Dr. David Stevens, executive director of the Christian Medical and Dental Associations, based in Bristol, Tenn., believes that the creation of chimeras is all right as long as it does not utilize human embryonic stem cells,  which he sees as morally wrong, and does not "get to the point of changing the nature of the animal or the human being." 

By this definition, using human adult cells to make pig or sheep organs more viable for transplant to a human recipient -- without changing that animal's natural behavior or appearance -- would be acceptable. But to modify an animal so that it would bear any resemblance to a human would not only "create a ‘yuck' factor," according to Stevens, it would also violate the moral and ethical teachings of The Bible, which dictate that human beings "have stewardship" over animals, and it could even "alter the essence" of a human being.

The role of God and moral values in science is certainly an area of great debate lately -- as witnessed by the current evolution hearings in Kansas, debating how to teach the ideas of evolution versus intelligent design to public school students. Balancing the need for scientific freedom and the pressure to impose tighter ethical restrictions means that these recent guidelines may well be just the first step in a long road to reaching a chimerical compromise. 

Dr. Richard Hynes, MIT's Daniel K. Ludwig Professor for Cancer Research, and one of the co-chairs of the committee that helped put together the NAS report, says it's "likely these guidelines will need to be tuned…it just isn't possible to anticipate what might come up."

But he believes that putting a basic framework out there will "allay the controversy somewhat…we don't want people to think of this as just [making] monsters.