Embryonic stem cells, with their unique power to differentiate into every type of cell in the human body, have been hailed as the source of possible cures for everything from heart disease to Parkinson's but reviled by antiabortion activists, who oppose harvesting the cells from surplus frozen embryos. When the U.S. government decided in 2001 to deny funding for research that uses embryonic cells derived after August 9, 2001, observers predicted a brain drain of U.S. researchers to Europe.

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