What happens to male nipples during sex

Why do men have nipples?

Whether male or female, at the beginning of our existence we are all the same. Human embryos only develop their sexual characteristics between the eighth and tenth week of pregnancy, because the Y chromosome stimulates the development of the testicles in boys. They form the sex hormone testosterone, which in turn ensures that the penis is created from the systems for the genitals. It also prevents breasts from developing later.

When the Y chromosome becomes active, it is too late to prevent nipples. Because they already arise in the phase in which the embryo does not yet "know" whether it will be a girl or a boy. As early as the sixth to seventh week, two milk bars are created that run from the armpit to the groin. Not only humans, but also all other mammals form milk ridges at this early stage of development.

This article is contained in Spectrum - Die Woche, week 46, 2009

In the course of the embryonic development, the milk ridge partially recedes: How much remains depends on the average number of offspring of a species. Humans and elephants keep two "teats", cows four and cats eight. But even with us it occasionally comes to polythelia, the formation of additional nipples, which can occur in both men and women. The additional warts are usually smaller and grow along the former milk ridges.

The fact that men have nipples can therefore be explained biologically. The question remains why evolution did not abolish male nipples. Charles Darwin proposed in "On the Origin of Species" the theory that in the very first mammals, both parents could have breastfed. However, science has so far found no evidence of this.

It may be more beneficial for the body to first create a basic blueprint for the embryo and then hormonally control which functions are activated. In addition, the nipples do not represent a selection disadvantage for their wearers. As long as the female mammals accept the round decorations on their males and still reproduce with them, the nipple will also remain a part of the male body.

In rare cases, men even seem able to breastfeed. In a report from 1859, Alexander von Humboldt mentions several fathers who spontaneously supplied their child with milk after their wife's death. Are such traditions just a myth? In principle, men have all the facilities for milk production, even if they are mostly stunted. And that breastfeeding virgins and adoptive mothers have also refuted that pregnancy must always precede milk leakage. In modern medicine, however, there are no longer any known cases of men giving milk.