INTRODUCTION

Since the initial spread of Homo erectus from Africa some 1.8 million years ago, the human lineage has colonized every major ecosystem on the planet, adapting to a wide range of environmental stressors (Antón et al.,2002). As with other mammalian species, human variation in both body size and morphology appears to be strongly shaped by climatic factors. The most widely studied relationships between body morphology and climate in mammalian species are those described by “Bergmann's” and “Allen's” ecological rules. Bergmann's rule addresses the relationship between body weight (mass) and environmental temperature, noting that within a widely distributed species, body mass increases with decreasing average temperature (Bergmann, 1847). In contrast, Allen's rule considers the relationship between body proportionality and temperature (Allen, 1877). It finds that individuals of a species that are living in warmer climes have relatively longer limbs, whereas those residing in colder environments have relatively shorter extremities.

The physical basis of both of these ecological rules stems from the differences in the relationship between surface area (cm2) and volume (cm3 proportional to mass [kg]) for organisms of different size (Schmidt-Nielson, 1984). Because volumetic measurements increase as the cube of linear dimensions, whereas surface area increases as the square, the ratio of surface area (SA) to volume (or mass) decreases as organisms increase in overall size. In addition, metabolic heat production in all animals is most strongly related to body mass (e.g., Kleiber, 1975; FAO/WHO/UNU, 1985).