Female biological resiliency: Differential stress response by sex in human remains from ancient Nubia

This research presents male-female differences in stress response evidenced in human remains from the Medieval site of Kulubnarti in Sudanese Nubia. This analysis is unique in that a direct comparison of subadult males and females is rarely possible using archaeological remains. Rather, such analyses invariably rely on evidence of subadult differences retained in adult (sexable) skeletons. In the case of Kulubnarti, natural mummification has made it possible to measure sex-specific differences among subadults as well as adults following five avenues of investigation: 1) mortality, 2) growth and development, 3) enamel hypoplasia, 4) cribra orbitalia, and 5) cortical bone maintenance. A comparison of mean life expectancy (eox) values for males and females aged 10–55+ years revealed a consistent pattern of greater female survivorship, particularly in childhood (age 10 category) where female life expectancy exceeds that of males by 19%. Measures of growth and development, enamel hypoplasia, cribra orbitalia, and cortical bone loss were subsequently used to test a hypothesis of greater female resiliency based on the mortality data. Male-female differences in skeletal maturation are pronounced with male skeletal ages averaging a significant 2.9 years below their dental age. Females show no significant differences with an average skeletal age 0.75 years ahead of dental age. Males begin hypoplasia formation one year earlier than females and, prior to age four, average 18% more hypoplasias (p<0.05). Also, by age 8, males have on average more than twice the frequency of cribra orbitalia (p<0.05). In contrast to their consistent pattern of reduced childhood stress, adult females lose significantly more cortical bone than their male counterparts and have less cortical bone across the adult age range. Nevertheless, females outnumber males of all ages with a sex-ratio below but parallel to that observed in modern populations. The rapid age-related reduction in males relative to females, even in old age, suggests a continuing female resiliency in spite of their greater rate of osteopenia and may reflect a reproductive advantage to the population through heightened female survival and adaptability.