Men may not be naturally wired to breast feed their babies but in certain circumstances, they may secrete milk too.
Although male lactation seems to be common only in dayak fruit bats, it is observed in a few domesticated animals, including cats, goats and guinea pigs, on rare occasions and in some cases even in humans.
In some male World War II prison camp survivors, who had suffered months of starvation, scientists found that after receiving adequate nutrition, their hormone-producing glands rebounded far quicker than their livers (which normally metabolise hormones), resulting in hormonal spikes that caused lactation.
A serious health condition called liver cirrhosis can also cause lactation by disrupting the organ's normal, hormone-metabolising function, a Live Science report said.
Health issues that affect the pituitary gland or the hypothalamus, which normally inhibits the release of prolactin, can also cause male milk production.
A 2010 study published in the Canadian Medical Association Journal documented lactation in a man with a pituitary tumour.