Determinants of infant carrying behavior in rural Papua New Guinea.

Mothers vary the amount of carrying based on assessment of infant and local environmental conditions. Age and milestone attainment are equally predictive of time on the ground and therefore increased exposure to antigens, pathogens and other dangers. High levels of infant carrying function as offspring protection by increasing exposure to ground level pathogens gradually, thus allowing for the naïve immune system to develop immunocompetence incrementally.