Valuing Behavioral By-Products: Evolutionary Significance of Neutrally Drifting and Exaptive Cultures in Primates.

After challenging the view that cultural processes mainly produce behavioral adaptations, we urge researchers to adopt a pluralistic view on Darwinian evolution by emphasizing the diversity and importance of evolutionary by-products and highlighting the heuristic merit of concepts such as behavioral spandrels and exaptations, particularly in the domain of cultural evolution in primates. We then use the concept of the "structure-function interface" and draw from our own research on macaques to provide two examples of possible behavioral adaptations and their corresponding by-products, both of which are maintained via the proximate mechanisms of cultural processes and pleasurable feedback. These two behavioral by-products are female homosexual mounts and object play, and their putative functional counterparts are female-to-male mounts and tool use, respectively. We provide empirical evidence from the structural analysis of behavior to support our contentions that some non-conceptive sex cultures may neutrally drift from behavioral adaptations to by-products and that some object play cultures may exaptively afford tool use. Our approach dovetails with, and expands upon, a pluralistic perspective on evolutionary theory.