Seasonal rhythm of menarche as a sensitive index of living conditions.

The paper is focused on the seasonal pattern of birth and occurrence of menarche in different populations. The material collected in 1988/89 consists of 522 girls and their 249 mothers from schools of Merida, and of 135 girls and their 66 mothers from Progreso (Yucatan, Mexico). Occurrence of a biorhythm due to which girls matured in the month of their birth more frequently than by chance, was found. A shift of the maturation to an earlier or later month is caused by stress acceleration up or delaying maturation. Seasonal differences in menarche occur in different climates, but they depend on seasonal differences in the life style, occupation, and the like, rather than on climate itself. Typically menarche occurs in the extreme periods in terms of climate, diet, hard work, stress, etc., that is, in summer and/or in winter. The age of mother's maturation is correlated with that of daughter's. Month of daughter's maturation is correlated with that of mother's. Correlation exists between the month of woman's birth and the month of her maturation. No correlation exists between the month of daughter's birth and that of mother's, and between the month of daughter's maturation and the month of mother's birth.