In a Nutshell : Men have nipples because women do.
At guernseyDonkey.com we’re always keen to try to add to that great body of knowledge that we like to call “Internet Fluff”. So for our latest contribution let’s consider “Why do men have nipples ?”
The importance of nipples to women is obvious: they deliver milk to suckling babies – up to 900 ml (1.58 pints) a day! Other mammals manage even more impressive feats of lactation. In 2010 a cow from Wisconsin was recorded as producing a stagering 175.98 pints (over 100 litres) of milk a day for a year! (Cows normally manage around 31 litres a day (54.55 pints).
However, nipples appear to serve no purpose at all in men. Having nipples is part of what defines a mammal (mammals are animals that suckle their young, for which they need nipples), but not all male mammals have nipples. Stallions (male horses) don’t have nipples, and neither do male rats or mice.
So men probably have nipples because there isn’t a good enough reason for them not to. When embryos are developing in the womb they start off fairly unisex – both male and female embryos begin developing all the same body structures, and these include nipples, which appear around the 4th week of development, by the 7th week, the baby’s body begins to assume one gender or another as the sex hormones kick in, causing male babies to develop their sex organs, with the vaginal labia fusing to form the scrotum and the clitoris developing into the penis.
Nipples are not sex-linked body features in the same way as the genitals, so no signals arrive to cause the developing male embryo to lose them
Nipples are not sex-linked body features in the same way as the genitals, so no signals arrive to cause the developing male embryo to lose them. If having nipples were a significant cause of problems for men, or in any way affected their survival and chances of having babies, there would have been pressure via natural selection for them to be lost. But this obviously hasn’t been the case, so there has been no reason for men to evolve some special mechanism to lose their nipples during the development of the embryo.