No creatures like these have ever existed on earth. In laboratories and protected pastures, they produce rare human proteins, mimic human diseases and, in the future, may provide organs for transplant to humans.
These animals cows, sheep, pigs, goats, mice are transgenic. They are created when genes from other species are inserted into egg cells. There, the foreign genes become part of the animal's genome, the set of genetic instructions in every cell. Among other things, these added genes allow transgenic animals to manufacture medically and commercially valuable proteins that can be easily obtained in large quantities from their milk or urine.
Writer Albert Rosenfeld explores this new world with some of the scientists and entrepreneurs who have pioneered it. Such work is both promising and crucial. The American Red Cross, for instance, is counting on transgenic pigs to produce critical supplies of human blood clotting proteins. Besides generating pharmaceuticals, transgenic animals can also provide research models of currently incurable human diseases.
Ralph Brinster, a University of Pennsylvania embryologist and a pioneer of animal transgenics, is sanguine about the future. "When people look back, 50 years from now," he notes, "our ability to modify life-forms will be seen as one of the most important developments in the 20th century."