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.
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