Natural selection and the sex ratio

Abstract

Summary We have put Fisher's theory of the control of the sex ratio by Natural Selection on an analytic basis. This has enabled us to derive an expression for the selective advantage attached to reproduction with a given sex ratio, and to show that this depends on the sex ratio at the end of the period in which the offspring incur expenditure by their parents. It is this sex ratio which is probably stabilized near the value one‐half by Natural Selection. The rate of approach of a population to its equilibrium sex ratio depends on the available genetic variance in the sex ratio, and since this is probably small, evolutionary changes in the sex ratio of natural populations will almost certainly be too slow to detect.