http://chronicle.com/daily/2003/05/2003050802t.htm
Researchers are reporting today that they have used computer simulations to prove an important aspect of evolutionary theory: that complex structures, like an eyeball, can arise through evolution.
The researchers showed that so-called digital organisms -- computer programs that can mutate, reproduce, and compete with one another -- can evolve highly complicated logical formulas within their programs. Such formulas, the researchers say, are analogous to complicated organs like eyeballs in an actual creature.
In an argument known as "intelligent design," critics of evolutionary theory maintain that such organs could not have arisen through gradual evolution of their components and must have been produced through the intervention of an intelligent force, such as God.
However, the researchers who performed the simulation, reported in today's edition of Nature, say that their results show that complicated organs need not be consciously fashioned by an intelligent agent.
The researchers, from the California Institute of Technology and Michigan State University, started with 3,600 identical copies of a computer program. The program contained a set of 15 instructions on how to make a copy of itself and 35 copies of another instruction that performed no function.
Then, the programs were allowed to reproduce. Like biological reproduction, the simulation's process of reproducing programs was imperfect, producing spontaneous errors in the copied versions of the programs, akin to mutations in DNA. Although many of the mutations harmed the digital organism or had no effect on it, certain combinations of mutations enabled the program to perform specific logical functions.
Under the rules of the simulation, programs that were able to execute complex logical functions were rewarded with more energy and therefore were able to reproduce more frequently than programs that were unable to perform the functions. The greater the complexity of the logical function performed, the greater the energy reward.
The experiment was run simultaneously on 60 computers working cooperatively in an arrangement called a Beowulf cluster. After more than 15,000 generations, the researchers found, the population of computer programs included many that contained complex programming. For example, some of the programs had the ability to compare two values, each of which was 0 or 1, and determine if the two values were equal. Although this function may sound simple, it depended on the program's executing 35 specific instructions.
But Michael J. Behe, a professor of biological sciences at Lehigh University who is one of the most vocal proponents of intelligent design, says that the simulation proves nothing. "If I were a Darwinist, I would be embarrassed for this paper to be published in Nature," he said.
"There's precious little real biology in this project," Mr. Behe said. For example, he said, the results might be more persuasive if the simulations had operated on genetic sequences rather than fictitious computer programs.
But Richard E. Lenski, a professor of microbial ecology at Michigan State who is one of the project's researchers, said that the simulations captured three of the most basic attributes of life forms: replicating, mutating, and competing with others. Consequently, the behavior of the digital organisms can shed light on the evolution of actual life forms, he said.
For example, the simulations showed that some mutations that initially were harmful turned out in later generations to have been fortuitous because they served as the basis for further, beneficial mutations that produced logic functions, Mr. Lenski said.
Biologists acknowledge the theoretical possibility of such "unexpected twists" in the evolutionary process, but in practice they nevertheless often conceive of evolution as a solely "uphill" process of continual improvement in an organism, he said. The evolutionary paths of the simulated creatures could help researchers embrace a more-complex view of evolution that incorporates both backward and forward steps, he said.