Evolutionary fitness as a function of pubertal age in 22 subsistence-based traditional societies

Using a sample of 22 natural-fertility societies of mostly tropical foragers, horticulturalists, and pastoralists from Africa, South America, Australia, and Southeastern Asia, this study compares indices of adolescence growth and menarche with those of fertility fitness in these non-industrial, traditional societies.The average age at menarche correlated with the first reproduction, but did not correlate with the total fertility rate TFR or reproductive fitness. The age at menarche correlated negatively with their average adult body mass, and the average adult body weight positively correlated with reproductive fitness. Survivorship did not correlate with the age at menarche or age indices of the adolescent growth spurt. The population density correlated positively with the age at first reproduction, but not with menarche age, TFR, or reproductive fitness.Based on our analyses, we reject the working hypotheses that reproductive fitness is enhanced in societies with early puberty or that early menarche is an adaptive response to greater mortality risk. Whereas body mass is a measure of resources is tightly associated with fitness, the age of menarche is not.The age of puberty has fallen over the past 130 years in industrialized, western countries, where menarche age has receded from 16.5 years in 1880 to the current 12.5 years in western societies; this decline has occurred concomitantly with an improvement in child health [1]. The progressively declining age of thelarche and menarche may have multiple explanations. Primates' studies suggest a role for prenatal androgens and social factors (like the social rank) [2,3]. In the last decade, a popular notion among investigators is that early puberty may result from environmental exposure to endocrine disrupting chemicals (EDC), thus accelerating hypothalamic maturation [4]. Whereas EDC may have a bearing on the earlier age of thelarche, evolutionary forces may add a new angel to explain the secular trend in the age of m