Cycles of sex examined for environmental influences.

Abstract

Participants from around the world gathered to discuss Human Reproductive Ecology: the Interactions of the Environment Fertility and Behavior on May 21-24 1993 in Research Triangle Park North Carolina. This paper summarizes the topics discussed: swinging sperm counts according to season the seasonal cycles of births and the relationship between female body fat and menstrual cycles. Findings were presented by Richard Levine on the high concentration of sperm in the summer and a peak of 10% above the average in February and March. There is low concentration of sperm in the summer and a peak of 10% above the average in February and March. There is low concentration in late summer which corresponds with low birth rates in April and May. Anthropologist James Wood reported evidence which showed that reduced sperm counts were not related to a longer waiting time before conception. Levines findings also showed that heat was not a factor. Births also follow a seasonal pattern. In the US there are birth peaks in September and birth lulls in April and May. Other seasonal patterns are evident around the globe but as seasonal patterns change so do birth patterns. Demographer David Lam investigated the heat hypothesis as an explanation for birth patterns and found not relationship between heat controlling for air conditioning and birth patterns 9 months later. Accepted understanding of the relationship between body fat and amenorrhea was challenged by findings of endocrinologist David Cummings who showed that low caloric intake was the cause of amenorrhea among female athletes. Cummings remarked that it was easier to accept a simple falsehood over a complex truth. The exact relationship between nutrition and menstruation is not known.