Until about a decade ago, there was only one way to make an embryo—the old-fashioned technique of combining an egg with a sperm. Then came Dolly the cloned sheep in 1996. Scottish scientists created her by injecting the nucleus of a breast cell from one sheep into the enucleated egg of another sheep. Dolly was essentially genetically identical to the donor of the breast cell nucleus.
Since then researchers have used reproductive cloning to produce mice, cats, dogs, horses, cows, goats, pigs, and other mammals. As valuable as reproductive cloning is for producing livestock and research animals, most researchers were excited by the prospect of using cloning to create human embryonic stem cells. These stem cells produced by therapeutic cloning might be used to grow perfect transplants to replace and repair damaged tissues and organs.
Therapeutic cloning to produce transplants fell directly into the heated abortion debate. From the pro-life point of view, cloned human embryos, like all other embryos, have the same moral status as adult human beings. The moral status of five-day embryos is still contested. Hoping to avoid controversy, researchers searched for sources of cells that would have the valuable properties of embryonic stem cells (self-renewing and transformable into any type of cell), but would be acceptable to pro-lifers.
One proposal is to create human stem cells using altered nuclear transfer (ANT). Championed by Stanford University bioethicist William Hurlbut, the technique is essentially the same as regular cloning except that it uses RNA interference to disable a single crucial gene so that the cloned entity cannot implant into a womb and thus cannot grow into a fully developed embryo. In ANT all of the genes involved would be human, even the one that has been deliberately broken.
A number of prominent Roman Catholic thinkers recently endorsed ANT as a morally acceptable way to produce human embryonic stem cells. So whether or not an entity can house a human soul evidently depends on the timing of the operation of a single gene. Other theologians question this, asking why such a cloned entity should not be considered a defective human embryo deserving of same the moral solicitude owed to disabled adult human beings.
The search for a morally unproblematic source of stem cells continued. Last fall, Shinya Yamanaka and his colleagues at Kyoto University in Japan and another team at the University of Wisconsin announced the good news that they had been able to transform adult human skin cells into cells that act very much like embryonic stem cells. Yamanaka took skin cells and inserted four genes—Oct4, Sox2, Klf4 and Myc—that are expressed in embryonic stem cells, causing the skin cells to revert to the embryonic state. These induced pluripotent stem (iPS) cells are generating a huge amount of excitement among stem researchers and were even hailed as the end of the stem cell wars.
Well, not quite. The Kyoto and Wisconsin researchers used skin cells originally derived from human fetuses in their research. Still, such cells are not necessary to generate new iPS cells; they were just convenient. But let's approach the moral issue from another direction.
It turns out that, at least in mice, injecting iPS cells into mouse blastocysts creates chimeric mice. The iPS cells are incorporated into the developing mouse embryo and form part of the tissues and organs of new mouse pups. Researchers at the Whitehead Institute in Massachusetts have gone even further. They created a mouse comprised entirely of iPS cells. The iPS cells form an embryo after they are embedded into tetraploid embryonic cells that grow into a placenta. There is no apparent reason why this technique wouldn't work in humans.
In April, this insight caused The Independent to hyperventilate, "Now we have the technology that can make a cloned child." The Independent quotes stem cell researchers Robert Lanza: "It raises the same issues as reproductive cloning and although the technology for reproductive cloning in humans doesn't exist, with this breakthrough we now have a working technology whereby anyone, young or old, fertile or infertile, straight or gay can pass on their genes to a child by using just a few skin cells." Maybe so, but iPS cell research raises an even more intriguing question.
Back in 1999, during a hearing of the National Bioethics Advisory Commission, then-Director of the National Institutes of Health Harold Varmus made the intriguing observation that "It may eventually become possible to take a cell from any one of our organs and to expose it to the right set of environmental stimuli and to encourage that cell to return to a more primitive stage in the hierarchy of stem cells. Under those conditions, one might in fact generate the cell with as great a potential as a pluripotent cell from a very mature cell." Nine years later Yamanaka proved that Varmus was prophetic.
Varmus continued, "One might even in fact imagine generating a cell that is totipotent [able to develop into a complete organism] in that manner." In other words, researchers may one day take human cells all the way back to the embryonic stage, at which point they could be implanted into a womb, where they could eventually develop into complete human beings. This is the direction in which iPS cell research is heading. So instead of switching off one gene to make sure that an entity is not worthy of their moral concern, pro-lifers may soon have to worry about the opposite, pushing an adult cell so far back in its developmental stage that switching on a single gene will turn it into an embryo.
Advances in stem cell research may be provoking a kind of "God of the Gaps" retreat on the moral status of embryos. People who subscribe to God of the Gaps thinking believe that the hand of God can be seen in those things which science cannot explain. In this case, the closing gaps in the details of molecular biology are forcing pro-lifers into an uncomfortable corner where they have to decide whether or not a cell can be imbued with a soul by turning a single gene on or off.
Ronald Bailey is reason's science correspondent. His book Liberation Biology: The Scientific and Moral Case for the Biotech Revolution is now available from Prometheus Books.