A Quantitative Model of the Simpson–Baldwin Effect

G. G. Simpson was the first to explain the Baldwin effect completely in terms of the theory of natural selection. A genetic version of a seemingly non-hereditary adaption may arise when the natural selection acts on the likelihood of having an adaptive trait not just on the trait itself. We present a quantitative model of the Simpson–Baldwin Effect. Organisms in the model have mutable ranges of phenotypic plasticity. The distribution of phenotypes in a population depends largely on the extent of environmental stochasticity. When the environment undergoes intermediate rates of fluctuation, the Simpson–Baldwin effect arises through the interaction of natural selection and mutation on norms of reaction. In a highly volatile environment, organisms benefit from plasticity, and consequently do not experience a Simpson–Baldwin channelling of phenotypic possibility.