Why do men have nipples?

[SacrificialSoldier]

Man Milk (Y)

you can be the first to test it.

[TheElite]

Because we're related to primates through a common ancestor.

You maybe, yeah.

[vincent]

You maybe, yeah.

Do you really want to go there with me again?

[davemania]

Like all "why" queries, the question of why men have nipples can be addressed on many levels. My four-year-old daughter, always suspicious of a trick when asked such obvious questions, answered: "because they grow them." In search of the trick answer, she quickly added that "chests would also look pretty funny with just hair."

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.

In a now-famous paper, Stephen Jay Gould and Richard C. Lewontin emphasize that we should not immediately assume that every trait has an adaptive explanation. Just as the spandrels of St. Mark's domed cathedral in Venice are simply an architectural consequence of the meeting of a vaulted ceiling with its supporting pillars, the presence of nipples in male mammals is a genetic architectural by-product of nipples in females. So, why do men have nipples? Because females do.

Similar to the evolution aspect already mentioned.

http://www.sciam.com/askexpert_question.cf...mp;chanID=sa008

[The_Decryptor Veteran]

Do you really want to go there with me again?

Dude, he just called you a primate.

Which makes sense considering we are related to them (I'd even go so far as to say we are one of them).

Honestly, it does make sense though, they have nipples, we have nipples.

And we have Man Milk??

[revvo]

We all evolved by starting out as girls. The male junk and bawls came up after. I'm not saying we're shemales or whatnot but that's how we become a male baby, the penis wasn't there from the beginning!

[andresjk]

the body has bugs as software does

[TheElite]

Do you really want to go there with me again?

Where? To the zoo?

[Jason S. Global Moderator]

b/c we're all the same genetics. men still have vaginas and women still have what could be considered a penis. women have breasts and men have man boobs... well some do. we all have nipples.

[Rob2687]

So we can still do this...

:p

[Nicholas-c Veteran]

nipples are purely genetic when u are first made (sperm and egg meet) the X chromosome is the only one active and does everything until a certain point and then it asks the "second" chromosome what to do if this is X then it produces and grows features of a girl and Y would make the body grow the male parts.

im surprised i remember this over a year ago i needed it at school :p

[Cailin]

No, we do not start out as females. We start out as either female or male as our chromosomes dictate, but have a weird female "template" thing going on.

You are mostly right here. There certainly aren't defined genitals before many weeks past conception. What happens, normally, is that the gonads, with presence of a second X chromosome, become ovaries; with a Y chromosome, they descend and become testes. Men have a scar between their legs where the skin from the "vagina" fused together after the testes descended.

The simple answer to the question at hand is that if a male takes estrogen, they will grow breasts, as the "plumbing" is available to be used there, but there is just no use for it. Males can only lactate if they have milk ducts, which I don't know are available without estrogen or not. Women's breasts are larger simply because they can store enough milk to feed their child.

There is a condition where a male fetus doesn't react to the male hormones for some reason and it just follows a female template. I can't remember if the baby will have ovaries/womb though...I don't know if this requires two x chromosomes - but it will grow up as a girl until someone does a DNA test...

Could probably do it using hormones, because it's hormones that give women this ability as far as I can tell.

This condition is called Androgen Insensitivity Syndrome. The male child, in the womb, does not react to testosterone, because of a lack of receptor cells available. The child ends up developing as a female, of varying degrees. The most severe form of this syndrome is known as Complete Androgen Insensitivity Syndrome, where the child will end up looking like any other female at birth; this most extreme form is usually only discovered at puberty (their body won't produce much estrogen on their own).

[NikkiRox]

i can't be bothered reading the thread, but from what i know, everyones a "female" until the genitals grow. or something like that.

[Hum]

Thank goodness I have nipples -- they feel oh sooo .... good. :p

[qdave]

^i hope they are milky :p yumm!