IAN WILMUT IS famous now as the man who cloned an adult mammal for the first time. But Wilmut did not actually set out to be the first to clone an adult mammal; he was working on cloning as a means to an end, not as an end in itself. Wilmut and his colleagues at PPL Laboratories in Roslin, Scotland, had originally intended to develop new treatments for genetic disorders in human beings. Among the disorders they were most interested in is the blood disease called hemophilia.

Hemophilia: a genetic disorder

Although the drugs that people take to treat and cure their illnesses are usually produced in laboratories, the basic ingredients of those drugs often come from nature. Penicillin is derived from a mold, for example, and aspirin comes from willow bark. Some diseases, such as hemophilia, are caused by the body's...