A mix of mice and men
Injecting animals with human genes raises huge ethical questions - not to mention the 'yuck factor.'
In Greek mythology, they were monsters - with the head of a lion, the body of a goat, and the tail of a serpent. But today's chimeras (pronounced ky-MIR-uhs) are being crafted for a far different purpose. Scientists hope that by mixing genes of different animals they can better understand human biology and eventually test new drugs more safely and accurately, harvest organs for transplant into humans, and find new cures for human diseases.Skip to next paragraph
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There's just one twist: the genes being mixed are animal and human. Already in Israel, researchers have put human embryonic stem cells into chick embryos. In Switzerland, they've created mice with human immune systems; in Minnesota, pigs with humanlike blood; in Nevada, sheep with near-human livers.
Many people find the whole idea morally repugnant, even if they have a hard time articulating just why this "yuck factor" bothers them. Bioethicists and others are also struggling to reason their way through the issue, weighing possible benefits and risks. The President's Council on Bioethics is studying human-animal chimeras. Next month, the National Academies of Sciences will release guidelines on whether they're ethical to make. Congressional aides are investigating them, too, with thoughts of drafting legislation.
Inevitably, ethicists are led to debate several questions. Just what makes humans unique? When would a chimera become too human? And, if it did show human physical or behavioral traits, why would that be wrong?
After all, pig heart valves have been used to replace human ones for years. But experiments involving brains, which seem to come much closer to affecting the identity of a man or beast, bring deeper discomfort and more troubling discussions.
Irving Weissman, a researcher at Stanford University, for example, has proposed creating mice with brains containing 100 percent human neurons. By studying such mice, researchers might find cures for diseases such as Parkinson's and Alzheimer's, he reasons.
"Scientists are under a lot of pressure to be creative," adds Jason Robert, a bioethicist at Arizona State University in Tempe, "to come up with solutions that will help lessen the lag time between basic research and [medical cures]. But it's not clear that building chimeras is going to solve the problem."
Another complicating factor: The research involves the use of human stem cells, already a hot-button issue. "We've focused so much on the moral status of the [human] embryo that we've forgotten that there are other [ethical] issues coming to the fore," says Cynthia Cohen, a senior research fellow at the Kennedy Institute of Ethics at Georgetown University in Washington and an adviser to the Canadian government on stem-cell research.
"What we're really worried about is creating some sort of creature that would be functioning like a human being and yet having very strong animal-like features," Dr. Cohen says.
What, then, makes humans distinctive? Cohen argues that there are "a cluster of characteristics" either that are unique to humans or that humans express to a greater degree than animals, including the ability to distinguish right from wrong, make decisions and act on them, do complex thinking, and develop empathy. To keep these qualities distinct in humans preserves human dignity, she says.
But the proposed Stanford experiment would have had little likelihood of producing mice with any human behavioral characteristics, says Henry Greely, a professor of law at Stanford and the chairman of an ad hoc university committee that two years ago informally advised Weissman on the ethical implications of his venture. "Certainly if the mouse stood on its hind legs and said, 'Hi, I'm Mickey!' we'd be worried," says Professor Greely, who is also director of the Stanford Center for Law and the Biosciences. "We'd be more than worried."