The role of behavior in evolution: a search for mechanism

Behavior has been viewed as a pacemaker of evolutionary change because changes in behavior are thought to expose organisms to novel selection pressures and result in rapid evolution of morphological, life history and physiological traits. However, the idea that behavior primarily drives evolutionary change has been challenged by an alternative view of behavior as an inhibitor of evolution. According to this view, a high level of behavioral plasticity shields organisms from strong directional selection by allowing individuals to exploit new resources or move to a less stressful environment. Here, I suggest that absence of clear mechanisms underlying these hypotheses impedes empirical evaluation of behavior's role in evolution in two ways. First, both hypotheses focus on behavioral shifts as a key step in the evolutionary process but ignore the developmental mechanisms underlying these shifts and this has fostered unwarranted assumptions about the specific types of behavioral shifts that are important for evolutionary change. Second, neither hypothesis provides a means of connecting within-individual changes in behavior to population-level processes that lead to evolutionary diversification or stasis. To resolve these issues, I incorporate developmental and evolutionary mechanisms into a conceptual framework that generates predictions about the types of behavior and types of behavioral shifts that should affect both micro and macroevolutionary processes.