Natural selection and the origin and evolution of weeping in man.

Tearless crying in the young of early man, with an increased dependency period, would repeatedly have caused dehydration of the mucous membranes, and thus have rendered them vulnerable to the insults of the environment. Tears are bacteriostatic as well as moistening. The hypothesis is advanced that natural selection favored those infants who could produce tears, and that in this way the function became established in man.