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Research Paper #890

Title:Replaying the Tape: an Investigation into the Role of Contingency in Evolution
Authors:Taylor,TJ; Hallam,JC
Date:Mar 1998
Presented:To be presented at the 6th International Conference on Artificial Life, UCLA, June 26-28, 1998
Abstract:The role of contingency (random events) in an artificial evolutionary system is investigated by running the system a number of times under exactly the same conditions except for the seed used to initialize the random number generator at the beginning of each run. Twelve different measures were used to track the course of evolution in each run, and "activity wave diagrams" were also produced (Bedau and Brown 1997). The results of 19 runs are presented and analyzed. The performance of every run was compared with each of the others using a non-parametric test (a randomization version of the pared-sample t test). When comparing absolute values of the measures between the runs some significant differences were found. However, looking at the difference in values between adjacent sample points for a run, no run was significantly different to any other for any of the measures. This suggests that the general behaviour is the same in all runs, but the accumulation of differences results in significantly different outcomes. the results lead us to propose a rule of thumb for future experiments with the system: to check whether the outcome of any particular experiment is robust to contingency in the evolutionary process, at least nine runs should be conducted using different seeds for the random number generator, to be confident of seeing a variety of results. The results are likely to be applicable to other A-Life platforms of self-replicating computer programs, but at this stage can probably tell us little about the role of contingency in biological evolution.

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