Women who are dominant are more likely to have sons. Demographic studies show that more male children are born after wars, yet most people believe that their baby's sex is a matter of chance - determined by the father's sperm. Valerie Grant presents evidence that the mother's personality - which is related to female testosterone levels - can actually influence which type of sperm fertilises the egg.

Using data from human and animal studies Valerie Grant discusses the implications for human evolution, developmental psychology and reproductive biology. Her claims are controversial and the implications of her findings far reaching. Whether mothers have sons or daughters may not be a matter of chance. It may depend on which sex infant the mother is more suited to raise.