The Fitness Landscape
In Avida one can control the selective environment – the topography of the fitness landscape -- in which populations evolve. The metabolic resource required by Avidian critters is computer cycles, and critters – actually lineages of Avidian critters -- can ‘earn’ additional resources by evolving to perform input/output mappings corresponding to various logic functions.
Control of the selective environment is accomplished by editing the environment.cfg file. See the program documentation on your memory stick for details. Note that additional sources of resouces and the way they are earned and consumed can be controlled.