A couple of weeks ago, the Vatican denounced "experiments [and] genetic manipulation" as "violations of certain fundamental rights of human nature." Bishop Gianfranco Girotti, head of the Apostolic Penitentiary, the Vatican body which oversees confessions and absolutions, told the London Times, "You offend God not only by stealing, blaspheming or coveting your neighbour's wife, but also by ruining the environment, carrying out morally debatable scientific experiments, or allowing genetic manipulations which alter DNA or compromise embryos." So what kinds of genetic manipulation might earn researchers consignment to the flames of Hell should they die unshriven?

First, the Vatican has not spoken with clarity on the issue of genetically improving crops. Back in 2003, the London Times reported that the Vatican would soon come out in favor of biotech crops as part of the solution for world starvation and malnutrition. A year later, a message from Pope John Paul II expressed reservations about biotech crops. Last year, Filipino Archbishop Cardinal Gaudencio Rosales warned that "genetically modified crops and food products could be very harmful to the environment and to human beings." The Archbishop is factually wrong about the alleged dangers of current biotech crops. What are the divine penalties for the sin of scientific ignorance?

The Roman Catholic and generally free market think tank, the Acton Institute, notes that some religious thinkers believe that it might be all right with God for us to modify plants, but not animals. The distinction is based upon the idea that while God commanded Noah to save animal lineages, the Almighty said nothing about preserving plants on the Ark. As evangelical biologist Calvin Dewitt explains, "These lineages are creations of the Creator, and they are... gifts to the whole of creation."

However, the Creator doesn't seem to be much of a steward of His Creation, since an estimated 99.9 percent of all species that ever lived are now extinct. And of course, argument against genetically modifying animals overlooks the fact that the genetic lineages of all domesticated animals have been dramatically modified by people over the millennia. Perhaps the souls of some of our ancestors are roasting in the infernal abyss for the sin of turning wolves into dogs and aurochs into Holsteins.

Of course, modern scientists are constantly tampering with the genetic make-up of animals. Just this week, researchers at Memorial Sloan Kettering Cancer Center in New York announced that they had used embryonic stem cells to cure Parkinson's disease in mice. The researchers, using a technique called nuclear transfer, isolated the nuclei from skin cells from the tails of mice that suffered from Parkinson's disease and installed them in mouse eggs that had been stripped of their nuclei. These eggs started growing into embryos that were genetic clones of the mice from which the skin cells were taken. The researchers then derived stem cells that were genetically matched to each individual mouse and in turn transformed the stem cells into dopamine producing neurons. These genetically matched neurons were injected into the brains of the mice.

The treatment worked. These perfect genetic cellular transplants basically cured the mice. As a control the researchers treated other mice with neurons derived from embryonic stem cells that were not genetically matched to each individual mouse. Those mice fared worse. This work is aimed at figuring out eventual treatments for the 1.5 million Americans who suffer from Parkinson's disease. Can research on mice designed to heal sick people really count as sinful genetic manipulation?

Also this week religious controversy broke out in Britain over new legislation that would allow researchers to combine abundant eggs from animals like cows and rabbits with human nuclei as way to produce stem cells. The BBC reported that Cardinal Keith O'Brien used his Easter sermon to condemn the bill as a "monstrous attack on human rights, human dignity and human life." In contrast, some 200 British medical charities signed a letter urging Parliament to pass the legislation. "The bill will allow new avenues of scientific inquiry to be pursued which could greatly increase our understanding of serious medical conditions affecting millions of people throughout the UK," declared the charities.

Roman Catholic bioethicist Michael Cook, who also opposes the combining human and animal genes, asserts, "To envelop all that makes us human, our genetic inheritance, in an animal carapace is creepy and repugnant." I wonder how "creepy and repugnant" Cook would find the fact that out of the 23,000 genes that comprise the human genome as few as 50 to 100 genes do not have counterparts in other animals. Our genetic make-up has come down to us through the animal carapaces of our evolutionary forebears. Of course, while our genes are very similar to animal genes, it is differential regulation of those genes that accounts for much of what makes us distinctively human.

O'Brien and Cook clearly believe that in some sense the human genome is sacrosanct. But surely it is morally laudable to insert the human insulin gene into bacteria to produce a better medicine for 14 million diabetic Americans. Or what about cows with human genes to produce human antibodies to fight disease? Human skin color genes in fish? Human color vision genes in mice? I suspect that Cardinal O'Brien and Cook do not think such manipulations of single human genes are monstrous or creepy. It is true that the proposed human animal cybrids would contain mostly human genes, but researchers have no intention of creating cow/human or rabbit/human babies. So perhaps it is the quantity of human genes involved in experiments that provoke accusations of monstrous violations of human dignity. That doesn't seem to be the case.

For example, a number of prominent Roman Catholic thinkers recently endorsed a proposal by Stanford University bioethicist William Hurlbut to create human stem cells through altered nuclear transfer. The technique is essentially the same as regular nuclear transfer except that it uses RNA interference to disable a single crucial gene so that the stem cells cannot grow into a fully developed embryo. In altered nuclear transfer all of the genes involved are human, even the one that has been deliberately broken. But doesn't altered nuclear transfer circle us back to Bishop Girotti's denunciations? The technique could be interpreted as "genetic manipulations which alter DNA or compromise embryos."

Finally, any genetic manipulations that aim to create human beings with diminished mental and physical capacities must be fiercely and relentlessly opposed. On the other hand, research whose goal is to reduce human suffering and increase our capacities should be vigorously encouraged.

In tracing these theologico-biotech controversies, many contemporary thinkers and leaders in the Roman Catholic Church appear to be haunted by the fear that scientific research will transgress God's will. It's as though they still find some wisdom in the old adage, "If God had meant for people to fly, He would have given them wings." But it could also be the case that "if God hadn't meant for people to fly, then He wouldn't have given them the brains to figure out how to do it." Finally, if the Vatican is looking for new sins, perhaps it would consider adding attempts to block important scientific research to the list.

Ronald Bailey is reason's science correspondent. His most recent book, Liberation Biology: The Scientific and Moral Case for the Biotech Revolution, is available from Prometheus Books.