Choice Relations and Environmental Stability
William M. Baum,
Department of Psychology, University of New Hampshire, USA

According to evolutionary theory, natural selection depends on environmental stability.
If a feature of the environment changes rarely, phenotypic patterns adapted to that feature tend to become fixed in a population. If the environmental feature changes frequently, selection results in simpler responses to the fluctuation. Intermediate levels of change result in intermediate adaptations or compromises between the two possible extremes. If reinforcement resembles natural selection, environmental stability ought to affect behavioral patterns in a parallel way. Results of experiments on concurrent performance at the extremes of environmental stability support this parallel. When reinforcer ratios change rarely, a behavioral pattern including both alternatives ("fix and sample") emerges. When reinforcer ratios change frequently, a simple pattern of reinforcement tracking occurs instead. Intermediate frequencies of changing reinforcer ratios appear to select intermediate performances. These analyses support the parallel between reinforcement and natural selection.

Key words: choice, concurrent schedules, natural selection, reinforcement,
environmental stability

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