In his 2006 State of the Union speech, President George W. Bush asked the U.S. Congress to prohibit the "most egregious abuses of medical research," such as the "creation of animal-human hybrids." The president's message echoed that of a 2004 report by the President's Council on Bioethics, which recommended that hybrid human-animal embryos be banned by Congress. Discussions of early interspecies research, in which cells or DNA are interchanged...