This photo provided by the California National Primate Research Center shows a nursing rhesus macaque monkey in 2013. In a study of hundreds of milk samples, researcher Katie Hinde of Harvard University found that nursing rhesus macaque monkeys made different milk for daughters versus sons. Scientific insights to mother’s milk might someday help doctors provide better advice to nursing mothers, or suggest ways to improve infant formula. The studies raise questions for human babies, too, about how to choose the donor milk that's used for hospitalized preemies, or whether to explore gender-specific infant formula. (AP Photo/California National Primate Research Center, Kathy West)WASHINGTON (AP) — A distinct mix of mom's milk only for women? New research shows animal mothers are customizing their milk in stunning methods depending on whether or not they’ve a boy or a lady.