Sexual dimorphism is one of the main factors confounding attempts to generate sound alpha taxonomic hypotheses in the early hominin fossil record. To better understand how between-sex variation may confound alpha taxonomic assessments, we consider some of the factors that drive hard-tissue sexual dimorphism in extant primates. We review the socioecological correlates of body size sexual dimorphism, how sexual selection may be associated with craniofacial sexual dimorphism in the context of visual signaling, and how sex-specific patterns of growth and development in primates contribute to intra-specific variation. To illustrate how variation associated with inferred sexual dimorphism has the potential to confound alpha taxonomic assessments in early hominins, we focus on its impact on our understanding of a single taxon, Paranthropus boisei. We suggest that regions of the skeleton likely to be influenced by sexual selection should be avoided when generating alpha taxonomic hypotheses.

Keywords: Paranthropus; cranium; growth; primate; sex differences; skeleton.

© 2025 The Author(s). Evolutionary Anthropology published by Wiley Periodicals LLC.