The National Academies of Science has issued a set of guidelines for human embryonic stem (ES) cell research. The guidelines also address the chimera phenomenon.

The guidelines open a path for experiments that create animals that contain some introduced human embyronic stem cells.

These hybrid part human, part animal creatures, called chimeras, would be “valuable in understanding the etiology and progression of human disease and in testing new drugs, and will be necessary in preclinical testing of human embryonic stem cells and their derivatives,” the mittee said.

Chimeras might also be used to grow organs, such as livers, to transplant into humans.

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Human embryonic stem cells should be introduced into nonhuman mammals “only under circumstances where no other experiment can provide the information needed,” the guidelines say.

The danger is experiments in which there is a possibility that human cells could contribute in a “major organized way” to the brain of an animal. These experiments “require strong scientific justification,” mittee warned.

Once again we can see that the overriding ethical principle is a scientific pragmatism. Almost no limit is viewed as absolutely impassable, as long as “no other experiment can provide the information needed.”