The occurrences occur in distinct patterns - connected sequences which rise chaotically to a peak over several weeks but which then peters out. Futhermore it not generated by only one (or a a few) agents, but a substantial proportion of the agents participate, one after the other. The distribution of who says "IPredictedLastWeek", when is shown below in figure 8 (Agent-3 has not been included since it never utters this particular message part).
Figure 8. The distribution of utterances of "IPredictedLastWeek" by agent
If one kept one's analysis at the level of the emergent communication it would appear that an utterance is started by one agent which is then spread by the rest of the population until it losses the ability to impart comparative advantage on its speakers and so is selected out. This sort of emergent pattern of communication occurred with a variety of different messages at different stages in the simulation. Add to these observations the knowledge that are mechanisms built into the agents that would allow the selective propagation of utterances from agent to agent, so that strategies that supported a memetic process between agents could evolve and one might feel quite safe in concluding it is a memetic process.
However, if one analyses the actual strategies that the agents used, then one gets a different picture. The similar utterances that were observed were not generally a result of imitative strategies learned by the agents (as in figure 5). In figure 9, I exhibit a similar graph to that of figure 7, but separated into those utterances of "IPredictedLastWeek" that were as a result of imitation by an agent and those that are the result of other mechanisms. I compiled this by analysing the actual strategies for communication learned by the agents at each date where these utterances occurred to see how they were derived. These other utterances arose because they were simultaneously determined as relevant by the learning of each agent. What memetic imitation there was is attributable to chance copying - a sort of weak `echo' of other utterances. These utterances with `IPredictedLastWeek' in them were not selected for by these agents. In particular one does not find any branching chains supporting the presence of memetic copying of messages. In fact there is only one instance of such a message being passed down the generations for more than one notional week (this occurs in the middle of the simulation, barGoer-3 at week 16 is copied by barGoer-2 at week 17 which is copied by barGoer-7 at week 18 and then by barGoer-8 at week 19), and even then there is no replication of the meme into more than one strand.
Figure 9. Number of occurrences of "IPredictedLastWeek" in agent utterances analysed by generating process
The fact that the learning processes in this simulation are achieved via an evolutionary mechanisms is beside the point. It does not make the process of messages between agents into a memetic one. A memetic process could have co-evolved if the agents evolved models to do so, but this did not happen here. The agents did sometimes copy from each other but not so as these copying processes where chained into a memetic process so that we could meaningfully say the messages themselves underwent an evolutionary process.
If this sort of pseudo-memetic process can occur in an artificial simulation where mechanisms are explicitly built in a mechanism for the expression, propagation and selection of memes by agents, then it is possible that similar processes could be happening elsewhere. Thus it is wrong to imply the existence of memetic process, purely as a result of a post-hoc analysis of data and the mere presence of possible mechanisms. Such `black-box' models are insufficient on their own.
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On Modelling in Memetics - Bruce Edmonds - 18 AUG 98
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