In the late 1950s, soon after Watson and Crick had discovered DNA's structure, scientists began predicting that someday we'd be able to genetically engineer our children. We'd design them to be healthy, smart and attractive, with life spans of 200 years, photographic memories, enhanced lung capacity for athletic endurance, and more. Our children would pass these modifications to their own children and add new ones as well. Humanity would take control of its own evolution and kick it into overdrive.

Few people took these speculations very seriously. Could this sort of genetic engineering really be done? Even if it could, would anyone really want to do it? If they did, wouldn't society step in and set limits? In any event, wouldn't it be decades before we'd have to worry about this?

Now it's 2004, and those decades have passed. The era of genetically modified humans is close upon us. Almost every day we read of new breakthroughs: cloning, artificial chromosomes and now high-tech sex selection. Scientists create genetically modified animals on an assembly-line basis. Biotech entrepreneurs discuss the potential market...