Breastfeeding is biologically possible, but is it desirable?

Today, fathers and mothers tend to share early parenting responsibilities more than before, but there is one biological difference that seems difficult to overcome: breastfeeding . However, men do have nipples and, in rare cases, are also capable of producing milk. Would it be science fiction if they too would one day breastfeed their offspring?

The phenomenon has antecedents. In extraordinary circumstances, some men have breastfed their babies. The Talmud recounts the case of a man who developed breasts and breastfed his child when the mother was gone. The German naturalist Alexander von Humboldt documented in the 19th century that near Cumaná, Venezuela, another man managed to do so for three months. History offers more recent examples: in 2002, in Sri Lanka, a widower stimulated his nipples until they secreted enough milk to feed his daughters.

There are medical compendiums from the 19th century that refer to the phenomenon, and even Charles Darwin mentions it in The Descent of Man (1871):

"It is well known that rudimentary mammaries exist in all male mammals, including humans. In several cases, these have developed remarkably and produced an abundant supply of milk."

Indeed, male breast tissue is potentially functional. However, under normal hormonal conditions, a man's ability to breastfeed is dormant.

During World War II , prisoners who had suffered extreme starvation suffered from galactorrhea—abnormal milk production—when they resumed eating. Their liver, testicles, and pituitary gland were atrophied by starvation. Upon recovery, levels of prolactin, a hormone key to lactation, increased.

Other medical conditions can trigger the process. Tumors in the pituitary gland, for example, increase the production of prolactin.

The obstacle to male lactation, then, is not anatomical but hormonal.

Evolution explains why male mammals do not breastfeed. Breastfeeding provides a secure source of nourishment for their young and protects them from the harsh environment, but it comes at a high energy cost: about 500 calories a day in humans. Females invest enormous resources in gestation, and lactation is a natural extension of this process.

In males, however, such an expenditure of energy is unjustified. Uncertainty about paternity is also crucial, since males in most mammals are unsure of their genetic link to their offspring. Investing resources in offspring that might not be theirs makes no evolutionary sense.

Sexual competition is another factor to consider. Selection has favored the ability of male mammals to fertilize multiple females to perpetuate their genes, but it does not reward paternal care. This is observed in less than 10% of species, while it is common in birds.

There are exceptions: male Bornean Dayak bats secrete milk, albeit in small quantities. The phenomenon has also been documented in primates under stress.

This reveals that evolution hasn't favored lactation in males, but it hasn't eliminated it entirely either. Male nipples can be activated. It's as if a switch were turned off. With relatively simple hormonal pharmacological interventions, men could breastfeed. The question is whether this would be desirable.

Ethical debates surrounding the use of biotechnology to modify humans are intense. Proponents of transhumanism assert that we have the right (and even the duty) to improve our biology, while critics warn of the risks of doing so. As philosopher Antonio Diéguez points out in Pensar la Tecnología (Thinking Technology) (2024), these interventions require deep reflection on their consequences.

In the case of male breastfeeding, there are good arguments in favor .

When the nipple is stimulated, the body releases oxytocin. This hormone, which generates feelings of calm, intimate connection, and social harmony, facilitates deep emotional bonds between mother and baby. The effect is believed to be replicated in breastfeeding men and would surely strengthen the father-child relationship.

Research also shows that testosterone decreases in men involved in parenting. Although the relationship between this hormone and violence is complex, males with elevated testosterone tend to be more dominant and competitive. Breastfeeding could result in more empathetic and cooperative men . Given that male violence is still a serious problem, this transformation would have social benefits.

The most compelling argument is that it could balance the biological burden of reproduction. From pregnancy to breastfeeding, this is the cause of social, economic, and political inequalities. Even today, in countries with better equality policies, women are the primary caregivers in early childhood. Shared breastfeeding would be a step toward real equality.

There would also be benefits for new family forms. Today, family configurations that were previously unthinkable have gained a sociopolitical place: same-sex couples, single parents, and non-traditional families. Breastfeeding by males would allow homosexuals and transgender people to raise their children with all the advantages of breast milk.

There is another positive cultural shift. Breastfeeding has been invested with a sacredness that transcends biology, as depicted in images of the Virgin Mary in Christian art, a symbol of purity and selflessness. Sharing breastfeeding would challenge this cultural construct, which has idealized the female body as a source of nourishment, and free it from superhuman expectations. Allowing men to breastfeed would allow breastfeeding to be recognized as an act of care, not tied to an essential identity.

From a medical perspective, the side effects of modifying the delicate male hormonal system should be studied. Any endocrine disruption can have consequences that require thorough evaluation.

In the ethical realm, questions arise about the limits of our intervention in biology. Are we playing "god" if we try to modify our sexual nature? Bioconservatives such as Francis Fukuyama, Michael Sandel, and Leon Kass maintain this view, and their arguments deserve consideration.

Breastfeeding challenges our concepts of masculinity, fatherhood, and gender roles. Resistance would certainly be strong, as with any major social change. But history teaches us that one generation views what is normal as unnatural to the next.

Humanity has always used technology to overcome its biological limitations. Perhaps it's time to apply that ingenuity to one of the most basic aspects of the human experience: feeding and bonding with our offspring in their first, crucial months of life.

Few innovations promise such a beneficial impact on our species.

This article was written in collaboration with philosopher and writer Sandra Caula.

Article published in The Conversation.