Mother's milk made to order for boys, girls

Mothers may say they don't care whether they have a son or a daughter, but their breast milk says otherwise.

"Mothers are producing different biological recipes for sons and daughters," says Katie Hinde, an evolutionary biologist at Harvard University.

Studies in humans, monkeys and other mammals have found a variety of differences in both the content and the quantity of milk produced.

One common theme: baby boys often get milk that is richer in fat or protein — and thus energy — while baby girls often get more milk.