WHAT STABILIZES THE SEX-RATIO

It is suggested that the human sex ratio at birth is stabilized only t o a minor extent by the direct processes of natural selection. Instead the major factors stabilizing sex ratio seem to be behavioural (coita l rates) and psychological (parental perceptions of adult sex ratios). It is suggested that parental hormone levels are (a) a consequence of perceived adult sex ratios, and (b) a cause of sex ratio in the next generation, thus providing the basis for a negative feedback process s tabilizing the sex ratio.