Leveling the Playing Field in Studying Cumulative Cultural Evolution: Conceptual and Methodological Advances in Nonhuman Animal Research

Cumulative cultural evolution (CCE), the improvement of cultural traits over generations via social transmission, is widely believed to be unique to humans. The capacity to build upon others' knowledge, technologies, and skills has produced the most diverse and sophisticated technological repertoire in the animal kingdom. Yet, inconsistency in both the definitions and criteria used to determine CCE and the methodology used to examine it across studies may be hindering our ability to determine which aspects are unique to humans. Issues regarding how improvement is defined and measured and whether some criteria are empirically testable are of increasing concern to the field. In this article, we critically assess the progress made in the field and current points of debate from conceptual and methodological perspectives. We discuss how inconsistency in definitions is detrimental to our ability to document potential evidence of CCE to nonhuman animals. We build on Mesoudi and Thornton's (2018) recently described core and extended CCE criteria to make specific recommendations about, from a comparative lens, which criteria should be used as evidence of CCE. We evaluate existing data from both wild and captive studies of nonhuman animals using these suggestions. We finish by discussing issues currently faced by researchers studying CCE in nonhuman animals, particularly nonhuman primates, and provide suggestions that may overcome these concerns and move the field forward.