On the sun-splashed Caribbean island of St. Kitts, Yale University researchers are injecting millions of human brain cells into the heads of monkeys afflicted with Parkinson's disease.
In China, there are 29 goats running around on a farm with human cells coursing through their organs, a result of scientists dropping human blood cells into goat embryos.
The mixing of humans and animals in the name of medicine has been going on for decades. People are walking around with pig valves in their hearts and scientists have routinely injected human cells into lab mice to mimic diseases.
But the research is becoming increasingly exotic as scientists work with the brains of mice, monkeys and other mammals and begin fiddling with the hot-button issue of cloning. Harvard University researchers are attempting to clone human embryonic cells in rabbit eggs.
Such work has triggered protests from social conservatives and others who fear the blurring of species lines, invoking the image of the chimera of Greek mythology, a monstrous mix of lion, goat and serpent.
During his State of the Union speech in January, President Bush called for a ban on "human cloning in all its forms" and "human-animal hybrids," labeling it one of the "most egregious abuses of medical research."
He didn't elaborate, but scientists working in the field believe that by "hybrids," the president meant creating living animals with human traits - something they say they aren't doing.
Other critics are calling for stricter regulations of the research.
"The technology is advancing quicker than the regulations," said Osagie Obasogie of the Oakland-based Center for Genetics and Society, which opposes the mixing of human and animal cells.
But scientists say the ethically charged work will help them better understand disease and hopefully cure some illnesses. They argue their work will never result in the birth of any living being, but lets them experiment with human disease without using people.
"The president touched on a nerve that we all feel," said Doug Melton, the Harvard researcher trying to eliminate the need for women to donate their eggs for cloning research by creating human embryonic stem cells in rabbit eggs.
"The prospect of having animals that are chimeras is frightening. This is not that kind of research. These experiments don't make animals, they make cells."
Melton's work, if successful, would reduce the need for female donors, who have to take fertility drugs to increase their egg production and undergo invasive procedures to extract the eggs. But he has not yet succeeded in extracting human stem cells from the cloned rabbit eggs.
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