The purpose of this study was to review published studies on the variabilit
y of age at menarche and age at menopause throughout the world, and to iden
tify the main causes for age variation in the timing of these events. We fi
rst present a summary table including mean (or median) values of the age at
menarche in 67 countries, and of the age at menopause in 26 countries. Gen
eral linear models showed that mean age at menarche was strongly linked to
the mean female life expectancy, suggesting that one or several variables r
esponsible for inequalities in longevity similarly influenced the onset of
menarche. A closer examination of the data revealed that among several vari
ables reflecting living conditions, the factors best explaining the variati
on in age at menarche were adult illiteracy rate and vegetable calorie cons
umption. Because adult illiteracy rate has some correlation with the age at
which children are involved in physical activities that can be detrimental
in terms of energy expenditure, our results suggest that age at menarche r
eflects more a trend in energy balance than merely nutritional status. In a
ddition, we found the main determinant of age at menopause to be the mean f
ertility, This study thus suggests that, on a large scale, age at menarche
is mainly determined by extrinsic factors such as living conditions, while
age at menopause seems to be mainly influenced by intrinsic factors such as
the reproductive history of individuals. Finally, these findings suggest t
hat human patterns cannot be addressed solely by traditional, small-scale i
nvestigations on single populations. Rather, complementary research on a la
rger scale, such as this study, may be more appropriate in defining some in
teresting applications to the practical problems of human ecology.