Human cranial anatomy and the differential preservation of population history and climate signatures

Abstract

Cranial morphology is widely used to reconstruct evolutionary relationships, but its reliability in reflecting phylogeny and population history has been questioned. Some cranial regions, particularly the face and neurocranium, are believed to be influenced by the environment and prone to convergence. Others, such as the temporal bone, are thought to reflect more accurately phylogenetic relationships. Direct testing of these hypotheses was not possible until the advent of large genetic data sets. The few relevant studies in human populations have had intriguing but possibly conflicting results, probably partly due to methodological differences and to the small numbers of populations used. Here we use threedimensional (3D) geometric morphometrics methods to test explicitly the ability of cranial shape, size, and relative position/orientation of cranial regions to track population history and climate. Morphological distances among 13 recent human populations were calculated from four 3D landmark data sets, respectively reflecting facial, neurocranial, and temporal bone shape; shape and relative position; overall cranial shape; and centroid sizes. These distances were compared to neutral genetic and climatic distances among the same, or closely matched, populations. Results indicate that neurocranial and temporal bone shape track neutral genetic distances, while facial shape reflects climate; centroid size shows a weak association with climatic variables; and relative position/orientation of cranial regions does not appear correlated with any of these factors. Because different cranial regions preserve population history and climate signatures differentially, caution is suggested when using cranial anatomy for phylogenetic reconstruction. Anat Rec Part A, 288A:1225-1233, 2006. 2006 Wiley-Liss, Inc.Key words: craniofacial morphology; population history; neutral genetics; climate adaptation; human variationCranial morphology is commonly used to reconstruct hominin phylogenies and population histories (e.g

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

“…However, the high Fst values observed in these variables were mostly influenced by populations living in the northernmost regions of the planet, i.e., extreme North America, Northeast Asia, and Northern Europe. This result agrees with previous studies that found no correlation between climate and cranial morphology once Arctic samples were removed from the analyses and that suggested that climatic adaptation was observed in populations living under extreme cold conditions (Roseman, 2004;Harvati and Weaver, 2006b). …”

“…Nonetheless, the facial measurements in the present study were found to be correlated, albeit more weakly than neurocranial measurements, with geographic distances as well as with climate. This result supports the recent finding by Smith (2009), who reported that facial morphology was correlated with neutral genetic distances (contra Harvati and Weaver, 2006b).…”

“…High Fst values, pointing to diversifying selection, are apparent in the northernmost populations of Europe, Asia, and America. This pattern has been previously observed for North American groups (Roseman, 2004;Harvati and Weaver, 2006b) in much smaller samples (10-13 geographic population samples, comprising one Arctic sample each). Although natural selection to cold climate seems to have been a considerable force of morphological differentiation among modern humans, it appears limited to northern populations and has not eliminated the geographic, population history, signal observed in the overall pattern of modern human craniometric differentiation.…”

Global human mandibular variation reflects differences in agricultural and hunter-gatherer subsistence strategies

“…In recent decades, it has become clear that the majority of modern human cranial shape variation is congruent with a null model of neutral evolution, with relatively few morphological regions being subject to diversifying selection (e.g., [10][11][12][13][14][15][16][17][18][19]. However, there appear to be two major exceptions to this general pattern.…”

“…However, there appear to be two major exceptions to this general pattern. Aspects of facial morphology, and particularly nasal morphology, are likely to have been subject to diversifying natural selection in response to climatic conditions (11,(20)(21)(22), which would explain why facial shape is correlated with climate when cold-adapted populations are included (13,18). Second, it has been found (14,15) that global patterns of mandibular variation do not follow a model of neutral evolution.…”