My male nipple paradox

The male nipple leads me to believe something which I reject.

It seems that single-sex mammals must have existed before they split into male and female.

If sexual reproduction preceded the development of mammals, why would males have nipples?

I’m a database designer. We have salespeople and production people using the same system.

When I write a function strictly for use by the production people, there’s a button for invoking that function available on the menu screen that salespeople and production people both use. If a salesperson clicks on the button, they get a message saying that they don’t have the proper privileges to invoke that function. Nevertheless, the function exists, as does the button that invokes it, and it could be turned on for them if needs or situations change.

It’s just efficient development to do it that way.

If some anal-constipated managerial type insisted that I “disappear” the buttons of non-salesperson functions from the screen when salesfolks log in, I could do that, but it’s more work for me, not less, to customize the interface and make the buttons actually not be present for users for whom their functionality is disabled.

It has to do with the way mammals develop. So far as I know, all critters start out female, and if they have the requisite chromosome they turn male instead. Vestigial nipples are merely a sign of this.

Of course, there are also some species in which the males lactate (some sort of fruit bat, I believe) and it’s possible to get male humans to lactate if you feed them the right hormones. So the male nipple isn’t entirely a dud.


Cecil’s Why do men have nipples?

Some of the zillion previous threads:

You’re making an assumption here that just because you have a feature, it must be needed or useful. In natural selection, however, the converse is true; you develop organs and features that are useful, but those that no longer serve a function are not automatically eliminated by some kind of editing process. It merely reduces their demand on the organism to the point that they are not a hinderance to successful reproduction.

In the case of the nipple, (which occurs in all mammals of both sexes) it exists as a developmental feature of the human fetus; it is stimulated to develop by the release of hormones; it is more simple, in terms of development, to use the same anatomic “template” for both male and female, including non-functional vestigaes or alternatively functional organs, modified sufficiently to accomodate the differing biological roles of the sire and mother. Indeed, male human nipples are not truly vestigal, as they can be stimulated, via the proper hormones, to produce milk (as does sometimes happen during the turbulent hurricane of hormones in puberty, and during some hormone-affective medical treatments) and there is at least one species of mammal (the Dayak fruit bat of Malaysia) in which the male is responsible for providing milk to the young.

Sexual organs, the most blantant differentiation between male and female in any mammalian species, are clearly of similar origin but differ in development. The paraurethral glands (located in the urethral sponge) for instance are the female equivilent to the male prostate; similarities can be seen between the clitoris and penis, overies and testes, et cetera. Indeed, in embryonic development, many vestigal forms and phenotypes are seen which develop incompletely and then disappear, or are formed into an organ of an entirely different function. You can, for instance, thank the ancestors of lampreys and early reptiles for the hammer, anvil, and stirrup (properly, the malleus, incus, and stapes, collectively known as the ossicles), which are derived from (in the first case) the gill supports of jawless fish, and the latter from the jaw bones of early reptiles. Other examples of vestigal or transitional characteristics are apparent in even a cursory examination of anatomy, including the veriform appendix, the coccyx (tailbone), et cetera.

Oh, and the old wives’ tale about Man having one less rib than Woman has been addressed by the Master.

So, the reason men have nipples is the same reason that the VW Jetta has the same chassis as the Audi A4; 'cause it’s just cheaper and easier to build them the same and then stick a different emblem on them.


I got it.

The program (DNA) is written for “human being”, not ‘male’ or ‘female.’

Maybe that makes homologous structures inevitable and absolute.

Have you got a cite for that? I like bats, and have read plenty of bat books and sites and don’t remember hearing about this. Considering how often the properties of bat spermatozoa are mentioned (in some species, impregnation occurs months after mating), I think that they’d say something about lactating males.

Well, that’s a grotesquely oversimplified version. That throwaway line from *Jurassic Park * was sort of correct (and admittedly, it amazed me that kind of knew that) but they so overgeneralized about it.