“It is hard to imagine what human life will be like even a hundred years from now, but I suspect that the reworking of our own biology will figure heavily in our future.” —Gregory Stock, director of the Program on Medicine, Technology, and Society at the University of California, Los Angeles, School of Public Health

In the early 1970s scientists developed the fundamental techniques of recombinant DNA technology—the artificial addition, deletion, or rearrangement of genetic sequences in order to alter the form and function of an organism. The resulting technologies, known as genetic engineering (GE), include gene therapy, which aims to replace defective genes with healthy genes; gene splicing, which involves the genetic modification of crops by inserting the genetic material of a natural insecticide or vitamins; and cloning, the production of identical genetic copies, which is often used to create the genetic...