Greek legend tells of a fire-breathing monster called a chimera. This fearsome patchwork beast-part dragon, part goat, and part lion-terrorized the countryside until a hero destroyed it.

In the mid-1970s many people were equally terrified to find out that scientists had begun making chimeras of their own. These new creatures, containing genes from different kinds of living things, were so small that they could be seen only with a microscope. Still, popular thinking-and the thinking of some scientists as well-held that they might turn out to be monsters all the same. A few people, however, hoped they would prove to be angels in disguise.

Gene Splicers

California scientists led the way in developing what came to be called gene-splicing, recombinant DNA technology, or genetic engineering: artificially combining genes from different species of living things. Paul Berg of Stanford University...