As our closest living relatives, chimpanzees have often served as models to help reconstruct early hominin behavior. However, despite documented behavioral variation at the species and subspecies level, we still know little about how skeletal variation relates to behavior among living chimpanzees. This is especially important in light of increasing evidence that early hominins engaged in a variety of locomotor modes involving mixtures of arboreal and terrestrial behaviors:​ previous studies have often focused on broad taxonomic and behavioral groups, but closely-related modern taxa with subtle behavioral differences may provide better models. Studies of ontogenetic trajectories within groups can also serve as "natural experiments" for testing the relationship of morphology to known behavioral changes with age while controlling for genetic heritage.

This study compares skeletal morphology with field observational behavioral data among bonobos and the individual subspecies of common chimpanzee. Aspects of skeletal morphology previously hypothesized to reflect locomotor behavior, including bone lengths, articular proportions, phalangeal curvature and dorsal metacarpal and metatarsal ridge (DMR) morphology, and cross-sectional structural properties (e.g. interlimb strength proportions, diaphyseal shape ratios), were compared both across adult P. paniscus and P. troglodytes subspecies and during ontogeny. These results were then contextualized in existing data on locomotor behavior frequencies in these same taxa. Bone lengths and articular proportions were hypothesized to primarily reflect genetic differences and thus mainly vary along phylogenetic lines, while internal cross-sectional geometry, phalangeal curvature, and the DMR were predicted to show greater concordance with behavior regardless of phylogenetic relationships.

Results suggest that, even at these narrow taxonomic levels, length and articular proportions primarily vary along taxonomic lines, distinguishing P. paniscus from other Pan, while cross-sectional geometry and phalangeal curvature show more differences between P. troglodytes subspecies and are more consistent with differences in frequencies of locomotor behavior. Dorsal metacarpal ridge morphology seemed to be related both to body size and to behavior. This increased understanding of the relative importance of genetic inheritance and developmental plasticity in the production of adult skeletal features in Pan informs both our understanding of the functional anatomy of living hominoids and our interpretations of morphological variation in fossil hominins