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The winner collects the loser's resources, both the resources in its reservoir and the resources tied up in its chromosomes (broken into individual letters). In some models, the winner collects only some of the resources of the loser, the rest being dissipated. The provision of separate offense and defense capabilities, with possible asymmetries, allows the system to evolve intransitive relations between agents wherein, for example, X can ''eat" Y, and Y can "eat" Z, but X cannot "eat" Z. As a consequence, various kinds of "food webs" can evolve. |
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2. Trading. If combat does not take place, then the first agent in the pair checks its trading condition against the offense tag of the second agent, and vice versa. Unlike combat, which can be initiated unilaterally, trading is bilaterala trade does not take place unless the trading conditions of both agents are satisfied. The trading condition in the simplest model has a single letter, as a suffix, that specifies the resource being offered for trade. If the trade is executed, then each agent transfers any excess of the offered resource (amounts over and above the requirements for its own reproduction) from its reservoir to the reservoir of its trading partner. Though this is a very simple rule, with no bidding between agents, it does lead to intricate, rational trading interactions as the system evolves: Trades that provide resources needed for reproduction increase the reproduction rate, assuring that agents with such rational trading conditions become common components of the population. |
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3. Mating. While an agent can reproduce asexually, simply making a copy of each of its chromosomes when it has accumulated enough resources (letters), there is also a provision for recombination of chromosomes. When agents come into contact and do not engage in combat, the mating condition of each agent is checked against the mating tag of the other. As with trade, mating is only executed as a bilateral action: Both agents must have their mating conditions satisfied for recombination to take place. If this happens, then the agents exchange some of their chromosome material, as with crossover under the genetic algorithm. (The procedure is reminiscent of conjugation between different mating types of paramecia). This selective recombination provides a powerful mechanism for discovering and exploiting useful schemata. The effect is very like the effect that the schema theorem(s) of chapter 7 project, though the schema theorems cannot be applied directly to Echo's agents because they have no explict fitness function. |
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In addition to these three agent-agent interactions, there is one direct interaction with the environment. The geography of Echo consists of a set of sites, laid out in some |
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