Science 285 p. 1663
Random Samples 10 September 1999 Evolving Toy Story Few people over the age of 9 would think of Lego construction toys as the building blocks of life. But now two Brandeis University scientists have shown that with a computer program based on evolutionary principles it is possible to "breed" a structure, such as a bridge or a crane. It's a step, they say, toward the "evolutionary" design of robots. Computer scientist Jordan Pollack and graduate student Pablo Funes designed their structures on a computer using a "genetic algorithm" based on 1000 randomly chosen brick designs. The patterns may evolve in two ways: "Mutation," which will randomly add or change the position of a brick, and "Crossover," which will randomly switch components of two "parent" designs. Each design got a "fitness" score based on weight-bearing ability (for the cranes) or length of span (for the bridges), which determined how likely it would be to have "offspring." When a promising structure eventually evolved, Pollack and Funes would build one out of Lego bricks and test it. The resulting structures are clumsy and inefficient-looking, but they perform as their simulations promise. They demonstrate, says Pollack, that "an incredibly stupid and simple algorithm" can spur the evolution of unprogrammed features. The cranes, for example, evolved a basic engineering principle, always adding vertical struts to add strength to a diagonal arm. "The unique thing" about Pollack's work, says robotics researcher Randall Beer of Case Western Reserve University in Cleveland, is that he hasn't stopped with computer simulations but is "actually building and testing the evolved structures."