Butt hair

Factual Questions
21

Humans grow wiry hairs in their genital region, why we’re not quite sure. We are one of the only animals to naturally grow profuse hair on the skin around our genitals and anuses - most species have less hair there than elsewhere, for cleanliness I would assume. Other species also do not grow thick long hair around their mouths. What a mess.

Men grow more pubic hair than women on average due to hormones. Unlike many animals our asshole is right next to our genitals - although just how close also depends on individual hormones.It’s mostly just overgrowth, but I imagine it’s worse the shorter your taint is, if you’re a guy.

It’s worth noting that lots of humans - a large majority of the population, I would say - don’t naturally grow much or any hair on their butt, in the crack, or around the anus. Or much hair on their face. That throws any arguments about the empirical usefulness of beards and butt hair out the window IMO. It’s mostly a Caucasoid guy thing. Yall are kind of gross.

22

Does everyone in the world get dingleberries, or is it the result of the way we westerners sit down to poo? The rest of the world squats, which is actually much healthier. Do they have less asshair problems?

I just create my own.

23

No.
No, maybe.
Depends on which rest of the world.

24

That’s what fitness means in evolutionary context. Fitness (biology) - Wikipedia

Really, I’m not saying anything controversial. Just stating very basic evolution principles.

25

I shave all that off. It’s way easier to get peanut butter off a linoleum floor than shag carpeting.

26

This statement is wrong. It’s wrong because evolutionary advantage is not a zero-sum game.

27

Beat me to it. Glad someone else whiles away their time on bestof craigslist from time to time.

28

Zero-sum game between whom? I cannot make any sense out of that objection.

29

Evolution is a not like accounting where resources have to be measured against a finite balance sheet.

Nor should there be the expectation of evolution leading to ever greater optimization or efficiency.

30

Yes, there is an expectation that evolution will lead towards increase in efficiency / fitness. That’s actually exactly what evolution does.

I’m not really sure how to continue this discussion. I work at the university as a geneticist. Based on what you are writing in this thread, it seems that you haven’t read much about evolution. That’s okay of course, but I’m just confused about why you are speaking about it with such authority.

31

Maybe it could convince you that Cecil has written about a similar subject:
http://www.straightdope.com/columns/read/919/what-is-the-purpose-of-the-hymen

32

How can you be a geneticist and say things like, “Growing hair has a cost. If there is no advantage to it at all, people with hair would pay that cost, while people without wouldn’t” as an argument that hair must therefore have created an advantage in a given population?

Evolution is not progress; it is not a drive to improved efficiency. Evolution does not have a plan; it is not guided. Evolution is “any change in the frequency of alleles within a gene pool from one generation to the next,” to quote a standard Biology textbook definition. Or, to quote from “Introduction to Evolutionary Biology” by Chris Colby: “The process of evolution can be summarized in three sentences: Genes mutate. Individuals are selected. Populations evolve.” Quoting Colby again, “Evolution is not progress. Populations simply adapt to their current surroundings. They do not necessarily become better in any absolute sense over time.”

Given time, it is true that populations that survive in a specific environment will be overall better adapted to survive in that specific environment, but that does not mean there won’t be a legacy of “inefficient” traits (accepting for now the notion that any trait that does not enhance an organism’s reproductive opportunity is inefficient), nor can one necessarily expect those traits to vanish. In fact, one should expect many traits that lack the potential for reproductive advantage to persist, simply because parent generations had them and they were not removed from the population via natural selection.

I’ll quote Colby one last time since he explains it so well: “Natural selection may not lead a population to have the optimal set of traits. In any population, there would be a certain combination of possible alleles that would produce the optimal set of traits (the global optimum); but there are other sets of alleles that would yield a population almost as adapted (local optima). Transition from a local optimum to the global optimum may be hindered or forbidden because the population would have to pass through less adaptive states to make the transition. Natural selection only works to bring populations to the nearest optimal point.”

33

Ok, now you are putting arguments behind your statements, which is good. And I mostly agree with the things you say here. This last statement leads to the obvious question is: Why wouldn’t they be removed via natural selection? You quoted yourself that “Individuals are selected.” If individuals with a trait are selected against, even just by a small factor, we would expect the trait to decrease in frequency in the population.

Also, I am in no place making the mistake of thinking that evolution has a plan or is guided.

This is also correct, but not really relevant in our case. You don’t have to go a very complicated route from having butt hair to not having butt hair.

34

Sure, but I think your threshold for “small factor” is incorrect. Lots of “inefficient” traits do persist in nature because “cost” is not a zero-sum game. A useless, gigantic extra leg on a person would be a very large cost and probably selected against; something like finger bones in a whale fin is below the threshold and persists. Butt hair could be an example of the latter. Human’s ancestors at some point in the distant past had full body hair. Now, that hair is mostly very fine and thin, and thick hair is pushed to limited places on our bodies. At some point in the distant past, full body hair undoubtedly had some reproductive advantage in species which were our ancestors, but the near elimination of hair in homo sapiens was selected for. The remnant of our body hair is possibly just the obsolete legacy of species which were our ancestors, and homo sapiens butt hair itself may not have served to provide any reproductive advantage for many thousands of generations, and I would not expect it to be selected against anytime soon, especially since we have no problem just shaving (or waxing) it off.

I’m not sure that’s true. Not being a geneticist myself, what other genetic traits is butt hair close to or associated with? In any case, “complicated route” is not the issue, passing “through less adaptive states to make the transition” is. I do not know whether that would be the case for butt hair, but it might be.

However, the main point, the reason why I quoted that passage, is “Natural selection only works to bring populations to the nearest optimal point,” i.e. not maximized efficiency or “fitness.” In other words, all an organism has to do is survive, not survive spectacularly or even efficiently.

35

I always thought the answer seemed pretty straightforward. Is it just coincidence that we also have hair remaining in our armpits – another place that is likely to produce stronger scents than the rest of the body? Having hair in those places allows for more pronounced odors in that part of the body, a legacy from those days when it might be useful (and more socially acceptable) to go around sniffing those places in others.

I thought that was established. Perhaps I was wrong.

36

Wouldn’t surviving more efficiently allow for the production of more offspring? Reproduction requires a sacrifice in energy, after all.

37

Why? How small does a factor have to be not to matter? Or in other words, what is the smallest decrease in fitness a trait can cause for it not to be selected against.

The transition stage (if there even is one) for this trait is quite certainly just “less butthair”. So this particular argument isn’t valid in this case.

38

Fine one to talk. Sarah being Sarah, if she had ever had a dingleberry incident she’d surely have worked it into a routine by now.

39

That Koehler bidet is so silvery and slick, and has glimpses of a man shooting his cuffs, getting ready for something really cool, I suppose, ready to hop in his Aston Martin. Placed in the same room as a Sub-Zero refrigerator, it would match perfectly.

I never thought about James Bond having dingleberries and swampish genitals before. Now I have, and it’s a slight drag. :frowning:

40

This is outside my expertise. But it does seem that some traits are not (or are no longer) linked to reproductive success, but are potentially retained for many thousands of generations or more, traits such as the finger bones in a whale fin, blue eye color, freckles, and, yes, butt hair.

For a trait to disappear, there must be selective pressure against the trait. It seems to me that butt hair does not have any selective pressure against it, unless it is linked to some other trait that is being selected against. I’m not sure what that would be.

Do you know this for a fact? You’re the geneticist, not me.

Again, this is getting outside my personal knowledge. But what if the elimination of the gene that includes butt hair as a secondary trait was linked to a trait which includes maturation of gonads, for example? Or you could speculate on something else linked to the butt hair gene that is less drastic, but still maybe disadvantageous. Butt hair is linked to all secondary hair growth, including pubic hair, arm pit hair, beards, chest hair, and so on. At least some of those traits have been considered sexually desirable in some human populations. Probably not butt-crack hair. But in any case, most mature sexual development traits are linked in some way, so it seems likely that butt hair, for all its unsightly and dingleberry drawbacks, is not easily unlinked from the genome at all, just as the link I quoted above explains. “Transition from a local optimum to the global optimum may be hindered or forbidden because the population would have to pass through less adaptive states to make the transition.”

Clearly, what we really need in this thread is a specialist in the human genome, specifically on the topic of androgenic hair, to answer the question about whether butt hair is linked to traits more necessary for human reproduction or not.

Any butt hair scientists in the house?

But this also doesn’t link butt hair to anything like a “purpose,” per se. I mean, really, the best answer I’m aware of to the question “What is the reason we have butt hair?” is little more than “Because our ancestors had it, and it has not been selected against for many thousands of generations.”