Evolutionary biologists and psychologists have long been aware of maternal effects on the secondary sex ratio in mammals. Up till now these have appeared inconsistent but re-analysis of the evidence, focusing on normally distributed maternal testosterone and its physiological and behavioral sequelae, reveals some support for the existence of sex-of-offspring differences between mothers. In addition to the animal studies showing a relationship between maternal, testosterone-based dominance and

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... e secondary sex ratio, research on human mothers shows sex-of-offspring differences in a range of testosterone-related attributes (physiological, behavioral and cognitive) measured at varying times from before the child was conceived to the mother's maturity. Further exploration of these differences might help elucidate the problems surrounding sex determination in mammals.