What's this for, love?

June 5, 2007 2:35 PM

Useless body parts. Nearly a century and a quarter after Darwin’s death, science still can’t offer a full explanation for why one outdated anatomic trait lingers in the gene pool and another goes. Modern genomics research has revealed that our DNA carries broken genes for things that seem as though they might be useful, like odor receptors for a bloodhound’s sense of smell or enzymes that once enabled us to make our own vitamin C. In a few million years, humans may very well have shed a few more odd features. So look now before they’re gone.
posted by psmealey (113 comments total)

Article from 2004, but body parts remain useless today
posted by psmealey at 2:35 PM on June 5, 2007 [11 favorites]

science still can’t offer a full explanation for why one outdated anatomic trait lingers in the gene pool and another goes

The article is interesting, but this statement is poppycock. Science can definitely offer a full explanation for vestigial traits and whether they stay or go.

Now, it could be that scientists can't offer a full explanation on the reason for a particular trait staying or going (because they haven't figured it out yet), but the evolutionary theory about this is extremely well thought out.
posted by mcstayinskool at 2:41 PM on June 5, 2007 [6 favorites]

Ahh, excellent timing. I asked about useless stuff in the askmefi thread about ever-growing human hair.
posted by notyou at 2:43 PM on June 5, 2007

What about that floating bone in the middle of our necks? That always struck me as something that should evolve away.
posted by Ambrosia Voyeur at 2:50 PM on June 5, 2007

I know that hiccuping is tied to the swallowing reflex. Because many of our genes are used two or three times for different purposes, nature won't bother to tease out hiccuping from swallowing. The swallowing reflex is vital to nursing, and hiccuping just isn't that bad. The hair on the toes is probably part of a larger pattern of hair distribution. These variables just aren't that independent.

On the other hand, you'd think it would be very useful to turn on a vitamin C pathway. Still, not all that necessary, not until Waterworld comes to pass.

Nature's criteria seems to be "if it won't kill you before you pump out two to four kids, we leave it."

I think we should just turn on all of these nifty, neglected metabolic pathways and see what fun we get. Hell, let's just cull all of the introns, like they did in those mice, and check out our mutant offspring.
posted by adipocere at 2:55 PM on June 5, 2007

Things do not evolve away!!!!

Evolution is a process that is blind to design.

If a disease were to strike to world tommorow and the only ones immune were those with sickle cell anemia, evolution would not have chosen to make the human race dark skinned with curly hair...but that would be the result.

reproduction is the only goal of evolution. DNA that is inside organisms that reproduce more, has more chance of existing.
posted by Megafly at 2:56 PM on June 5, 2007

If a genetic trait doesn't affect your chances of producing viable offspring, there is no selective pressure for or against it, and the incidence of the allele is likely to remain unchanged across generations. That's how I remember it from the anthro I took.
posted by autodidact at 3:00 PM on June 5, 2007

Useless body parts.

Useless? Really? I've got a shipping container full of these things, what the hell am I going to do with them now?
posted by quin at 3:02 PM on June 5, 2007 [4 favorites]

That floating bone descended to allow speech. Now that it's out of the way, there's no reason for it NOT to stay. Eventually, genetic mutations will appear that remove it, much like those who are already missing some of the parts listed above, but since it's not selected for or against at this point, and since having a hyoid bone versus not having one does not, at least not yet, affect your chances of finding a mate and reproducing -- well, it's just gonna stick around as long as mutations allow.
posted by linux at 3:02 PM on June 5, 2007 [1 favorite]

God put all of those extra body parts and peculiarities there to test our faith. He's sneaky, that guy (gal?). Why do I have nipples? I don't know.
posted by chillmost at 3:05 PM on June 5, 2007

Around here the level of graffiti is really poor, people just scrawl messages, and there's no art to it. Worse, the political messages are neo-nazi (slurs against Jews, and interestingly, I have seen young blacks in the groups spraying and writing it), stylized swastikas, and calls to violence.
posted by nervousfritz at 3:06 PM on June 5, 2007

aw, heck, wrong thread! my fault. Sorry guys.
posted by nervousfritz at 3:06 PM on June 5, 2007

ISO SM, WE, NSA For sexy eugenics. No Hyoids.
posted by Ambrosia Voyeur at 3:10 PM on June 5, 2007

Are useless body parts an argument against intelligent design?
posted by chlorus at 3:10 PM on June 5, 2007

nervousfritz and his comments are useless.
posted by Brandon Blatcher at 3:10 PM on June 5, 2007

I dunno, that little toe is pretty good for finding furniture legs in the dark.
posted by Smedleyman at 3:14 PM on June 5, 2007 [11 favorites]

I use all of my body parts. All of them.
posted by The World Famous at 3:22 PM on June 5, 2007 [1 favorite]

I dunno, that little toe is pretty good for finding furniture legs in the dark.

Similarly the coccyx is pretty good at hurting like the dickens when you half fall down. "That's it, rub that coccyx baby... mmm... oh yeah."
posted by ob at 3:32 PM on June 5, 2007

Do you need any spares TWF?
posted by quin at 3:34 PM on June 5, 2007

We lost the Vitamin C synthesis only fairly recently. There are still some human populations with the ability to synthesize it.

Vit. C synthesis is a perfect example of the behavior of a vestigial trait, actually. We lost it because we were eating diets with plenty of vit. C in them already, so when people happened to have mutations that broke the pathway, they didn't die, and instead the allele spread through the population. More recently, we started taking long sea or desert voyages, and discovered that vitamin C synthesis was useful after all.
posted by hattifattener at 3:36 PM on June 5, 2007

science still can’t offer a full explanation

HA! WRONG AGAIN, SCIENCE!

Accept Jesus now.
posted by Krrrlson at 3:44 PM on June 5, 2007 [4 favorites]

If a genetic trait doesn't affect your chances of producing viable offspring, there is no selective pressure for or against it, and the incidence of the allele is likely to remain unchanged across generations.

In the long run, genetic drift and mutation may eliminate the allele. This is true even for alleles under purifying selection, although it is less likely for a sexually reproducing population with a large effective population size. Natural selection is not the only mechanism of evolution.
posted by grouse at 3:50 PM on June 5, 2007

hattifattener, are you sure about that Vitamin C synthesis in humans? IANAEvolutionaryBioligist, but I've always been under the impression that all humans require vitamin C in their diet, and a quick Google seems to confirm that. Maybe you're thinking of the recent appearance of lactose tolerance in human adult populations?
posted by Jakey at 3:53 PM on June 5, 2007

Wow. Now I'm wondering whether or not I'm in the minority population that has evolved away from the useless muscle groups etc. How do I know?
posted by nerdcore at 4:03 PM on June 5, 2007

In the long run, genetic drift and mutation may eliminate the allele...Natural selection is not the only mechanism of evolution.

I don't think any biologist today would dispute that last sentence; it's fairly obvious that other mechanisms exert selection pressure. However, the phenotypic effects of random mutation of the genotype is precisely what natural selection acts upon by definition, so that's a bit of a tautologous statement. Did you mean to say "...genetic drift and horizontal gene transfer may eliminate the allele..." or have I misunderstood you?
posted by inoculatedcities at 4:03 PM on June 5, 2007

I was just out camping and roasting a marshmallow over the fire and thinking to myself, "why can't animals break down cellulose? If we could break down cellulose then I wouldn't have to roast this marshmallow, I could just gnaw on a nice log and the forest could be my grocery store."

mmm. 100 year old Northern Red Oak.
posted by 517 at 4:05 PM on June 5, 2007

517- did you win a Nobel?
posted by Jakey at 4:09 PM on June 5, 2007

Do you need any spares TWF?

I'll take whatever you've got. Please send it to Old Pink, care of the funny farm, Chalfont.
posted by The World Famous at 4:14 PM on June 5, 2007

I'm unclear on how ear-wiggling is useless. It's fun to watch. I vote that we keep it.
posted by Tehanu at 4:17 PM on June 5, 2007

I don't think any biologist today would dispute that last sentence; it's fairly obvious that other mechanisms exert selection pressure.

Selection is not evolution. So these non-selection mechanisms of evolutions do not exert selective pressure, if that's what you mean, but they do affect evolution.

However, the phenotypic effects of random mutation of the genotype is precisely what natural selection acts upon by definition so that's a bit of a tautologous statement.

No, that is not the definition of natural selection. Mutation is not necessary for natural selection. Natural selection can act on systems in the absence of mutation.

Did you mean to say "...genetic drift and horizontal gene transfer may eliminate the allele..." or have I misunderstood you?

No, I did not mean to say anything about horizontal gene transfer.
posted by grouse at 4:17 PM on June 5, 2007

I'm unclear on how ear-wiggling is useless. It's fun to watch. I vote that we keep it.

Thanks to the magic of sexual selection you can exercise your right to vote! Mate with ear wigglers as much as possible to ensure the continuing existence of this trait.
posted by grouse at 4:21 PM on June 5, 2007

hattifattener, are you sure about that Vitamin C synthesis in humans? IANAEvolutionaryBioligist, but I've always been under the impression that all humans require vitamin C in their diet, and a quick Google seems to confirm that. Maybe you're thinking of the recent appearance of lactose tolerance in human adult populations?

hattifattener is correct. Many other mammals can and still do synthesize their own Vitamin C, though humans lost the trait due to an abundance of it in their diet. In particular, the mutations caused (almost all) humans to defectively synthesize lactonase (the important one) and L-gulonolactone oxidase enzymes--to be clear, the final synthesis is a non-enzymatic reaction, but effective versions of these vital enzymatic precursors are required. Those who who could still synthesize a tiny amount of Vitamin C on their own were the ones who survived all those transcontinental sea voyages we learned about in childhood. The rest died of scurvy, at least before Lind.
posted by inoculatedcities at 4:26 PM on June 5, 2007

*bets a shiny nickel that grouse can wiggle his ears*
posted by quin at 4:26 PM on June 5, 2007

I asked my allergy doctor what sinuses are for and what ultimate purpose they serve. Without missing a beat he said, "They put my kids through college."
posted by vronsky at 4:30 PM on June 5, 2007 [8 favorites]

Yeah, I hate this pop-evolution meme. It's not quite as bad as being naively teleological about evolution, but it's close. It's deeply related to teleology because it's thinking in terms of ideals—if that anatomical feature isn't useful, it's unneeded and thus, obviously, should "go away".

But evolution isn't things evolving toward a perfection, it's things evolving away from "not good enough". If you cross that "good enough" threshold, it doesn't matter if there are sub-optimal traits as measured against an ideal or if there are "useless" traits.

Finally, given how familiar we all are with legacy technologies and that irksome backwards compatibility requirement, it's very odd to me that people seem oblivious to the fact that evolution is extremely legacy bound. Getting rid of those male nipples might mean a complete alteration of a whole bunch of stuff that is important. What small negative selection there is against male nipples is overwhelmed by the greater negative selection of any mutation that turns the evolutionary clock back far enough to allow for the possibility of their non-existence. (That's really a metaphor, don't take that literally in any sense.)
posted by Ethereal Bligh at 4:31 PM on June 5, 2007 [1 favorite]

science still can’t offer a full explanation for why one outdated anatomic trait lingers in the gene pool and another goes.

WTF? It takes thousands of generations for traits to change. Some things we think are useless today are here because there hasn't been enough time for them to disappear completely. But that does not mean that they are not going away.


By the way, it is worth remembering that all evolution does is produce a set of possible alleles, but it is the environment that does the actual selection. And the environment usually takes a long time to change significantly (I mean on the global scale).
posted by c13 at 4:34 PM on June 5, 2007

“I asked my allergy doctor what sinuses are for and what ultimate purpose they serve.”

Well, even though this doesn't totally answer your question, we have moist surfaces at inhalation areas because it's much better to get infectious organisms there than deeper in the respiratory system.

However, if you're a fan of the very strong anthropic principle, then your doctor's answer is arguably correct.
posted by Ethereal Bligh at 4:37 PM on June 5, 2007 [1 favorite]

“But that does not mean that they are not going away.”

That doesn't mean they ever will, either.
posted by Ethereal Bligh at 4:38 PM on June 5, 2007

I have an extra cervical rib, and it's a pain in the neck.
posted by bwg at 4:39 PM on June 5, 2007 [3 favorites]

No, that is not the definition of natural selection. Mutation is not necessary for natural selection. Natural selection can act on systems in the absence of mutation.

You are correct; that isn't an adequate definition of natural selection, nor was I attempting to provide one, I was merely seeking clarification. I understand mutation is not always necessary for natural selection to occur but am I wrong to think that selection acting on the genetic substrate is the primary cause of disparities in fitness? Or is that way off the mark?
posted by inoculatedcities at 4:42 PM on June 5, 2007

Some of the things they mention are actually not useless at all. Palmaris Longus, absent in 10% of the population though it may be, serves to tighten the palmar aponeurosis when you're carrying a load in your hand, which actively prevents compression of veins in arteries in the hand. Absolutely essential for climbing and hanging from trees; still useful even if you're just carrying a shopping bag. And the characterisation of the VMO as playing no role in pheromone perception in human pheromone perception is not only premature, but ignores a lot of recent anatomical and physiological research.

(And Ambrosia: the bone in the middle of your neck, the Hyoid, acts as an anchor for the extrinsic muscles of the tongue. FUN FACT: It's also considered the most important bone in Japanese funerary customs.)
posted by Tiresias at 4:49 PM on June 5, 2007 [1 favorite]

As far as male nipples being useless I always thought that the purpose they served was to faintly amuse women...
posted by ob at 4:51 PM on June 5, 2007

That doesn't mean they ever will, either.

No, but I don't think we could tell either way.

I think the main problem that confuses people about evolution is time scale.

but am I wrong to think that selection acting on the genetic substrate is the primary cause of disparities in fitness?

Selection is a process, it can't possibly act on the genetic substrate. Certain things generate differences in DNA sequence, and the environmental conditions then select for the most optimal (or least deleterious, whichever the case may be) sequence. These are two different processes though.
posted by c13 at 4:52 PM on June 5, 2007

You'd think having three balls would be more a curse than a blessing, but it's not.
posted by bardic at 5:00 PM on June 5, 2007 [2 favorites]

I spent four years learning to wiggle my ears for nothing, it seems.

Wait a second, I get this magazine in the mail, how come I haven't read this yet...
posted by CitrusFreak12 at 5:03 PM on June 5, 2007

Wait, no, I have read this. There is no way I could have otherwise known all of these beforehand.

I want to know if I have the subclavius muscles or not. How can I find this out? Xrays? Can a trained physician feel around for them or something?
posted by CitrusFreak12 at 5:13 PM on June 5, 2007

Having fallen hard on my coccyx almost two weeks ago now and it still hurts like hell I'm voting to get rid of it. Could I have broken it? I suppose I would really know if I had done that.
posted by maxwelton at 5:29 PM on June 5, 2007

Answers here
posted by bicyclefish at 5:42 PM on June 5, 2007

Had Cole Porter made this FPP it's title would have been "What is this thing called, love?"
posted by sourwookie at 5:44 PM on June 5, 2007

Had Cole Porter made this FPP it's title would have been "What is this thing called, love?"

Bu-dum-crash!
posted by sourwookie at 5:45 PM on June 5, 2007

On a related subject:

Why in gods name does the human male's reproductive organs (actually I will refraise that) - why in gods name does the very sensitive human male's reproductive organs, dangle right out in front of the body, exposed to all the world's fast moving objects, knees and hands?

It doesn't make any sense to me...
posted by Samuel Farrow at 5:45 PM on June 5, 2007

I can say that definitely I spend a good deal of my life pretty happy that I don't smell more stuff than I do already. I think the 'bloodhound's sense of smell' has way more disadvantages.
posted by troybob at 5:46 PM on June 5, 2007

Aw, crap.
posted by sourwookie at 5:46 PM on June 5, 2007 [1 favorite]

Regarding the conversation about "natural selection is not the only mechanism of evolution" (grouse and inoculated cities), this was precisely the point made by the article in this recent MeFi post. The conversation in that thread ended up being about other things, but the point that is often missed is that this statement: "If a genetic trait doesn't affect your chances of producing viable offspring, there is no selective pressure for or against it, and the incidence of the allele is likely to remain unchanged across generations" is wrong, wrong, wrong. If a trait confers neither a disadvantage nor an advantage, then it will evolve by stochastic mechanisms such as genetic drift, rather than by natural selection. Things don't go away because they are not useful, but if they are not useful, they might or might not go away, depending on chance.

The main reason why seemingly useless things hang around, of course, is that the development of pretty much all of the different parts of us are controlled by the same few genes that are used over and over. It's hard to make a mutation that would get rid of one particular organ and leave all the others unscathed.
posted by nowonmai at 5:47 PM on June 5, 2007

Also, anybody who doesn't think male nipples serve a purpose is invited to come round here and have a gentle nibble on mine. You'll soon see how that could lead to a little perpetuation of the species.
posted by nowonmai at 5:50 PM on June 5, 2007 [2 favorites]

Why in gods name does the human male's reproductive organs (actually I will refraise that) - why in gods name does the very sensitive human male's reproductive organs, dangle right out in front of the body, exposed to all the world's fast moving objects, knees and hands?

Well, for one thing it is hard to stick something into something else if that something is on the inside of your body. As far as testicles go, they have to be kept at a slightly lower temperature (1-2 degrees) than the rest of the body, because higher temperatures are deleterious for spermatogenesis. So you have to keep them on the outside and use a pretty sophisticated countercurrent heat exchange system to keep them cool.
posted by c13 at 5:59 PM on June 5, 2007

why in gods name does the very sensitive human male's reproductive organs, dangle right out in front of the body, exposed to all the world's fast moving objects, knees and hands?

Quite simply, because it hasn't killed us yet.
posted by grouse at 6:00 PM on June 5, 2007

Why in gods name does the human male's reproductive organs (actually I will refraise that) - why in gods name does the very sensitive human male's reproductive organs, dangle right out in front of the body, exposed to all the world's fast moving objects, knees and hands?

Plo chops.
posted by nowonmai at 6:02 PM on June 5, 2007

Things don't go away because they are not usefu

They do, because if they are not useful, you're wasting precious energy synthesizing them. Energy that can be spent elsewhere. For example, bacteria spits out the plasmid if you forget to add antibiotic to the growth medium. Then you go through the whole protein prep and look like an ass.
posted by c13 at 6:06 PM on June 5, 2007

c13, I think Ethereal Bligh was trying to say that something useless does not necessarily mean that it will disappear from the genome immediately. In the example you give, the plasmid is not only useless, but highly deleterious because of its demands on the organism, and easily separable from other functional parts of the genome. Nonetheless, there is still an element of chance there, albeit a high chance per generation in the case of eliminating a nonfunctional plasmid from a bacterium.

In any case, the evolution of complex multicellular eukaryotes like humans is far less deterministic and slower than that of E. coli.
posted by grouse at 6:17 PM on June 5, 2007

Nipples are not vestigial. Males have them because fetuses don't develop sex characteristics immediately. By the time we do, the nipple has already begun to form.

As for having very sensitive sex organs exposed to the world: I have an unscientific theory. I'd rather have my achille's heal, my testes in full view, where I have a chance at protecting them in a fight, than tucked behind me like fourlegged mammals do. If I were an evolving male primate struggling for dominance, keeping my testes where I can see and defend them would be reason enough to learn to stand erect.
posted by gesamtkunstwerk at 6:27 PM on June 5, 2007

"if it won't kill you before you pump out two to four kids, we leave it."

I'd modify that to "... and successfully raise them to adulthood, plus perhaps help out with the grandkids...", since reproductive success only starts, and does not end with, the first generation.
posted by Heywood Mogroot at 6:33 PM on June 5, 2007

So do we still think that ~95% of genes are "useless"?












the sheer human conceit amazes me!
posted by krash2fast at 6:34 PM on June 5, 2007

Oh, I don't disagree with EB as far as "immediate" goes. Nothing about evolution can be described with this word. What I'm saying is that if something is not useful, it is most likely deleterious, simply because it puts and extra energetic load on an organism. "Deleterious" in this case does not necessarily mean "bad for the particular organism", but that it puts that particular organism at a relative disadvantage compared with others in that particular environment.

In case of the plasmid, it would get spit out even if it did not code for some useless protein. It would probably stay in longer, but eventually it would be gone.
posted by c13 at 6:35 PM on June 5, 2007

exposed to all the world's fast moving objects, knees and hands

somebody still needs to practice "Paint the Fence". . .
posted by Heywood Mogroot at 6:35 PM on June 5, 2007 [2 favorites]

So do we still think that ~95% of genes are "useless"?

That's a new one for me. But for many years the prevailing dogma was that the parts of the genome which were not in what were understood to be genes were "junk." This included the bulk of the genome. This is no longer the prevailing view.

the sheer human conceit amazes me!

Let's say you go to a library, pick a random book on the wall, open it to a random page, and all you see is "All work and no play makes Jack a dull boy." over and over and over again. The same sequence repeated endlessly, in up to 10% of the books you look in. That's what biologists found when looking at the human genome. Perhaps they could be forgiven for thinking that it was junk—it takes a lot of creativity to figure out what the point is.

if something is not useful, it is most likely deleterious, simply because it puts and extra energetic load on an organism.

I agree for a bacterial plasmid. Not for the sorts of human traits discussed in this article.

First, the genetic origin of these traits is complex. As far as I know, there's not some appendix gene that can be knocked out and suddenly humans won't have a useless appendix anymore. The appendix is a side-effect of a developmental program that produces a lot of useful stuff, and it's possible that Nature never has or never will produce a human without one.

But what if we took some sort of hypothetical non-functional human gene whose only effect was to produce some protein in cells that didn't really do anything? Considering what a tiny fraction of a human's total energy consumption that would take up, I'm not convinced that this would be detectable beyond the noise. And there are so many other traits that are far more advantageous or deleterious that I think it's unlikely that selection will have a chance to act on it.

If purifying selection isn't keeping it, it's still likely to disappear, but mainly due to mutation rather than selection.
posted by grouse at 7:07 PM on June 5, 2007

Then you go through the whole protein prep and look like an ass.

High school was rough like that.
posted by CitrusFreak12 at 7:13 PM on June 5, 2007

c13: a plasmid is not really a good comparison to a 'useless organ'. Bacteria have many genes that are not used in standard laboratory growth medium, and yet they have retained them through decades of culture and can still use them when needed. Lab strains of E. coli have most definitely NOT stripped themselves down to lean mean LB-medium-eating machines with no superfluous genes.
Whilst the 'anything unused is an energy cost' argument makes intuitive sense, it is not clear that a drive to shed unnecessary organs etc. has proved to be significant in our evolution. "Why not" is an interesting debate, but I agree with Michael Lynch et al that the "all evolution is selective" camp have it wrong.
posted by nowonmai at 7:15 PM on June 5, 2007

Well, the plasmid example was just the first thing that came to mind. Of course things are a lot more complicated than that. Especially once you get away from Beadle and Tatum idea, or that many traits/organs/etc are coded for by many different genes.
posted by c13 at 7:24 PM on June 5, 2007

there's not some appendix gene that can be knocked out and suddenly humans won't have a useless appendix anymore

that's also ignoring the appendix's positive purpose in the body: killing the owner after he/she's reached her prime, making way for the following generations.
posted by Heywood Mogroot at 7:25 PM on June 5, 2007

"Purpose" is a very nebulous word. It is limited by your imagination and/or knowledge.
posted by c13 at 7:40 PM on June 5, 2007 [1 favorite]

Tiresias: so, if lifting heavy shopping bags for any extended amount of time (say, greater than three or four minutes) results in lots of pain, redness, and swelling in my hands, does that mean that I don't have the muscle? Or would I just start hemorrhaging?
posted by invitapriore at 7:41 PM on June 5, 2007

The more you discover the less you know.
posted by Burhanistan at 7:42 PM on June 5, 2007

“Why in gods name does the human male's reproductive organs (actually I will rephrase that) - why in gods name does the very sensitive human male's reproductive organs, dangle right out in front of the body, exposed to all the world's fast moving objects, knees and hands?”

As c13 says, the best explanation is that spermatogenesis requires a lower temperature than human body temperature. While having testicles exposed has disadvantages, those disadvantages have less costs than a complex separate internal temperature regulation system—specifically, I suppose, because cooling something below body temperature inside the body is no easy task (in contrast to heating something above body temperature).

I've not read anything other than offhand assertions about this, so don't take my explanation as authoritative.

“Nipples are not vestigial. Males have them because fetuses don't develop sex characteristics immediately. By the time we do, the nipple has already begun to form.”

Yes, in fact I think I stated that exact explanation myself in a recent MeFi thread. But whether this technically/semantically qualifies as "vestigal" or not, nipples qualify for the more general, larger category of "organs that have no use".

More specifically, I think that the nipple example is essentially similar to the explanation for a great many other useless anatomical features—they're developmentally dependent. Either in the most literal sense of an individual's development, or in the evolutionary biological systemic sense where a feature is intimately connected to a biological substrate that other, useful, features rely upon. And then you've got the interdependence of gene complexes, too.

This is one reason why evolutionary processes are so slow. The enormous amount of biological interdependence means that it's almost always difficult to get from point A to point B.

“What I'm saying is that if something is not useful, it is most likely deleterious, simply because it puts and extra energetic load on an organism. ‘Deleterious’ in this case does not necessarily mean ‘bad for the particular organism’, but that it puts that particular organism at a relative disadvantage compared with others in that particular environment.”

I'm not quite sure what you're trying to make clear in that second sentence. The only environment which ever matters, of course, is the environment of adaptation. And the only "bad" is the bad which is disadvantage compared with others in that environment. So the sentence seems to be completely unnecessary.

At any rate, the first sentence is probably more false than it is true. Note that you first stated it even more strongly than you do in this sentence: you gave the impression, anyway, that anything that is unnecessary represents a deleterious trait because of the energy needed to support it.

However, this is false. This isn't the first time I've heard this—I had a roommate who insisted he was taught this in some undergraduate class that dealt with evolutionary theory.

This is what I was criticizing in my earlier comment when I talked about measuring things against an ideal. Evolution isn't a process aiming toward something optimal except in some extremely narrowly defined sense of "optimal". And that optimum doesn't necessarily include greatest ideal energy efficiency.

It could be that the energy expenditure for this useless structure is small enough that it is small enough that the time scale upon which it would be selected against is greater than the time scale upon which larger selection pressures make it a moot point. It could be that the energy expenditure is below a noise threshhold. It could be that the energy expenditure of every possible immediate movement away from that structure is greater than it is keeping it. (In other words, there's no way to get there from here.)

There's lots of reasons why a useless structure won't ever go away. Ever.

Perhaps the so-called "microevolution" (I hate to use that term as it implicitly accepts a distinction that the creationists favor) we directly experience misleads our intuition about this. In less genetically and physiologically complex organisms, there may be fewer barriers to optimizing organisms in this energy efficient sense you are describing. I don't know, I'm not an evolutionist. I'm only speculating.

I do know, however, that the assertion that all useless structures will evolve away is false.
posted by Ethereal Bligh at 7:43 PM on June 5, 2007

Many other mammals can and still do synthesize their own Vitamin C, though humans lost the trait due to an abundance of it in their diet.

I thought this is exactly the sort of thing we're talking about not happening. Wouldn't it need to be a disadvantage to be weeded out? If merely no longer necessary, not affecting survival chances either way, why would it disappear?
posted by dreamsign at 7:45 PM on June 5, 2007

Oh, grouse makes the same arguments I just made in the second half of this excellent comment of his.
posted by Ethereal Bligh at 7:46 PM on June 5, 2007

If merely no longer necessary, not affecting survival chances either way, why would it disappear?

Why would it stay?
posted by grouse at 7:49 PM on June 5, 2007

“that's also ignoring the appendix's positive purpose in the body: killing the owner after he/she's reached her prime, making way for the following generations.”

That's extremely speculative as well as being well within the now very dubious territory of comprehensive group selection theory.

“That's a new one for me. But for many years the prevailing dogma was that the parts of the genome which were not in what were understood to be genes were ‘junk.’”

I also certainly don't think this belief was "sheer human conceit". I don't think it was particular naive, either. By the time that scientists began to understand the genetic code, they'd already been long aware of how sub-optimal much of biology is (sub-optimal, again, in that ideal sense). Why couldn't DNA be sub-optimal in exactly the same way in having lots of cruft?

Turns out that "junk" DNA probably has lots of purposes, including direct functioning we're not yet aware of as well as error-checking stuff. (I know you know this; I'm writing it for the benefit of others.)
posted by Ethereal Bligh at 7:54 PM on June 5, 2007

extremely speculative as well as being well within the now very dubious territory of comprehensive group selection theory

so? and... so?

My general point was that IMV things that end up killing us are not necessarily a bug, but a feature.

if this is "extremely speculative" or a part of some nasty blah-blah-blah theory, so be it, since that's no reason for me to think I'm wrong.
posted by Heywood Mogroot at 8:12 PM on June 5, 2007

If merely no longer necessary, not affecting survival chances either way, why would it disappear?

It's not that it necessarily would disappear, just that there's nothing to stop it. If being unable to make vitamin C is not a disadvantage, then random mutations will mean you will end up with a population in which some people can and some people can't make the stuff. Because there is no selective pressure, the proportion of people in the population who can make vitamin C will, over time, end up being pretty much random. Therefore it's possible that at some time, it might randomly happen that NOBODY can make vitamin C. That might sound pretty unlikely, but if the population goes through a bottleneck, like a few people invent fire and sweep the rest of the population away with that advantage, then there's always a chance of something like this happening. This is called 'genetic drift'. It works either way - it could equally be the mutation that prevents vitamin C production that is eliminated. Natural selection isn't involved so long as it really doesn't matter whether you can make vitamin C or not.
posted by nowonmai at 8:14 PM on June 5, 2007

It could be that the energy expenditure for this useless structure is small enough that it is small enough that the time scale upon which it would be selected against is greater than the time scale upon which larger selection pressures make it a moot point. It could be that the energy expenditure is below a noise threshhold. It could be that the energy expenditure of every possible immediate movement away from that structure is greater than it is keeping it. (In other words, there's no way to get there from here.)
There's lots of reasons why a useless structure won't ever go away. Ever.

You're forgetting the mutation. We humans acquire ~5 new germline mutations over our life-time. If a mutation in a gene does not affect the organisms survival, it will be passed on.
posted by c13 at 8:18 PM on June 5, 2007

“if this is "extremely speculative" or a part of some nasty blah-blah-blah theory, so be it, since that's no reason for me to think I'm wrong.”

Well, the same can be said of creationism by its believers. Their ideas seem reasonable to them even though it's part of some blah-blah-blah theory and is extremely speculative. If those aren't handicaps in your opinion, then I really can't ague with you about it, can I?

Anyway, this same argument has been promoted to explain senescence. But the essential problem with it is actually explaining a mechanism by which selecting for this would occur.

Another problem with it, of course, is that your argument applies to everything post-reproductive age. Why don't we have a compulsion to kill ourselves after reproductive age rather than some piddly, random "sometimes an appendix kills you" thing?
posted by Ethereal Bligh at 8:50 PM on June 5, 2007

“You're forgetting the mutation. We humans acquire ~5 new germline mutations over our life-time. If a mutation in a gene does not affect the organisms survival, it will be passed on.”

Forgive me, but I'm not following your reasoning here. Could you elaborate?
posted by Ethereal Bligh at 8:50 PM on June 5, 2007

“It's not that it necessarily would disappear, just that there's nothing to stop it.”

Yes, in this case. Did I miss the part in this subdiscussion where it was made clear that Vitamin C production is not analogous to every unnecessary trait?
posted by Ethereal Bligh at 8:54 PM on June 5, 2007

Sure. We randomly acquire mutations that get passed on to our progeny. Now, suppose some of those mutations happen in a particular "unnecessary" gene. Since this new allele is not detrimental, there is no reason for the mutation to go away. But your progeny will no longer have whatever it was that this gene was coding for. (I'm really simplifying here, but you get the point). The "junk DNA" is actually too conserved across species to be real junk. But it does not code for anything, so what is it? Maybe it is nothing more but mutated genes for stuff we don't need anymore, like feathers or hooves. Nothing keeps them from mutating away because if you pass on an extra mutation in you feather gene to your son, he won't be worse off.
posted by c13 at 9:04 PM on June 5, 2007

Oh, well, there's some confusion of levels going on here, I think. First, the context of the discussion is phenotypical traits and the genes which control them. Second, the word gene can be used in the technical molecular biological context, or in the evolutionary ecological context. It means something different in each. In the molecular context, it is a unit described by molecular structures. In the ecological context, it is an abstracted unit which represents the biological "unit" controlling the expression of a trait.

Now, your argument relies upon your use of the word gene and your use of the word useless in a way in which mixes these two different levels of description—which is an error.

We're talking about phenotypical traits which we are describing as "useless". This doesn't mean that the genes that code for those traits are themselves "useless". They can be. Often they're not.

There's two ways in which this can be the case. The first is that the trait is coded for by the ecological gene, which is described at the level of molecular genes as a gene complex—and with the frequent multi-use of individual genes, portions of that gene complex are not unnecessary with regard to the other traits for which they code.

The second way in which this can be the case is that all those mutations without that unnecessary gene result in traits that are themsleves selected against. I'm not sure how to describe this in a way that doesn't just translate into something equivalent to my previous paragraph, but I'm pretty sure that this exists as a something distinct. Hmm. For example, there's no mutation which actually simply turns off a trait, there are only mutations which replace the useless trait with something that is actually selected against. Sometimes there's not actually an "off" option.

Your argument relies upon an isomorphism of "unnecessariness" between a trait and the gene(s) which select for it. And that rarely applies except for the simplest structures.

Again, I'm not an evolutionist. We're at my horizon of competence. I think that my basic objection to the claim that unnecessary structures will always go away is essentially correct. Beyond that, I'm not sure. Speculating past that horizon, it seems to me that there's some tension here between the descriptive view of the adaptationist paradigm (which I hold to) and its abstractions which, it seems to me, see genes as these units, and the descriptive view of the complexity of the actual biochemistry from which this abstraction of adaptation arises.

I'm tempted here to invoke complexity, in which my own doctrine of the relativity of "appropriate levels of description" applies and within which the pseudotension¹ between the abstraced, higher level description of adaptationism and the reductionist, lower-level of molecular biology is explained. But that is well outside my horizon of competence and is only reliable insofar as the combination of my intuition on complexity (where I have high competency) and the applicability of complexity to this system (where I have moderately low competency) is reliable.

1. Correctly referred to thusly only if my invocation of complexity is appropriate.
posted by Ethereal Bligh at 9:44 PM on June 5, 2007

If merely no longer necessary, not affecting survival chances either way, why would it disappear?

Why would it stay?

Because carriers of the gene survive in equal proportion to non-carriers?

I take your bottleneck example, nowonmai. It does sound unlikely. I bet there is an interesting story in there.
posted by dreamsign at 9:44 PM on June 5, 2007

the same can be said of creationism by its believers

and with "continental drift" back in the day.

Their ideas seem reasonable to them even though

Which is irrelevant. Either their ideas explain the data and/or make testable predictions, or they don't.

Anything new and unproven is "highly speculative". I lack the education & motivation to research what the group selection thing you're talking about -- whether this idea actually falls under it, and whether it is so unloved as you say -- but I consider it self-apparent that any physical defect that kills us after say age 40 (after one's progeny is actively procreating) isn't going to be necessarily selected out and could in fact be selected IN, when considering group-effects like food scarcity issues.

Absent any survival utility of having an appendix, I don't see any reasons why this hypothesis would be disagreeable, group selection theory or no.

Why don't we have a compulsion to kill ourselves after reproductive age rather than some piddly, random "sometimes an appendix kills you" thing?

Contingencies of human development, of course.

The multitude of potential ways our physical bodies will kill us -- heart attack, senescence, cancer, etc -- mean the development of the tricky biological flip from conscious self-preservation to self-destruction was quite unnecessary.
posted by Heywood Mogroot at 9:45 PM on June 5, 2007

I knew a woman who didn't have the fifth little toe, and she did not walk well at all, so I think we need it (or we need the other four toes to be bigger).

I've also read cases in an emergency situation (mother dies after childbirth in a deserted area), where a man has been able to provide breastmilk to keep the child alive. This seem so rare and unlikely to be possible in most cases, that it probably is not reason enough for male nipples, but it's an interesting thought.
posted by eye of newt at 9:48 PM on June 5, 2007

Yeah, males can be produce breast milk. I'm not sure there's data to tell us how large a portion can, but we certainly know that they can under some circumstances. And not merely by virtue of a hormonal "abnormality", which is the trivial case. I think you can get a lot of men to produce milk just by a constant stimulation of the glands. I do think, though, that the milk produced isn't very high quality or quantity.

That said, this is so rare that it's hard to argue that human male milk production actually is an adaptation in its own right.
posted by Ethereal Bligh at 10:24 PM on June 5, 2007

Metafilter: Correctly referred to thusly only if my invocation of complexity is appropriate.
posted by troybob at 11:08 PM on June 5, 2007 [1 favorite]

Heh. That particular sentence is probably a preeminent example of both my voice and a self-satire of it.
posted by Ethereal Bligh at 11:12 PM on June 5, 2007

I love it. It's my sentence of the week.
posted by troybob at 11:13 PM on June 5, 2007

Having fallen hard on my coccyx almost two weeks ago now and it still hurts like hell I'm voting to get rid of it. Could I have broken it? I suppose I would really know if I had done that.

posted by maxwelton

maxwelton, I broke coccyx years ago in a snowboarding accident. The doctor told me I'd turned it into powder.

If yours still hurts like hell, you probably broke it. Get an x-ray and you'll know for sure.

Mine took two months to heal. During that time, it never stopped hurting; nothing made a difference: sitting standing, walking, lying flat ... joke notwithstanding, you can't put your ass in a sling.

To this day I can't sit on hard surfaces for too long at a stretch.
posted by bwg at 11:16 PM on June 5, 2007

“I love it. It's my sentence of the week.”

Except that perhaps it should start with "well" and include an ostentatious and stylistically counterpointal vulgarism or informality—fuck neatly exemplifying both. Also, an em-dash. Therefore: Well, fuck—it's correctly referred to thusly only if my invocation of complexity is appropriate.
posted by Ethereal Bligh at 11:19 PM on June 5, 2007

Invitapriore: This is quite late, and you're probably not even going to read this, but it's incredibly easy to tell whether or not you have a Palmaris Longus. The tendon is actually visible when you clench your first tightly...hold on, consulting my anatomy texts...

Okay: make a fist with your left hand and dig your fingers in as hard as you can; don't hurt yourself, I mean, but do it hard enough that the tendons in your forearm --- which is the say those weird cables that run along your wrist --- are visible. Turn your forearm so that your wrist is facing up and you can, you know, see them. Or feel them. Or palpitate them, if you want to feel very medical.

Now here's what's going to happen if you happen to have a Palmaris Longus. Assuming you're using your left hand, and do use your left hand because it saves us having to use technical words like lateral or medial, there are going to be two very obvious tendons running almost straight down the center of your forearm, and then one maybe 3/4 of a cm to the right of those. Don't dig to deeply here: if you push hard enough, you'll feel all sorts of tendons, and then who knows what kind of muscles you're touching. These should be fairly obvious, meaning that maybe you can probably see them, and even if you can't at the very least you shouldn't have to dig around too hard to find them. It's hard to describe exactly, because there is a huge amount of diversity from one person to the next, so treat these as general guidelines. Regardless of your own personal anatomy, we're looking for very superficial tendons that are noticeably distinct from the more profound tendons beneath.

Assuming you have a Palmaris Longus, the leftmost tendon belongs to Flexor Carpi Radialis, which flexes your wrist as well as abducts it, which is to say pulls it to your left (left hand.) The rightmost tendon belongs to Flexor Carpi Ulnaris, which flexes and adducts your wrist joint, or, as you might imagine, pulls it to the right. The middle one, which should be closer to the Flexor Carpi Radialis (and roughly parallel with it) than it is to Flexor Carpi Ulnaris is our man Palmaris Longus. (By the way, the Flexor Carpi Ulnaris, or the muscle on the right, tends to be a little deeper than the other ones so feel around a little harder for it. If you have no significant problem with your wrist movement, believe me, it's there.)

If you don't have a Palmaris Longus, there won't be a middle tendon. That's all I can tell you: there will be a tendon on the left, and a tendon on the right. If you have a Palmaris Longus, then there will be one in the middle, close to the one on the left.

If you don't have one, I wouldn't fret it. All the Palmaris Longus muscles does is pull on the Palmar Aponeurosis. The Palmar Aponeurosis is nothing more than a band of connective tissue that is maybe 1.5 cm long from wrist-side to fingertip-side, and runs the width of your hand, right down the middle, parallel to your palm lines. In cadavers at least, the tendons of the forearm look and feel like nothing so much as the cable that plugs your telephone into the wall. They're kind of silvery, they're incredibly tough and they almost feel like you could stretch them if you tried, but of course you actually can't. Likewise, aponeuroses look and feel likethey would work like shopping bag plastic --- thin and fragile-looking. Except that they are much, much, much stronger than plastic: there is no way you're going to rip apart an aponeurosis without a scalpel. Even then, you're going to have to use force and a sawing motion (which you're not supposed to do, but I do, because I'm not nearly as good at the dissections as I'd like to let on here). Please don't try this at home, by the way.

Anyway, massive side track aside, regardless of whether or not you have a Palmaris Longus, you have a Palmar Aponeurosis. If you do have a Palmaris Longus, what it does is attach to the Palmar Aponeurosis, and if you're carrying a load in your hand, it contracts (weakly: it's a weak muscle.) When this happens, it tenses the Palmar Aponeurosis, pulling it taught. Now, and I should have mentioned this earlier, the Palmar Aponeurosis runs above the arteries in the hand, so when it's pulled taught, it offers some resistance to whatever weight might be compressing them. Not fully necessary, because there's a lot of redundancy built into the blood supply to the hand, but useful. Like many (but by no means most) things in the body, it's a simple and elegant solution to a complex problem.

You can live happily without a Palmaris Longus and not even notice. Hell, you can live happily without a cerebellum and not even notice. But it's a useful thing, and not only is there no selective disadvantage against it, but it's common enough that it's not likely to be lost to genetic drift, and given that humans, with a very large pan-geographically dispersed population and essentially no real chance of genetic isolation, have pretty much ceased to speciate, Palmaris Longus ain't going nowhere.

If you really want to look at evolutionary-based weirdness, Christ, all you have to do is look at the course of the Vagus nerve. But that's a story for another time.
posted by Tiresias at 11:51 PM on June 5, 2007 [4 favorites]

On a side note which has nothing to do with anything at all, 'lateral' and 'medial' are two of the most shockingly useful words available to the English language, and yet they are somehow not in the common lexicon. If this were the kind of thing you could vote on, I would vote that we include them. Likewise for saggital and coronal.
posted by Tiresias at 11:51 PM on June 5, 2007

Hell, let's just cull all of the introns, like they did in those mice, and check out our mutant offspring.

Hey, aren't we already doing this with cellphones and reality TV?
posted by Sonny Jim at 12:28 AM on June 6, 2007

Tiresias, the word is palpate, not palpitate. And it's taut, not taught.
posted by mokey at 1:39 AM on June 6, 2007

On a side note which has nothing to do with anything at all, 'lateral' and 'medial' are two of the most shockingly useful words available to the English language, and yet they are somehow not in the common lexicon. If this were the kind of thing you could vote on, I would vote that we include them.

I vote for "distal."
posted by grouse at 2:47 AM on June 6, 2007

...humans, with a very large pan-geographically dispersed population and essentially no real chance of genetic isolation, have pretty much ceased to speciate...

They do what with the who now?
posted by Jofus at 5:39 AM on June 6, 2007

Interesting read for the most part, but was this part a joke?

PYRAMIDALIS MUSCLE

More than 20 percent of us lack this tiny, triangular pouchlike muscle that attaches to the pubic bone. It may be a relic from pouched marsupials.

A relic from our pouched marsupial ancestors?

Man did not evolve from apes but from wallabies! Wow - Darwin was stoopid.
posted by batou_ at 5:56 AM on June 6, 2007

Man did not evolve from apes but from wallabies!

Humans are apes. And saying we evolved from a common ancestor with marsupials is not the same thing as saying we evolved from wallabies. But I thought the common belief was that metatherians (marsupials) and eutherians (placental mammals) evolved separately from a common therian ancestor, not that the marsupials are our ancestors.
posted by grouse at 6:22 AM on June 6, 2007

Apes were a beta testbed for the thumb module.
posted by Burhanistan at 6:57 AM on June 6, 2007

Tiresias, the word is palpate, not palpitate.

I find your lack of faith... disturbing.
posted by ROU_Xenophobe at 8:13 AM on June 6, 2007

I was actually tempted to go to my doctor with this article printed out and say "I want to know if I have these things! It's important to me! You deal with hypochondriacs and overprotective parents and nonsense all day long, now spend time finding my evolutionary vestigial muscles!"*

But, thanks to Tiresias, I can check one off of the list. Yes, I have Palmaris Longus muscles. Hurray!

Now if only I could figure out how to determine if I have a Pyramidalis...and whether it could be used for nefarious purposes...

* Not a pick-up line, I swear
posted by Katemonkey at 8:54 AM on June 6, 2007

For some reason, this article really bothered me.

On what basis are we supposed to decide that a trait is 'useless' or a gene is 'broken'? For all the popular denunciations of creation 'science', Discover's take on evolution presents a worldview that is not too far off from one that claims humans to be at the top of the great chain.

The underlying message of this article is that 'once upon a time we needed these things, but now we're advanced enough that our bodies are becoming obsolete.' It says more about what happens to be important to us today about our bodies than the 'real value' of any part of our anatomy. Let's all go forth and downsize our companies, our governments, and now the little useless bits of flesh hanging off our bodies!
posted by mariokrat at 9:52 AM on June 6, 2007

Hey, something changed! Does it keep me from making babies? No? Hell, let's keep it!
posted by goodnewsfortheinsane at 10:45 AM on June 6, 2007

"science still can’t offer a full explanation for why one outdated anatomic trait lingers in the gene pool"

The key word there is "outdated" ... we don't, yet, know enough to be sure what's "outdated".

And that's because biochemistry is extremely complex; new discoveries are happening almost daily. It's certainly unreasonable to expect brains to decode in a mere century what evolved over 4 billion years in a wide variety of environments.

Assume, though, that some DNA is junk. What process might lead to its removal? Evolution. If there's no, or only a small, disadvantage in carrying it, what does it matter? If there is, then eventually, like excess body hair, it will be pruned. Possibly by evolutionary processes that are too subtle for us to detect yet (but that's speculation, not science).
posted by Twang at 4:25 PM on June 6, 2007

Assume, though, that some DNA is junk. What process might lead to its removal? Evolution.

Its removal is evolution, so that is a tautology. Saying "evolution led to its removal" does not explain anything. If you said that one of the processes of evolution, such as natural selection or mutation, led to its removal, that does explain something.

If there is, then eventually, like excess body hair, it will be pruned.

No, you cannot predict the pruning of the disappearance of a deleterious allele with certainty. Genetic drift means that deleterious alleles frequently fixate in populations, eliminating more advantageous alleles from the gene pool.
posted by grouse at 4:46 PM on June 6, 2007

Tiresias: thanks! I do indeed appear to have it, which means no getting out of buying/carrying the groceries any time in the near future.
posted by invitapriore at 7:21 PM on June 6, 2007

Also, interestingly (though now YOU'RE probably not reading this), the tendon corresponding to the palmaris longus is, of the three, by far the most apparent, most notably with fingers extended.
posted by invitapriore at 7:28 PM on June 6, 2007

I know I'm late to the party, but that joke about the extra cervical rib... god... I need to go lie down.
posted by tehloki at 9:30 PM on June 6, 2007