Males gain weight while their mates are pregnant

In a recent study published in Biology Letters, researchers from the University of Wisconsin-Madison showed that male tamarins and marmosets—two monkey species known for their long tails and multicolored coats of fine fur—gain weight while their mates are pregnant. The researchers believe these monkeys put on the pounds to prime themselves for their future fatherly duties.

One researcher says all the males gained weight during a mate's pregnancy. Although the amount varied from monkey to monkey, the average gain was around a 10% increase in girth. Male monkeys also showed increased levels of hormones such as prolactin, estrogen and testosterone.

Human males also complain of weight gain during a partner's pregnancy. However, according to researcher, it is unclear whether the weight gain in humans serves the same biological purpose—storing energy for carrying and caring for infants—as it does in monkeys.

(I don't know why the researcher is so unclear on this. Isn't obvious that the men of our species are storing up the energy so that they can change baby diapers throughout the night ?).