   One issue in the debate over adaptationism and optimality models concerns whether constraint hypotheses count as genuine alternatives to adaptive hypotheses. Gould and Lewontin (1979) view constraint hypotheses as competing with adaptive hypotheses as explanations of traits. Advocates of optimality models (e.g., Maynard Smith 1978, Roughgarden 1998) take the set of evolutionary constraints to be a background commitment of any optimality model. The constraint set may include developmental and genetic constraints on variation and transmission, but it is natural selection that drives evolution and so explains the trait given those constraints. Advocates of optimality models treat constraints as presupposed by adaptive hypotheses. A concern of many critics of adaptationism is that this treatment of constraints undervalues their role in explaining evolutionary form and novelty.