The human body has long been a subject of curiosity, but you may be surprised to learn that in terms of evolution, mice could actually be more highly evolved than men in one certain regard – nipples. Whereas men develop a pair of nipples that serve no purpose other than offering slight interest on the chest area, male mice don’t have these markings. In fact, among stallions and male platypuses, mice are among a small cluster of mammalian species that don’t leave the womb with nipples. During early pregnancy, both male and female mice embryos form mammary tissue, which is the foundational tissue that becomes fully-fledged nipples.
In 1999, Yale researchers identified the protein which is responsible for removing the nipples in male mice. In male mice, PTHrP signals the mammary cells to form male hormone receptors, which destroy the tittie and leave male rodents nipple-free. Male humans, however, undergo a similar embryonic process but without the mammary tissue breakdown. After three to four weeks, all embryos develop parallel mammary ridges known as milk lines before 23rd chromosomes, XX or XY, adapt the sexual dimorphisms. As the foetus grows, these milk lines extend to the top of the chest and the lower abdomen recede and just leave a pair of nipples behind, along with the milk-producing glands known as lobules, ducts and the fatty tissue in between. Without a protein such as PTHrP stepping into action to trigger the hormonal roadblocks like it does within certain rodents and mammals, human embryos are built the same way in the breast region.
The best explanation for men having nipples is that all embryos, irrespective of gender, start out with them and evolution hasn’t gone far enough yet to remove them off our male counterparts. Because nipples and healthy breast development are so closely linked with female success in the reproductive department, it’s believed by evolutionary biologists that the adaptive pressure to wean out male nipples simply wasn’t strong enough. Because male nipples don’t really have a purpose beyond the decorative, to put them in the same category as the appendix, wisdom teeth and other useless anatomy would be a technical mistake.
After all, men’s nipples can’t be relegated to the evolutionary rubbish bin if they can produce milk, which they can! While it may seem absurd, it’s not as far-fetched as it may seem – the hormone prolactin, which facilitates breast milk production, can pass through the placenta into an infant’s body, and after birth that in utero prolactin can cause a newborn to spontaneously lactate regardless of whether it’s a boy or a girl, as both genders have the same breast anatomy during the foetal development stage. This phenomenon is known as witch’s milk and often stops after a few weeks. Evolutionary biologists have long wondered why nipples have remained on the male body for so long given they minimal purpose. Some consider them to be a leftover and, as such, one of the useless parts of the body. The future, highly evolved man could be nipple-free, along with wisdom teeth and the appendix being thrown in the body part bin. After all, in terms of evolution, we’re still only babies – the human race has a long way to go, having only been on the planet a short while in comparison to some other species. Only time will tell if the men of future generations develop in this way.
