The Role of Chance^6.3

  Some of the results reported in the previous chapter suggest that chance events may have played a significant role in the outcome of the run (see Section 5.2.7). As discussed in Section 2.3.5, it is generally accepted that contingency (``historical accident'') has played a large part in determining the course of evolution on Earth, although there is still much debate as to the relative importance of chance events versus other factors (e.g. the inherent self-organisational properties of the biochemical world, discussed in Section 2.1.1). With artificial evolutionary systems we have the advantage of being able to ``replay'' evolution under experimental control. When considering the performance of an evolutionary system, we generally wish to disentangle the relative influence of three factors: (1) contingency, (2) performance due to particular details of the system's design, and (3) performance which may be general to a wide class of evolutionary systems [Taylor & Hallam 97]. In this section, an experiment is reported in which Cosmos was run a number of times, varying just the random number seed between runs. The results will give us a better idea of the role of contingency in the system.