Subjective life expectancy predicts offspring sex in a contemporary British population.

There is evidence that women who are in poor physical condition or who reside in deprived environments are more likely to give birth to daughters than to sons. Under deprived environmental conditions, or when in poor physical health, it has been hypothesized that parents should take into account the available resources and manipulate the sex of any children born. Using subjective life expectancy (SLE) as a measure of how an individual views their future health and environment, I demonstrate that there is an association between the sex of the first child and SLE in a sample of mothers from a contemporary British population (Gloucestershire, UK). SLE was a significant predictor of offspring sex: women who believed that they had longer to live were more likely to have had a male birth than women who thought they would die earlier. Detection of such a bias among the children of British mothers may provide evidence that the sex ratio under relatively affluent Western conditions can still be influenced by adverse environmental or poor maternal condition.