Tierra – Tom Ray’s Artificial World
Tierra was the first example of Silicon-based "life" I discovered. Initially, I read about it in Science News (August 10, 1991). The subject was radical, engrossing, and inspiring. Ray, who has a doctorate in biology, was at the University of Delaware when he created this experiment. Using the sandbox approach in which a computer program acts as a virtual computer environment, Ray simulated life by creating artificial organisms consisting of 32 instructions which served the purpose of genes. Each organism is a small computer program, albeit a program that runs only in the world of the virtual machine. These programs compete with one another, reproduce, and die, much like cellular organisms everywhere. Of course, that’s the idea of creating artificial worlds: to mimic life.
A display consisting of colorful lines provides the view port into this world. The visual tool used is called Almond (Artificial Life Monitor). It was developed for Dr. Ray by Marc Cygnus, a grad student at Delaware. The evolutionary process and competition between organisms is represented by Almond’s shifting rods of color and light. Red rods, for example, show original, 80 instruction set programs. Parasites come on in yellow. They’re of a smaller size – 45 instructions long – and they live off the larger hosts. Blue rods on the display represent parasite-resistant organisms.
The only goal of these artificial creatures is to reproduce themselves. Throughout their lives they execute their instruction set inside the virtual machine. Each series of executions brings the organism closer to death. Two instructions of the set, if executed, rejuvenates the organism so it will live longer. Errors in execution, caused by mutation or misalignment of code, will hasten death. The objective of each organism is to make copies of itself (reproduce) as many times as possible for dying.
Because of mutations, which inserted variety into the gene pool and caused diversity, the original 80 instruction creature was able to spawn the smaller parasites referenced above as well as monster programs as big as 23,000 instructions. These monsters became extinct in the virtual world almost immediately; they just couldn’t keep up with the fast reproducing smaller programs.
Tierra was turned on in January 1990. Today it is a role model for similar endeavors and a standard-setting biosphere that inspires many Alife researchers. Whether or not the creatures in Tierra are really alive is a matter of conjecture, perhaps left to be debated by romantics on one side and doubters on the other. At the very least, Tierra is a window into the world of adaptation and reproduction. The organisms aren’t really organic; they’re life-like. The world they live in is artificial by choice and they can’t change it. They follow rules, just like any other program.