Constraints on Phenotypic Evolution

Constraints on phenotypic evolution can take a variety of forms. Constraints can arise from inheritance, selection, development, and design limits. Contemporary visions of the evolutionary process often focus on one or two of these varieties and ignore the others. A unifying framework that considers all four major varieties of constraint is emerging within the discipline of quantitative genetics. I attempt to sketch that emerging framework and summarize recent efforts toward unification. Although couched in the technical language of quantitative genetics, the ongoing search for a common framework promises a rapprochement among the approaches of optimality theorists, population geneticists, and developmental biologists.