Why do men have nipples?

Cecil's Columns/Staff Reports
1

The reason this question was asked is because of a misunderstanding of evolution. Evolution does not get rid of “useless” attributes. It only promotes useful ones, where “useful” means “allows you to produce as many babies that survive as possible”.

For example, our brains have evolved because the smarter the cave-man the more likely he/she was able to:
[ul]
[li]have sex with many other cave-people[/li][li]have babies that didn’t get eaten[/li][li]protect themselves from the elements, disease, predators, etc.[/li][li]have babies that grow up to produce more babies[/li][/ul]

So intelligence is a useful attribute because it gives us the ability to do everything on the list.

But even something as cool as intelligence can be “useless” in an environment that does not require intelligence to produce babies that survive. It could be possible that the cave-people lived in a part of the world where one doesn’t have to worry about gathering food, getting killed, having plenty of mates, etc.

Evolution is all about babies. Once you’ve had a kid who’s had a kid, you’re usefulness is done… unless you’re trying to have another kid. The most successful species on earth are not us, it is insects. They have many, many babies and vast numbers survive.

But evolution depends on a certain amount of randomness to occur. So attributes will arise that aren’t immediately useful. But if the environment changes and those attributes become useful, then it was a good thing they came into being. For example, if it should happen that the ozone layer is eroded to a certain point, that men with certain kind of nipples allows them to have sex more often with more women and that their babies survive more often, then male nipples will be a successful evolutionary attribute and we shall hail them as sex organs.

Until then, men have nipples for no reason at all.

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Hello johna. Here is a link to the column in reference.

3

It is true that evolution does not get rid of useless traits. But it doesn’t stop them from going away, either: witness cave-fish, the blindness of which is not an evolutionary advantage (since they expend the energy to grow the eyes anyway, they just can’t see through them.)

But men have nipple for the exact reason Cecil said : it’s a non-sex-specific trait. How can this hav evolved? If nipples happened to evolve as a non-sex-specific trait, then it would help the females and not hurt the males much. So since it is a net advantage they stay, since the alternative would be that no one gets nipples.

The second alternative is to evolve the nipple a second time in a sex-specific way, which just hasn’t happened to happen, and we already have perfectly servicable nipples anyway so it would not be an advantage to evolve them.

4

Right. If blindness doesn’t prevent them from having babies, then the trait sticks around. It’s the having babies part that’s important. They can be dumber than a doornail, blinder than a bat, and deaf as a post, but if their package works and they can have kids, the species survives.

The implied question was “is there a hidden reason or a long past reason for male nipples?” The answer is no, there’s no such reason for male nipples.

The answer to the literal question “why do men have nipples” is that we all start off as proto-humans that are not sex-differentiated. A squirt of testosterone makes a male, a squirt of estrogen makes a female. The female gets the lactating breasts, the male does not. (sorry I don’t know the correct term for “proto-human”, maybe “fetus”, “zygote”, don’t know?).

The most likely reason the proto-humans start off with breasts is that it requires less energy in the overall system. Generally speaking if there are two paths for something to take, it will take the one that requires less energy (a sort of a twist to Occam’s Razor). It takes less energy to have the proto-human have nipples and one gets to lactate and the other doesn’t vs having the female grow a completely new appendage. By the way this also answers why we have two nipples, not just one.

But energy minimization is not really evolution as much as it is a fundamental principle in the universe. It is a driving factor in survival so there is a strong effect on evolution. Less energy, survives. More energy, dies off.

Life takes a lot of energy. If I stop breathing for only 4 minutes or so, I die. If I don’t drink for 3 or so days, I die. If I don’t eat for a couple of weeks, I die. Compare this to a rock. It remains a rock for millions of years. It expends very little energy to be rock.

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johna said:

I think Ludovic’s point is that the fish have non-functioning eyes. The eyes are still there and grow to some extent, but not to the extent to be functional. Evolution allowed the eye development to go away because the sight was no longer an advantage.

Perhaps, but this is a quirk from the early mammal development. The mammary development is not sex-differentiated, whereas testes vs. ovaries is sex differentiated.

No it doesn’t. Bilateral symmetry answers why we have two nipples not one. What explains why we have 2 nipples instead of 8? Because they actually develop and then undevelop. You would think energy-wise it would be better to skip the formation on those other sets of nipples that are going away eventually, no?

6

I agree with you, but I wouldn’t use your characterization of “Evolution allowed…”, evolution itself doesn’t do anything because there is no such concrete thing.

And the eye development didn’t really “go away” either. The blind fish were able to propagate without sight and so it didn’t matter if the fish got blinder or not. If by chance, there was a fish with more vision, it would survive as well as the others. But blindness in the gene pool will eventually overrun any minority groups with vision. So the entire population becomes and stays blind.

On the other hand, a minority group will splinter off or overrun the overall population only if there is a significant advantage from it’s traits to allow it have offspring that survive with that trait.

The parts that are sex-differentiated must be differentiated to propagate the species therefore it is worth the while to spend the energy to differentiate between the male and female.

In any case, perhaps I’m wrong but nipples are sex differentiated. My nipples don’t lactate, a woman’s does.

Bilateral symmetry is a result of minimization of energy. It’s a simple mechanism that requires less energy comparatively speaking to allow an organism to grow from a original single cell.

Not sure what you mean by “develop and then undevelop”?

7

Not really. Most women’s nipples don’t lactate most of the time. Some women’s nipples never lactate. Yet they remain women.

Also, years ago I believe that I read that some men can lactate small amounts. I have no idea if there is any truth to that.

Volunteers?

8

Easy question. Men have nipples to intimidate prospective sons-in-law.

9

**johna ** said:

You’re harping over a turn of phrase rather than a semantic content difference.

Begging the question. There was a time before sex differentiation that propogation of the species occurred. It just wasn’t the human species at the time.

But you seem to have missed my point. Nipples (and in fact breast tissue) are developmentally hardwired in the basic body plan. Hormones trigger sexual differences in development. Hormones driven by the X and Y chromosomes are what make parts different. Nipples are not formed by a sex-driven hormone change.

Lactation is caused by the breast tissue, not the nipples. It is hormonally induced. Men have lactated due to hormone imbalances.

From the column:

Human fetuses start to grow up to seven pair of nipples, but only 1 pair fully develop. The rest typically go away, though occassionally there are vestiges.

10

Harping. Interesting.

I think in this case it does pay to be more precise in wording since Evolution and religion are associated, albeit politically and negatively.

Evolution is not an active entity doing or striving to do anything. It isn’t even passive either, because there is no “it”. There is no hidden hand, no all seeing eye, no entity, visible or invisible. There are side-effects of the existence of random variants in a species and the dying off of offspring vs the survival of offspring specifically so they can propagate… or not. The convenient name attached to all that is “evolution”.

My “semantic content” is this: it’s incredibly easy to anthropomorphize evolution and my fear is it becomes a pseudonym for “god”. Some examples of people’s tendency to do this: the new-agers have appropriated “the universe”, of which you can ask for things to be given to you, i.e. just like God. And then there was the “tao of physics”. And the application of Heisenberg’s Uncertainty Principle to nearly everything under the sun, etc, etc. So what’s next, Evolution as another of God’s plans taught in a creationist curriculum? That may sound outlandish, but then again so is Mature Creationism.

As an aside, I don’t think the ever popular “survival of the fittest” is an accurate phrase either. Can’t you just smell the elitist machismo emanating from it when the alpha male pronounces it? At worst it’s just a thin veneer over top of eugenics.

You don’t have to be the “fittest” to survive. In fact, I believe if it is survival of only the fittest, evolution wouldn’t work as robustly as it does, i.e. survival of some of the unfit actually helps the process and the species as a whole.

I see, thanks to you and Zoe for clarifying.

I got your point. What you’re saying is that all bodies in their basic form have nipples and since men derive from that basic form, they have nipples.

My point was at the next layer down in the causal tree: The basic body plan has nipples because the females do require them to assist in ensuring survival of offspring and it’s less expenditure of energy to not differentiate between males and females since there’s no advantage or disadvantage for males to have nipples.

Got it.

I’d say it’s a local minima. To cause the extra pair of nipples to go away requires changes to the structures in DNA, the proteome, etc. But that requires some expenditure of energy to change. There’s no significant survival advantage to eliminate them so they’re probably not going away any time soon.

11

Essentially, the genetic mutation which caused nipples/lactating to develop in the proto-mammal happened to express early enough in fetal development that it is not sex-differentiated. While there might be some minor energy saving in development of male fetuses to bypass nipple development, there must first be specific mutations to the controlling genes such as to change the start of nipple development until after sex differentiation begins, followed by another sex-linked mutation to turn off “nipple” genes in males only, followed by a strong enough good/bad effect on the individual that natural selection has something to work on through preferential survival and reprodution success of nipple-less men.

Until this happens, men will continue to have nipples because that’s the way the relevant genetic mutations happened to occur.

12

Note as well that that it is easier to suppress the multiple pairs of nipples down to a single pair because this sort of duplication is generally a matter of having the"grow nipples" gene matched to a “how many times to do it” gene which is fairly easily modified to reduce or increase the number of whatevers actually develop. (This is also why some babies are born with six fingers - the “grow a finger” gene was turned off one finger too late.)

All of the above is much simplified, of course.

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johna said:

I understand all that. I’m a raging Evolutionist myself. Perhaps not as bad as PZ Myers.

Fair enough. That wasn’t my intent. Humans have a tendency to speak in cause and effect, and treat the “cause” as an entity, even if it is a non-directed process.

Trust me, I’m against that other crap as much as you. I hate the “religious metaphors” applied to science. It cheapens both.

It’s not so much the expenditure of energy that’s important, but rather the outcome of where in the process of fetal development the trait appears. It is certainly plausible that during the mammalian development process nipple/breast formation could have occurred later in the process. It is possible that hormonal changes driven by the sex chromosomes could have then altered the breast tissue during fetal development, rather than puberty. That just isn’t how it worked out.

But I think I understand what you’re saying, and we’re not quite talking on the same level. Fair enough.

Also, what Bookkeeper said.

14

On a particularly nauseating episode of “Enterprise”, our “heroes” gleefully commit genocide, secure in the thought that they’re working the will of the great evolutionary ju-ju. The idea’s been common as muck among brain-damaged intellectuals for as long as evolution’s been on the table. (Actually, in fact, it was in the air a little earlier than evolution was, perhaps as a reaction to the growth of Deism in the 18th-century. See Blake.)

15

Could you remind me of that episode? I don’t remember it offhand. Not that I’m doubting you, I just don’t remember it.

16

I assume you mean animal species since among all life the most populous species are bacteria and this will always be the case as larger species basically rely on them for their existence.

The idea that insects are “more successful” than us is a common factoid with no clear meaning. There are lots of things we might mean by most successful and highest frequency of individual organisms is just one of them. Mother Nature makes no value judgements so it’s up to us whether most individuals trumps most biomass or species longevity or fastest rubik’s cube solving (I think humans will have this title for some time).

Similarly I dispute the factoid “The meaning of life is to reproduce” but I won’t elaborate unless prompted.

17

You can still be an evolutionary factor even if you can’t have any more offspring. Also “insects” is not a species.

18

Not sure what you mean.

If you neutered a bull, how could it influence the genetics of the species?

Do you mean predators?

Ok.

My point is lots of offspring makes the evolutionary process more successful in producing variants which survive environmental changes. Some kinds of insects produce vast numbers of offspring and seem to be surviving over a very long time.

19

w.r.t. “insects is not a species”.
I thought johna was using species in the plural form, hence I did a similar thing in describing bacteria species.
But looking again I see his grammar has given him away :slight_smile:

Ah. But I doubt that insects are the most “successful” under this definition.
For example, a female cod may produce 6 million eggs. OK, so not all of those will get fertilised. But nonetheless, in terms of animal species that produces the most offspring, the answer must be an aquatic species (can’t seem to find a definitive answer).

20

Not all eggs get fertilized? Simple, produce more eggs! Many babies => increased odds of at least some of them surviving.

Simple logic, simple math, easy as pie. Gotta love evolution for getting the job done and for it’s underlying elegance and pure simplicity in the face of a very messy reality! Occam’s razor at it’s best.