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Animal moms customize milk depending on baby's sex

A special blend of mother's milk just for girls? New research shows animal moms customize their milk in surprising ways depending on whether they have a boy or a girl.

The studies raise questions for human babies, too, about personalizing formula and even about the donor milk that's used for hospitalized preemies.

Pediatricians have long stressed that breast milk is best for babies. But Harvard University evolutionary biologist Katie Hinde says her research shows it's a myth that mother's milk is pretty standard.

She said Friday that monkeys make richer milk for sons but more milk for daughters. The girls' milk contains more calcium, presumably for their faster-maturing bones. There also are gender differences in how the monkeys respond to a stress hormone in mom's milk.