Rachael Anyim

The target of over 300 million years of natural selection, mammalian milk evolved to be sensitive to variation in the environment (e.g., mortality, resource scarcity) to confer advantages to growing infants. Milk constituents, like cortisol, relay information about mother-infant pairs’ shared environment to allow infants to curate appropriate responses and temperaments better suited to harsh, stressful conditions. The central aim of this proposal is to test predictions from life history theory that milk cortisol varies in its sensitivity to maternal physical and social environmental stressors. To investigate the function of milk cortisol for the mother-infant dyad, I will measure milk cortisol concentrations in specimens from lactating participants (N=75) recruited from upstate New York. In order to convey reliable cues to infants, milk cortisol should not fluctuate with day-to-day stressors; these likely would not prove useful in calibrating long-term development. Therefore, I hypothesize, from theory, that milk cortisol in fairly stable environments (e.g., the United States) will be robust to short-term stress but will transmit information to infants about more enduring stressors, and so should vary less with perceived stress and more with long-term maternal and environmental characteristics (e.g., maternal socioeconomic status, height/BMI). Indeed, this is what my preliminary data show.