Doctor of Philosophy

dissertationNatural selection favors individuals with those adaptive traits that maximize their reproductive success. Effective heat acclimatization in the desert requires conserving body water with a simultaneous reduction in body heat by engaging in adaptive strategic behaviors. The adaptive strategies in response to water and food deprivation that contribute to successful breast milk production among lactating desert women have not been adequately researched. This study compared the rates of energy expenditure between lactating and non lactating desert women in Hidalgo, Mexico, indicating a significantly consistent physiological reduction in the rate of energy expenditure among lactating women as compared to non lactating women. Time allocation data confirmed their exploitation of allomothers with the dominant help being provided by their older female children. The cooling of their bodies prior to breast-feeding, a behavior associated with the "hot breast milk" notion of the hot-cold syndrome, reduces their body heat and ensures maternal relaxation essential to successful breast milk synthesis. The influence of the hormone prolactin during lactation stimulated by increased frequency of breast-feeding, enhances their body water retention, thus improving the cost efficiency of breast milk production for these desert women with limited access to clean water. These adaptive behavioral and physiological strategies that improve infant nutrition and maternal hydration in hot dry climates might prove to be vital to human survival in a future of climatic change and ecological decline