The Evolution of Childhood and Adolescence: Implications for Modern Human Origins
(University of Nevada, Las Vegas)
When did the modern pattern of life history evolve? Modern humans are characterized by having helpless, secondarily altricial newborns, a large neonatal and adult brain size, a childhood stage of growth, an adolescent growth spurt, and delayed reproduction. In particular, the duration of preadolescent growth in human is quite long so that sexual and physical maturation is substantially delayed to the end of the growth period. Dental and postcranial maturation in fossil hominins is used to assess the evolution of these life history traits. Fossil evidence indicates that secondary altriciality evolved late in the span of Homo erectus. The juvenile stage, particularly for Neanderthals, involved acquisition of adult skills as evidenced by muscle markings and trauma. Regression analyses of long bone dimensions demonstrate that growth spurts are present in both Neanderthal and early modern humans. However, an extension of the duration of growth, including a childhood stage, only evolved recently. These results highlight our unique life history and origins.