Energy is the single currency by which agents survive, reproduce, and die, and it must be positively correlated with some performance measure for the task defined by the environment. Agents asynchronously go through a simple cycle in which they receive input from the environment as well as internal state, perform some computation, and execute actions. Actions have an energy cost but may result in energy intake. Agents that perform the task better than average reproduce more and colonize the population. Indirect interaction among agents occurs without the need of expensive communication, via competition for the shared, finite environmental resources.
Mutations afford the changes necessary for the evolution of dynamically adapted agents.
Associating high energy costs with expensive actions intrinsically limits the computational load. In the heterogeneous environment of the WWW, it is hard to associate a fitness measure with a strategy in general, but it is easy to estimate the results of a strategy applied to a particular query. Different information search and retrieval strategies may be optimal for different queries, just as different behaviors may be optimal for different environments. Therefore populations will quickly evolve strategies effective in the different environments specified by both information space and queries. Adaptation means for agents to concentrate in high energy areas of the Web, where many documents are relevant.