“Adaptationism” refers to a family of views about the importance of natural selection in the evolution of organisms, in the construction of evolutionary explanations, and in defining the goal of research on evolution.  Advocates of adaptationism or “adaptationists” view natural selection among individuals within a population as the only important cause of the evolution of a trait; they also typically believe that the construction of explanations based solely on natural selection to be the most fruitful way of making progress in evolutionary biology and that this endeavor addresses the most important goal of evolutionary biology, which is to understand the evolution of adaptations. An important alternative approach, “pluralism”, invokes historical contingency and developmental and genetic constraints, in addition to natural selection, as important causes of the evolution of a trait. Advocates of pluralism, or “pluralists” often also argue that the attempt to construct a natural-selective explanation of a trait is not the most fruitful way to make explanatory progress and that understanding adaptation is just one of several important questions in evolutionary biology. The “debate” over adaptationism is commonly understood to be the back-and-forth between adaptationists and pluralists.