Bone functional adaptation does not erase neutral evolutionary information

OBJECTIVES: To investigate whether diaphyseal and craniofacial variation similarly reflect neutral genetic variation among modern European and South Africans. MATERIALS AND METHODS: Diaphyseal and craniofacial data were collected on English, South European, and South African samples. The Relethford-Blangero model was used to compare predicted among-population relationships generated by limb bones relative to those generated by the crania and, further, to test whether adaptive plasticity affected these predicted relationships. Evidence of adaptive plasticity was confirmed by comparing J, an indicator of limb bone robusticity, among individuals who worked different occupations in industrializing Lisbon (Portugal) and Bologna (Italy). RESULTS: Diaphyses were more variable than were crania and more robust in individuals with physically demanding occupations-both consistent with expectations of adaptive plasticity. However, diaphyseal variation still generated among-population relationships consistent with neutral genetic predictions and Mantel tests confirmed a high, significant correlation between diaphyseal and craniofacial distance matrices. This pattern was not strongly affected by adaptive plasticity. DISCUSSION: Among-population patterns of diaphyseal variation are consistent with neutral expectations and are consistent with historical data on population composition, genetics, and migration. Furthermore, plasticity induced by Industrial-era levels of physical activity does not erase these neutral signatures. Diaphyseal variation may therefore be useful to infer neutral (presumably genetic) information across populations, and controlling for existing relationships may strengthen inferences of physical activity made when comparing limb bone structure across populations.