title: Are human hands and feet affected by climate? A test of Allen's rule.
abstract: OBJECTIVE
  In recent years, several studies have shown that populations from cold, high-latitude regions tend to have relatively shorter limbs than populations from tropical regions, with most of the difference due to the relative length of the zeugopods (i.e., radius, ulna, tibia, fibula). This pattern has been explained either as the consequence of long-term climatic selection or of phenotypic plasticity, with temperature having a direct effect on bone growth during development. The aims of this study were to test whether this pattern of intra-limb proportions extended to the bones of the hands and feet, and to determine whether the pattern remained significant after taking into account the effects of neutral evolutionary processes related to population history.
  
  
  METHODS
  Measurements of the limb bones, including the first metatarsal and metacarpal, were collected for 393 individuals from 10 globally distributed human populations. The relationship between intra-limb indices and minimum temperature was tested using generalized least squares regression, correcting for spatial autocorrelation.
  
  
  RESULTS
  The results confirmed previous observations of a temperature-related gradient in intra-limb proportions, even accounting for population history. This pattern extends to the hands, with populations from cold regions displaying a relatively shorter and stockier first metacarpal; however, the first metatarsal appears to be wider but not shorter in cold-adapted populations.
  
  
  CONCLUSIONS
  The results suggest that climatic adaptation played a role in shaping variation in limb proportions between human populations. The different patterns shown by the hands and feet might be due to the presence of evolutionary constraints on the foot to maintain efficient bipedal locomotion.
authors.affiliation: Centre for Research in Evolutionary and Environmental Anthropology, Department of Life Sciences, University of Roehampton, London, SW15 4JD, UK.
authors.forename: Lia
authors.initials: L
authors.lastname: Betti
authors.affiliation: Department of Anthropology, University at Buffalo, SUNY, Buffalo, NY, 14261.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lycett
authors.affiliation: Department of Anthropology, University at Buffalo, SUNY, Buffalo, NY, 14261.
authors.forename: Noreen
authors.initials: N
authors.lastname: von Cramon-Taubadel
authors.affiliation: Department of Anthropology, University of New Mexico, Albuquerque, NM, 87131.
authors.forename: Osbjorn M
authors.initials: OM
authors.lastname: Pearson
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000885:Anthropology, Physical; D002980:Climate; D005528:Foot / Q000033:anatomy & histology* / Q000502:physiology; D006225:Hand / Q000033:anatomy & histology* / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D044469:Racial Groups / Q000706:statistics & numerical data*; D013696:Temperature
keywords: cold adaptation; neutral variation; phenotypic plasticity; selection