Sven Michael Kasser , Laura Fortunato, Kevin N. Lala

Gene-culture coevolution (GCC) stands out among approaches to human evolution for its ambitious synthesis of biological and social sciences. Combining insights from cultural evolution and human genetics, it has been invoked to explain the evolution of many "species-defining" human traits, from language to large-scale cooperation. However, despite its broad conceptual appeal, empirical evidence for GCC is often perceived as limited to a few "classic" examples, such as lactase persistence. We propose that this apparent gap between theoretical significance and empirical support may partly derive from conceptual ambiguities about what kind of gene-culture interactions truly constitute gene-culture coevolution. Drawing on recent work on gene-culture coevolution in animals and examples from the human genomics literature, we argue that a broader conception of gene-culture coevolution, explicitly incorporating drift and migration, provides a more comprehensive understanding of human evolutionary dynamics. Our approach, which we term "broad gene-culture coevolution," builds upon and subsumes the existing "narrow" framework that primarily emphasises selective processes. We illustrate the utility of this expanded perspective through two case studies: the evolution of skin pigmentation and the influence of trade networks on genetic variation in Melanesia. By integrating insights from anthropology, genetics, and cultural evolution, we demonstrate how cultural factors can shape both adaptive and neutral genetic variation and population structure. This broader framework not only accommodates a wider range of empirical findings but also opens new avenues for hypothesis generation and testing in the study of human biocultural evolution. We conclude by discussing the boundaries of this approach and its potential to synthesise diverse disciplinary perspectives, ultimately providing a more nuanced understanding of how humans have shaped their own evolution.