They are born. They live their brief life. The fittest of them survive long enough to produce offspring. Over time their descendants evolve, adapting to changes in their environment. Or they fail to adapt and become extinct. They behave, in short, just like living things -- except that they are not flesh and blood but programs that inhabit the memory of a computer.
Can something that "lives" inside a computer really be alive? That is the bizarre question at the heart of artificial-life research, a fast-growing scientific field that seeks to illuminate the nature of life by recreating lifelike behavior in nonliving systems. In laboratories around the world, scientists tapping at computer keyboards are creating electronic versions of biological entities -- proteins, microbes, ants -- that bear a striking resemblance to their living counterparts. In the process, the researchers are raising questions that touch on some of biology's most enduring mysteries: How does nature create order from chaos? How did life emerge from nonlife? What does it mean to be alive?
The most notorious computer life-forms are the electronic viruses that have been injected, inadvertently or maliciously, into computer networks. Like real viruses, these programs are strings of instructional code that have the ability to infect a host computer and reproduce without restraint, sometimes causing considerable damage. But computer viruses are not really alive. They do not evolve or metabolize. And they are created, fully formed, by human programmers. The proponents of artificial life want their life-forms to create themselves, to emerge from nonliving components just as life on earth arose from the primordial ooze.
Nobody claims to have created true artificial life -- yet. But some have come intriguingly close. Christopher Langton, a researcher at New Mexico's Los Alamos National Laboratory, gets credit for coining the term artificial life. $ He was fiddling in the mid-'80s with programs known as cellular automata when he stumbled on a loop-shaped figure that could spontaneously reproduce itself. "That was a watershed," he says. "If you could capture self- reproduction, what else could you do?"
Today hundreds of people are exploring that question. At Bellcore, the research affiliate of the Bell telephone companies, David Ackley makes little creatures with humanoid faces that roam around a computer-simulated world consuming resources, evading predators and multiplying like rabbits. At UCLA David Jefferson and Robert Collins have created colonies of randomly generated "ants" that over many generations evolve the ability to navigate electronic mazes and search for symbols representing food.
Not all artificial life-forms are confined to a computer screen. At M.I.T.'s mobile robot lab (also known as the "artificial insect lab"), Rodney Brooks is building tiny six-legged creatures that are controlled by interconnected computer chips and that display behavior (scurrying for cover, stalking prey) that seems quite purposeful.