When it comes to rearing babies, females are given the brunt of the work. We not only hold the little bubs for nine-months while they develop. But females are also responsible for lactating the newborn after it’s born. In sharp contrast, when it comes to fellas – all they need invest is a single ejaculate.

This inequality isn’t a human phenomenon. Males directly care for offspring in less than 10 per cent of mammal species, which begs the question:  why do female mammals get the lion’s share of the parental burden? And if males wanted to, could they share the load?

I’m not talking about changing the diaper; I want to know could men lactate?

Darwinian developments

Evolutionarily speaking, there are two reasons that might explain why males haven’t evolved to lactate. One: since babies grow inside the female, males can never be certain that it’s their child they’re caring for. Why expend all that milk for a child that isn’t your DNA? And two, since females are carrying the baby it might be advantageous (for the species) if the male ran off and impregnated another women instead of waiting around for the baby to get thirsty.

But, there are some good reasons that sticking around. Blokes could protect the vulnerable mother in the latter stages of pregnancy. And, it’s been noted that in dogs litter size often matches the amount of milk females can produce. If males developed to lactate, maybe larger litter sizes could develop.

Could guys do it?

We used to think that being pregnant made women lactate, and since blokes couldn’t get pregnant, we figured they couldn’t lactate either. But this isn’t true. It’s the hormones and manual suckling that gets milk flowing. It’s not surprising then that in female animals, lactation can be induced without pregnancy through injecting hormones and/ or suckling.

In theory men just need to make the right hormones, not babies, to start producing milk. And here’s the kicker: men can make the right hormones, and they can produce some milk.

Why do women make milk?

Milk is released from nipples through a hormone called prolactin. During the later parts of pregnancy, levels of prolactin rise. But women don’t release milk until the baby is born because the effect of prolactin is blocked by high levels of progesterone that a mother-to-be is making. At childbirth, levels of progesterone fall, and milk starts secreting from nipples.

According to a 2008 review on male lactation men can make prolactin and even have spontaneous surges of the hormone that reach the same level as females in late pregnancy.

Suckling Swedes

Once lactation begins after childbirth, levels of prolactin in females drop. But nipple suckling from the baby stimulates more prolactin to be released, ensuring a continuous supply of milk.

Manual nipple stimulation can also increase prolactin levels in men. This is good news for Ragnar Bengtsson, a 26 year old man from Sweden, who is currently stimulating his breasts using a breast pump every three hours for three months in an attempt to lactate.

According to the Daily Telegraph, Sigbritt Werner, professor of endocrinology at Karolinska Institutet in Stockholm, said that if he keeps this up a layer of tissue will begin forming beneath the nipple and enough prolactin will be made to release “a drop or two” of milk.

Why only a drop or two?

Milk is stored inside in little sacs inside breasts called alveoli. So to store milk, you need breasts. To make breasts (naturally) you need oestrogen and progesterone, and importantly you need to not have testosterone, which blocks breasts developing. When testosterone levels rise during puberty in males, the actions of typical female hormones on breasts is stopped, so men don’t have the milk storage capacity of women.

But guys can make some milk! So do they ever do it?

Yes! Following disease and deprivation men have actually been observed lactating. Malnourished men in World War II prisoner of war camps lactated after they were liberated and given proper sustenance. Why?

The long term starvation severely damaged their liver, testicles and pituitary gland. But when the men were given nutrition the function of the testes and pituitary gland improved quite quickly, and started doing their job – which is making hormones.

It’s usually the liver’s task to breakdown these hormones if the body doesn’t need them. But the liver recovered from starvation much slower than the other organs. This meant there was a hormonal imbalance that caused men to lactate.

For similar reasons, men with liver cirrhosis and cancers around the pituitary gland have also been observed lactating.

Is it really lactation?

US academics Racey and Racey argue that lactation can only be used to describe milk production that is used to feed offspring. So when men produce a little drop of milk following famine, disease and manual suckling it’s not “lactating”, but a condition called galactorrhoea.

Unfortunately, while men can produce and release milk, there is no male mammal species on the planet that has been shown to produce it in large enough quantities to sustain a newborn’s growth. For some reason, evolution has entrusted lactation to female mammals around the world. And I guess we ought to embrace it.

Cookies anyone?