Mice are being grown with human brain cells in their brains.Pigs are being raised that have human blood. Sheep withhuman hearts and livers have been created in a Nevadalaboratory. These creatures are called chimeras,human-animal hybrids.

In Europe, China and Japan, even more complex chimeras arebeing created in laboratories that are racing to use thesestrange beings to create radical new treatments that areexpected to revolutionize medicine.

Chimeras make it possible for scientists to study organs asthey function, rather than in artificial laboratorysettings, and represent a tremendous medical advance.

However, there are at present no ethical rules governing thecreation of chimeras, and the National Science Foundation isdeveloping rules now, which it expects to propose in February.

Scientists disagree about these rules. For example, if theonly way to save a human embryo is to implant it into ananimal’s womb, is that ethical, or should it even be legallyrequired if it is the only way to save a baby? And how manyhuman brain cells should be allowed to be implanted in ananimal brain. What if a mouse ends up with a brain made ofall human cells? Would this be unethical or not?

Scientists agree that it is now possible to confer a levelof humanity on animals by implanting them with human braincells. For example, it will soon be possible to increaseanimal intelligence through the use of human brain cells.Such animals might have uses presently undreamed of. Butwould it be ethical?

Even if the US decides that such activies are not ethical,they will be carried out in countries with different values.

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