Sex ratio, coital rate, hormones and time of fertilization within the cycle

In this paper I shall consider the relationships between coital rates, timing of fertilization within the cycle, and sex ratios of the resulting offspring. It will be suggested that there is: (1) Analytic (mathematical) evidence for a correlation between coital rate and time of fertilization. (2) Empirical evidence for a correlation between time of fertilization and sex ratio of offspring. Whence there arises: (3) A correlation between coital rate and sex ratio secondary to correlations of both with time of fertilization. These variables will be considered in these pairs in order. Section 4 will be devoted to the magnitude of the correlation between coital rate and sex ratio. Lastly it will be noted that the data on these two variables cohere not only with that on timing of insemination, but with the overall hypothesis that parental hormone levels at conception are causally associated with sex ratios at birth.