Leonard Adleman sends his regrets. In an e-mail FAQ he uses to fend off journalists seeking interviews, the University of Southern California computer scientist and world-famous cryptographer who invented the field of DNA computing confesses that "DNA computers are unlikely to become stand-alone competitors for electronic computers." He continues, somewhat apologetically: "We simply cannot, at this time, control molecules with the deftness that electrical engineers and physicists control electrons."

It was in 1994 that Adleman first used DNA, the molecule that our genes are made of, to solve a simple version of the "traveling salesman" problem. In this classic conundrum, the task is to find the most efficient path through several cities-given enough cities, the problem can challenge even a supercomputer. Adleman demonstrated that the billions of molecules in a drop of DNA contained raw computational power that might-just might-overwhelm silicon. But since then, scientists have run into tough practical and theoretical barriers. As Adleman and others in the field have come to realize, there may never be a computer made from DNA that directly rivals today's silicon-based microelectronics.