   Orzack and Sober provided a specific protocol to assess whether O is true for a particular trait. It involves comparing the predictive accuracy of a “censored” evolutionary model, one that invokes only natural selection, and an alternative “uncensored” model that invokes additional evolutionary influences such as genetic drift (random trait change caused by population number being finite), or constraints caused by the way the trait is determined genetically or developmentally. If the censored model is quantitatively accurate and there is no within-population heterogeneity of fit to predictions and the uncensored model fails in either regard, then one can infer that natural selection is a sufficient explanation for trait T. Optimality models embody proposition (O) in that natural selection is assumed to be the only important influence on the focal trait's evolution; the result is assumed to be the evolution of a trait that maximizes individual fitness. Of course, an optimality model, like any evolutionary model, must include background assumptions and constraints that anchor the “local” analysis of the focal trait. However, given these assumptions, natural selection is assumed to act without constraint on the trait.