why do guys have nipples?

Answer 1

Evolutionary biologists, whose job it is to explain variety in nature, are often expected to provide adaptive explanations for such "why" questions. Some traits may prove—through appropriate tests—to be best explained as adaptations; others have perfectly good evolutionary, but nonadaptive, explanations. This is because evolution is a process constrained by many factors including history, chance, and the mechanisms of heredity, which also explains why particular attributes of organisms are not as they would be had they been "designed" from scratch. Nipples in male mammals illustrate a constrained evolutionary result.

A human baby inherits one copy of every gene from his or her father and one copy of every gene from his or her mother. Inherited traits of a boy should thus be a combination of traits from both his parents. Thus, from a genetic perspective, the question should be turned around: How can males and females ever diverge if genes from both parents are inherited? We know that consistent differences between males and females (so-called sexual dimorphisms) are common--examples include bird plumage coloration and size dimorphism in insects. The only way such differences can evolve is if the same trait (color, for example) in males and females has become "uncoupled" at the genetic level. This happens if a trait is influenced by different genes in males and females, if it is under control of genes located on sex chromosomes, or if gene expression has evolved to be dependent on context (whether genes find themselves within a male or a female genome). The idea of the shared genetic basis of two traits (in this case in males and females) is known as a genetic correlation, and it is a quantity routinely measured by evolutionary geneticists. The evolutionary default is for males and females to share characters through genetic correlations.


The uncoupling of male and female traits occurs if there is selection for it: if the trait is important to the reproductive success of both males and females but the best or "optimal" trait is different for a male and a female. We would not expect such an uncoupling if the attribute is important in both sexes and the "optimal" value is similar in both sexes, nor would we expect uncoupling to evolve if the attribute is important to one sex but unimportant in the other. The latter is the case for nipples. Their advantage in females, in terms of reproductive success, is clear. But because the genetic "default" is for males and females to share characters, the presence of nipples in males is probably best explained as a genetic correlation that persists through lack of selection against them, rather than selection for them. Interestingly, though, it could be argued that the occurrence of problems associated with the male nipple, such as carcinoma, constitutes contemporary selection against them. In a sense, male nipples are analogous to vestigial structures such as the remnants of useless pelvic bones in whales: if they did much harm, they would have disappeared.

Answer 2

All fetuses start out female and stay female until the point in a pregnancy when the female and male genitalia are formed.

There's a book called "Why do men have nipples?" that explains this.

Answer 3

The conventional science response will be that it is a byproduct of the fact that females need them. But while possible, it is a hypothesis needing to be tested. One possible reason for guys with nipples concerns sexual selection and sexual signalling. Females might like guys with visible ones, not necessarily for any particular reason except that their brains react to them, and thus guys with salient nipples tend to get mates more easily. No particular evidence for this that I know of, but neither is there for the byproduct explanation.

Answer 4

Because females need them.

An essay by Stephen J Gould called "Male Nipples and Clitoral Ripples", published (certainly in the UK) in a book called "Bully for Brontosaurus" in 1991 explains it all rather well

Answer 5

Yes they do and there are milk ducts behind them to just takes a lot of work to get them to Produce any thing

Answer 6

Hi. Because there is no survival benefit to NOT having them. The DNA that codes for them is shared by all humans.

Answer 7

its only a vestige. i think there is no important function for it except for gays who want to suck other man's nipples

Answer 8

Same reason that girls do, just a guy's doesn't produce milk.

Answer 9

View my best answers.


thanks for the question.

Answer 10

bkzalley copied and pasted that material right ;)