Effect of aging on sexual dimorphism of the human skeleton: A multivariate analysis

Abstract

The well-known pubertal acceleration of growth leads to the high morpho-physiological differentiation between males and females, allowing them to fit the requirements of biological reproduction and specifically adult activities. In human beings, pubertal differentiation process ends at about 20 years of age. Further studies suggest that secondary diverse activities related to differential growth and sexual dimorphism ?differential growth in soft tissues, physiologically or pathologically conditioned osseous modifications, etc- are evident. The aim of the present study is to find out whether a "late sexual dimorphism" - specifically in the maturity-elderly transition - actually exists in humans. Ninety-nine skeletons of Caucasoid subjects well registered as to age and sex at the time of their death, were studied. The sample was divided into four groups: 1) twenty-six mature 40-59 year-old males; twelve mature 40-59 year-old females; 3) forty-six senile 60-90 year-old males; 4) twelve senile 60-90 year-old females. The femoral, tibial, fibula, radial, cubital, neurocranial, and facial lengths, the neurocranial, facial, orbitary, and nasal widths, ad the neurocranial, facial and orbital heights were measured. Discriminant (backward stepwise) and canonical analysis were made, and Euclidian distances for hierarchical clusters were calculated. After data standardization, the lowest multivariate F-value was found in the senile-mature female comparison and the highest in the mature male-senile female comparison. They were followed by the senile male-senile female, mature female-senile female, mature male-senile male, and mature male-senile male ones. The most sensitive variables were the cubital length, nasal width, and orbit height. Changes in size and shape affected late sexual dimorphism. When the size effect was gone, new sexually dimorphic phenomena based on growth/decrease rates could be observed in elderly subjects. The dynamics of the late sexual dimorphism is different from that of the puberty. The main subject is the non linear reduction of variables linked to bones (shape changes), which, in turn, may obey the selective bone resorptions associated with the catabolic estrogeny of the senile female crania.