1Department of Biological Anthropology, University of Cambridge, 2Child Health Evaluative Sciences, The Hospital for Sick Children, Toronto, Ontario, Canada, 3Department of Medicine, School of Medicine, Universidad Peruana Cayetano Heredia, Lima, Peru, 4Institute of Child Health, University College London, UK
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The thrifty phenotype hypothesis has had a major influence on research into growth trade-offs under conditions of environmental stress. While brain-sparing growth is often referenced, the existence of growth trade-offs influencing relative trunk and limb proportions has not been explicitly considered. Given documented associations between relative leg length, childhood environment and adult disease risk, elucidating how and when body proportions are determined is important for understanding these associations and the process of adaptation to environmental challenges during growth.
We explored relative limb length, trunk length, head circumference and limb segment lengths (upper arm, thigh, ulna, tibia, hand and foot) in a cross-sectional sample (n=447) of highland and lowland Peruvian children aged 0.5-14.5 years. Highland children experience greater environmental stress than lowland children. Population differences in relative limb and trunk proportions exist from 0.5 years of age. Highland children have significantly shorter limbs relative to trunk length than lowland children. Within limbs, distal limb long bones (ulna and tibia) show greater reduction in relative length among highland children than proximal long bones or the hand and foot. Head circumference shows the smallest population differences.
The results suggest that the brain and major vital organs of the trunk are relatively protected from stress-related growth restriction at the expense of limb (and particularly distal long bone) length. Hand and foot length are relatively protected compared with the rest of the limb, perhaps for functional reasons. These results support the extension of the thrifty phenotype hypothesis to patterns of limb growth in humans.
EP received PhD funding from the Arts and Humanities Research Council (UK), and fieldwork grants from the University of Cambridge Centre for Latin American Studies Abbey-Santander Travel Grants.