In Echo, an agent replicates when it has acquired enough resources to copy its genome. The local state of an agent is exactly the amount of these resources it has stored and its location in the world.
Agents acquire resources through interactions with other agents (combat or trade) or from the environment. Echo specifies certain structural features of the environment in which agents evolve.
In a 2-D grid, "sites", there are many agents at one site. Each site produces renewable resources. Resources are represented by different letters of the alphabet, and genomes are constructed from the same letters.
There are three forms of interactions: trade, combat and mating. In trade, resources stored in the reservoir are exchanged; in combat, all resources are transferred from loser to winner; in mating, genetic material is exchanged through crossover. Mating, together with mutation during the replication process, provides the mechanism for new types of agents to evolve.
Resource constraint provide the selective pressure for agents to develop alternative strategies for survival and reproduction.
Case study: Echo resemble nature? (on species diversity)