Mixed models for the relationship between latitude, temperature, and human postcranial form

Abstract

AbstractObjectivesThe global distribution of human body proportions has long been attributed to thermoregulatory adaptation to climate. However, latitude has been the most common proxy for climate across ecogeographic studies. If thermoregulation was driving post‐cranial evolution, temperature should provide a better explanation for the morphological patterns observed than latitude, which encompasses temperature and other variables, as well as major events in human migration history. We investigate relationships between latitude, temperature, and postcranial form by distinguishing the strength of these potential selective factors from population structure.Materials & MethodsQuantitative genetic multivariate mixed models were used to estimate morphological effects associated with latitude, minimum temperature, and maximum temperature using osteometric data from 31 globally distributed groups, geographically matched genetic data from 54 groups, and geographically matched temperature data.ResultsDimensions reflecting body size (bi‐iliac breadth/femoral head size) show independent evolutionary responses from limb lengths. In models including population history, only dimensions reflecting body size show evidence of response to directional selection. Model results indicate that selection in response to minimum temperature has shaped evolution in body breadth and femoral head size. Models for limb length evolution accounting for population history match results of prior studies, but do not indicate responses to temperature‐driven directional selection.ConclusionsThis study highlights the importance of considering multiple potential sources of selection within a multivariate evolutionary model, demonstrating the possible synergistic effects of selective pressures. These results complicate the classic thermoregulatory model of human postcranial evolution and show that factors other than temperature may have shaped post‐cranial evolution in humans.