Insights into the evolution of child growth from Lower Pleistocene humeri at Venta Micena (Orce, Granada province, Spain)

Well-defined human anatomical characteristics are present on humeral fragments of a child (VM-1960) and an adult (VM-3691) from early Lower Pleistocene sediments at Venta Micena: both have narrower medullary cavities than in African Homo erectus/ergaster (KNM-ER 1808), and the child's humeral shaft is longer than in recent 8-to-9-year-olds even though its muscle markings are less pronounced than theirs. We infer that exposure of growing children to high mechanical loading favoured Plio-Pleistocene skeletal evolution in Homo of humeral robusticity and elongation. Precocious childhood arm-bone development, occurring before pubertal growth-spurt increments in shoulder and arm muscularity, implies a different balance from today between prepubertal hormonal influences exerted on ossification (growth hormone and somatomedin C) and the adolescent gonadal hormones of our modern growth spurt which may have still been in the process of evolution by natural selection.