Sexual Dimorphism in the Growth of Homo sapiens: Facts, Inferences and Speculation

Summary

Sexual dimorphism in body size is a common feature of most animal species. While in many species, the female is the larger sex, in mammals, males are commonly larger, and greater male body mass and height are typical of primates. Growth of H. sapiens, however, is characterized by a number of unusual features, including rapid in utero growth, a prolonged childhood phase, a pubertal spurt in stature, and a relative lack of sexual dimorphism, with adult male height averaging only 107% of that of females. The recent report of a female patient with a homozygous mutation of the gene for STAT5b, a critical component of the growth hormone (GH) signaling cascade responsible for insulin-like growth factor (IGF) gene transcription, has demonstrated that growth in both females and males is strongly pulsatile GH-STAT5b-IGF-dependent. This common dependence of both human females and males on the GH-STAT5b-IGF pathway may explain the relative lack of dimorphic growth characteristic of H. sapiens.