Poor mothers in northern Kenya produce fattier milk for their daughters than for their sons, whereas those who are better off financially favour their sons over their daughters. The findings support a 1973 hypothesis that predicts that poor mothers will invest more resources in daughters, who stand a greater chance of increasing their status through marriage than do poor males. Conversely, mothers from wealthier families give more to their sons, who can pair with multiple females.
Masako Fujita at Michigan State University in East Lansing and her team assessed the fat content of milk from 83 mothers living in villages in which men can have multiple wives. The authors found that, when they controlled for factors such as age and dietary fat intake, mothers with less land and fewer livestock provided richer milk to their daughters than to their sons.
Am. J. Phys. Anthropol. http://dx.doi.org/10.1002/ajpa.22092 (2012)