric animals,"
Rifkin said, adding that sophisticated computer models can substitute
for experimentation on live animals.
"One doesn't have to be religious or into animal rights to think this
doesn't make sense," he continued. "It's the scientists who want to do
this. They've now gone over the edge into the pathological domain."
David Magnus, director of the Stanford Center for Biomedical Ethics at
Stanford University, believes the real worry is whether or not
chimeras will be put to uses that are problematic, risky, or
Human Born to Mice Parents?
For example, an experiment that would raise concerns, he said, is
genetically engineering mice to produce human sperm and eggs, then
doing in vitro fertilization to produce a child whose parents are a
pair of mice.
"Most people would find that problematic," Magnus said, "but those
uses are bizarre and not, to the best of my knowledge, anything that
anybody is remotely contemplating. Most uses of chimeras are actually
much more relevant to practical concerns."
Last year Canada passed the Assisted Human Reproduction Act, which
bans chimeras. Specifically, it prohibits transferring a nonhuman cell
into a human embryo and putting human cells into a nonhuman embryo.
Cynthia Cohen is a member of Canada's Stem Cell Oversight Committee,
which oversees research protocols to ensure they are in accordance
with the new guidelines.
She believes a ban should also be put into place in the U.S.
Creating chimeras, she said, by mixing human and animal gametes
(sperms and eggs) or transferring reproductive cells, diminishes human
"It would deny that there is something distinctive and valuable about
human beings that ought to be honored and protected," said Cohen, who
is also the senior research fellow at Georgetown University's Kennedy
Institute of Ethics in Washington, D.C.
But, she noted, the wording on such a ban needs to be developed
carefully. It shouldn't outlaw ethical and legitimate
experiments--such as transferring a limited number of adult human stem
cells into animal embryos in order to learn how they proliferate and
grow during the prenatal period.
Irv Weissman, director of Stanford University's Institute of
Cancer/Stem Cell Biology and Medicine in California, is against a ban
in the United States.
"Anybody who puts their own moral guidance in the way of this
biomedical science, where they want to impose their will--not just be
part of an argument--if that leads to a ban or moratorium. ... they
are stopping research that would save human lives," he said.
Mice With Human Brains
Weissman has already created mice with brains that are about one
Later this year he may conduct another experiment where the mice have
100 percent human brains. This would be done, he said, by injecting
human neurons into the brains of embryonic mice.
Before being born, the mice would be killed and dissected to see if
the architecture of a human brain had formed. If it did, he'd look for
traces of human cognitive behavior.
Weissman said he's not a mad scientist trying to create a human in an
animal body. He hopes the experiment leads to a better understanding
of how the brain works, which would be useful in treating diseases
like Alzheimer's or Parkinson's disease.
The test has not yet begun. Weissman is waiting to read the National
Academy's report, due out in March.
William Cheshire, associate professor of neurology at the Mayo
Clinic's Jacksonville, Florida, branch, feels that combining human and
animal neurons is problematic.
"This is unexplored biologic territory," he said. "Whatever moral
threshold of human neural development we might choose to set as the
limit for such an experiment, there would be a considerable risk of
exceeding that limit before it could be recognized."
Cheshire supports research that combines human and animal cells to
study cellular function. As an undergraduate he participated in
research that fused human and mouse cells.
But where he draws the ethical line is on research that would destroy
a human embryo to obtain cells, or research that would create an
organism that is partly human and partly animal.
"We must be cautious not to violate the integrity of humanity or of
animal life over which we have a stewardship responsibility," said
Cheshire, a member of Christian Medical and Dental Associations.
"Research projects that create human-animal chimeras risk disturbing
fragile ecosystems, endanger health, and affront species integrity."
An ancient Etruscan statue of a chimera found in north-central Italy.
The mythic beast had a lion's body, serpent's tail, and goat's head.
Photograph by James P. Blair, copyright National Geographic Society
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