Abstract
ContextThe age of puberty has fallen over the past 130 years in industrialized, western countries, and this fall is widely referred to as the secular trend for earlier puberty. The current study was undertaken to test two evolutionary theories: (a) the reproductive system maximizes the number of offspring in response to positive environmental cues in terms of energy balance, and (b) early puberty is a trade-off response for high mortality rate and reduced resource availability.MethodsUsing 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.ResultsThe 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.ConclusionsBased 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.
Highlights
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]
When we tested the hypothesis that early adolescence is associated with increased reproductive fitness, the age at menarche and the growth indices did not correlate with the Interbirth interval (IBI) (Table 2)
The age at menarche did not correlate with total fertility rate (TFR) or reproductive fitness (NS: r = -0.208, p = 0.440; r = -0.008, p = 0.983, respectively), whereas the age at first reproduction correlated positively with the age at height spurt takeoff (r = 0.794, p = 0.003; Figure 2), peak height velocity (r = 0.791, p = 0.011), and return to takeoff height velocity (r = 0.765, p = 0.027), but TFR and reproductive fitness did not correlate with any of these variables (Table 2)
Summary
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]. Whereas EDC may have a bearing on the earlier age of thelarche, evolutionary forces may add This secular trend for early onset of puberty is a topic of much research interest. Heavy women in pre-industrial societies are more fertile, and both increased body weight and fertility are correlated with high birth rates [9]. This trade-off model has been used to predict that 18 years is the optimal age for first birth, which is near the observed average 17.5 years in such societies [10]
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