Strategies and Rubrics for Teaching Chaos and Complex Systems Theories as Elaborating, Self-Organizing, and Fractionating Evolutionary Systems Fichter, Lynn S., Pyle, E.J., and Whitmeyer, S.J., 2010, Journal of Geoscience Education (in press)

Avida and Tierra

Tierra represents an entirely new class of genetic algorithms. The Tierran ecosystem consists of hand crafted organisms, but ones capable of self-replication and open-ended evolution independent of the designer. Once the initial replicator (the ancestor) is created it is capable of self-evolving its own code to enhance its own survival. In other words, what is evolving here is the computer’s code, the instructions usually written by the programmer.

Although the model is limited to the evolution of creatures based on sequences of machine instructions, this may have a potential comparable to evolution based on sequences of organic molecules. Sets of machine instructions similar to those used in the Tierra Simulator have been shown to be capable of “universal computation” and in this sense are like a Universal Computer.

This system results in the production of synthetic organisms based on a computer metaphor of organic life in which CPU time is the “energy”' resource and memory is the “material” resource. Memory is organized into informational patterns that exploit CPU time for self-replication. Mutation generates new forms, and evolution proceeds by natural selection as different genotypes compete for CPU time and memory space.

The Digital Environment: Self-replicating computer programs (colored geometric objects) occupy the RAM memory of the computer (orange background). Mutations (lightning) cause random changes in the code. Death (the skull) eliminates old or defective programs.

The Ancestral Program - consists of three ``genes'' (green solid objects). The CPU (green sphere) is executing code in the first gene, which causes the program to measure itself.

The Digital Environment: Self-replicating computer programs (colored geometric objects) occupy the RAM memory of the computer (orange background). Mutations (lightning) cause random changes in the code. Death (the skull) eliminates old or defective programs.

Evolutionary History in Tierra

Hosts, red, are very common. Parasites, yellow, have appeared but are still rare.

Hosts (red), are now rare because parasites (yellow) have become very common. Immune hosts, blue, have appeared but are rare.

Immune hosts (blue) are increasing in frequency, separating the parasites into the top of memory.

Immune hosts (blue) now dominate memory, while parasites (yellow) and susceptible hosts decline in frequency. The parasites will soon be driven to extinction.

A Parasite (blue, two piece object) uses its CPU (blue sphere) to execute the code in the third gene of a neighboring host organism (green) to replicate itself, producing daughter parasite (two-piece wire frame object). A Hyper-parasite (red, three piece object) steals the CPU from a parasite (blue sphere). Using the stolen CPU, and its own CPU (red sphere) it is able to produce two daughters (wire frame objects on left and right) simultaneously.