5.17: Cloning—ranging from genes to organs to individuals—offers both promise and perils.

Cloning. Perhaps no scientific word more readily conjures horrifying images of the intersection of curiosity and scientific achievement. But is fear the appropriate emotion to feel about this burgeoning technology? Perhaps not.

For starters, let’s clarify what the word means. “Cloning” actually refers to a variety of different techniques. To be sure, cloning can refer to the creation of new individuals that have exactly the same genome as the donor individual—a process called “whole organism cloning.” That is, a clone is like an identical twin, except that it may differ in age by years or even decades. It is also possible to clone tissues (such as skin) and entire organs from an individual’s cells. And, as we saw in Section 5-12, it is possible to clone genes.

Cloning took center stage in the public imagination in 1997, when Ian Wilmut, a British scientist, and his colleagues first reported that during the previous year they had cloned a sheep—which they named Dolly. Their research was based on ideas that went back to 1938, when Hans Spemann first proposed the experiment of removing the nucleus from an unfertilized egg and replacing it with the nucleus from the cell of a different individual. Although the process used by Wilmut and his research group was difficult and inefficient, it was surprisingly simple in concept (FIGURE 5-42). They removed a cell from the mammary gland of a grown sheep, put its nucleus into another sheep’s egg from which the nucleus had been removed, induced the egg to divide as if it were a naturally fertilized egg, and transplanted it into the uterus of a surrogate mother sheep. Out of 272 tries, they achieved just one success. But that was enough to show that the cloning of an adult animal was possible.

Shortly after news of Dolly’s birth, teams set about cloning a variety of other species, including mice, cows, pigs, and cats (FIGURE 5-43). Not all of this work was driven by simple curiosity. For farmers, cloning could have real value. It can take a long time to produce animals with desirable traits from an agricultural perspective—such as increased milk production in cows. And with each successive generation of breeding, it can be difficult to maintain these traits in the population. But with transgenic techniques and whole animal cloning, large numbers of valuable animals with such traits can be produced and maintained.

Medical researchers, too, see much to gain from cloning. In particular, transgenic animals containing human genes—such as the hamsters producing rhu-EPO, discussed earlier—can be very valuable. But can a human be cloned? At this point, it is almost certain that the cloning of a human will be possible. Many people wonder, though, whether such an endeavor should be pursued. There is near unanimity among scientists that human cloning to produce children should not be attempted. Some of the reasons cited relate to problems of safety for the mother and the child, legal and philosophical issues relating to the inability of cloned individuals to give consent, problems of the exploitation of women, and concerns regarding identity and individuality. Governments are struggling to develop wise regulations for this new world.