Breastfeeding, the Australian Broadcasting Corp tells us, is a little more bespoke than one might expect:
“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.
It’s not yet clear why human mothers produce such different milk for their babies, says Hinde.
There is evidence, however, that the stage is set while the baby is still in utero.
Hinde published a study last week that showed that the sex of the foetus influences the milk production of cows long after they are separated from their calves &emdash; typically within hours of the birth.
The study of 1.49 million cows found that, over the course of two 305 day lactation periods, they produced an average of 445 kilograms more milk when they had female calves than when they had males.
They also found no difference in the protein or fat content of the milk produced for heifers than for bulls.