This is the kind of post I envisioned writing—once every few weeks or so—when I started this website. My intention was to use the site to publicize new evidence for evolution. Not that we need any to show that that well evidenced theory is true, of course, but to support the book and alert people to cool new findings. But, as I’ve said, things got out of hand, and so we have cats, food, travels, religion, and so on. So let’s go back to our roots today. . .
Matthew, on the job as always, sent me this tw**t and asked me if I’d mentioned this in the “vestigial structures” section of Why Evolution is True.
Today's bloody brilliant fact: 35% of humans are born with vestigial muscles in the top lip that allow for mammalian whisker-wiggling. pic.twitter.com/hsymmituzD
— Jules Howard (@juleslhoward) June 19, 2017
I told him I hadn’t even heard of this, but, sure enough, I found the following in the “Human vestigiality” article in Wikipedia (worth looking at):
In many non-human mammals, the upper lip and sinus area is associated with whiskers or vibrissae which serve a sensory function. In humans, these whiskers do not exist but there are still sporadic cases where elements of the associated vibrissal capsular muscles or sinus hair muscles can be found. Based on histological studies of the upper lips of 20 cadavers, Tamatsu et al. found that structures resembling such muscles were present in 35% (7/20) of their specimens.[50]
Naturally I went to the cited source: a short paper by Yuichi Tamatsu et al. in Clinical Anatomy in 2007 (reference and link below; free access if you have the legal Unpaywall application). That paper shows what to me (and I’m not an anatomist) looks like vestigial muscles that are the remnants of muscles that move the whiskers in our mammalian relatives—and in our whiskered ancestors.
Mammalian whiskers are called “vibrissae” and most are are movable (their function is at least partly tactile–touch–though they may have other functions). As for how and why they move, here’s the Wikipedia entry:
The follicles of some groups of vibrissae in some species are motile. Generally, the supraorbital, genal and macrovibrissae are motile, whereas the microvibrissae are not. This is reflected in anatomical reports that have identified musculature associated with the macrovibrissae that is absent for the microvibrissae. A small muscle ‘sling’ is attached to each macrovibrissa and can move it more-or-less independently of the others, whilst larger muscles in the surrounding tissue move many or all of the macrovibrissae together.
Amongst those species with motile macrovibrissae, some (rats, mice, flying squirrels, gerbils, chincillas [sic], hamsters, shrews, porcupines, opossums) move them back and forth periodically in a movement known as whisking, while other species (cats, dogs, racoons, pandas) do not appear to. The distribution of mechanoreceptor types in the whisker follicle differs between rats and cats, which may correspond to this difference in the way they are used. Whisking movements are amongst the fastest produced by mammals. In all whisking animals in which it has so far been measured, these whisking movements are rapidly controlled in response to behavioural and environmental conditions. The whisking movements occur in bouts of variable duration, and at rates between 3 and 25 whisks/second. Movements of the whiskers are closely co-ordinated with those of the head and body.
You might remember that we evolved from a shrewlike ancestor, and thus probably an ancestor that could move its whiskers.
In their paper, Tamatsu et al contrast the whisker muscles (muscles of the “sinus hairs”, another name for vibrissae) with those of regular body hairs. The latter have smooth “arrector pili” muscles that can erect each hair involuntarily during times of cold or fear, giving us goose bumps. As I note in WEIT, these are probably vestigial in humans, as we have no need to look bigger by erecting our hairs (versus cats, who bush out when they’re threatened), and erecting our body hair in the cold doesn’t provide much thermal insulation since we’re “naked apes”. Arrector pili appear to be remnants from mammalian ancestors who could really use these muscles adaptively, and thus they give testimony to our evolution.
Here’s a drawing showing the arrector pilus, the orange-red band affixed to the hair follicle at center left:
In contrast, whiskers are attached to special “capsular muscles” and can be moved voluntarily; unlike the smooth arrector pili, they are striated, or “striped”, as voluntary muscles are.
Tamatsu et al. looked for these capsular muscles by dissecting 20 cadavers (11 males and 9 females) and doing scanning electron microscopy of sections of the upper lip. They found what looked like capsular “whisker muscles” in 4 males and 3 females, or 35% of the sample. I won’t go into detail, but will just show a few of the photos they present as evidence, along with their captions (indented). Note the striated muscle in (b), which you can see better two pictures down:
Sections through the upper lip. a: Light micrograph of a section of the upper lip region of a 76-yearold female. The right side of the figure is medial and the left side is lateral. Arrows indicate the location and direction of muscle fascicles. The fascicles diverge from the orbicularis oris layer and course to the dermis (D). SC, subcutaneous tissue; ML, muscle layer. Azan-Mallory stain. b: Magnified light micrograph of the rectangular, outlined area shown in (a). The arrows indicate the course of a muscle fiber having a striated pattern and collagen fibers. This bundle courses to a hair follicle (HF). [Scale: bar = 1 mm in (a) and 0.5 mm in (b)]
Higher magnification light micrograph (c) and SEM micrograph (d) of the rectangular, outlined area shown in (b). Arrows indicate an attachment area between the hair follicle and collagen fibers continued from the muscle fiber located in the subcutaneous tissue. [Scale bars: 250 microns in both photos]
Here the striated muscle is seen clearly:
High magnification light micrograph of the small rectangular outlined area shown in (b). A striated pattern can be seen in the muscle fiber. Scale bar = 25 microns
The authors conclude that these muscles are similar to those that move the whiskers in mammals that have them:
. . . in the sections that displayed vertical sections of hair follicles it was observed that these muscle and collagen fascicles surrounded the outer half of a hair follicle. This configuration is different from arrector pili muscles of body hairs that attach to the follicle at a single point, but shows similarity to muscle slings of mystacial vibrissae reported by Dorf (1982). According to his report, muscle slings of mystacial vibrissae embraced the follicles. Furthermore, we found many blood vessels containing blood cells near these follicles. Because of their thin walls and large diameter, these blood vessels were assumed to be veins, which are known to be associated with sinus hair follicles. Our findings of the structural characteristics of these muscles and follicles, which bear similarities to those of sinus hairs, led us to conclude that the observed muscle fascicles are a vestigial muscle of sinus hair. A 35% incidence supports this conclusion, given that regressive organs do not exist in all individuals.
Vestigial structures like wisdom teeth and ear-moving muscles often are missing in many individuals—one of the signs that the feature is of no or little use. Now you’re probably asking yourself, if you’re a man, “If I had a mustache, could I move it if I were one of the individuals that had these muscles?” Or, if you have a mustache, you’ve probably already tried to move it as you read this. But no dice, for a mustache is not the equivalent of mammalian whiskers. A ‘stache is made of regular body hair and thus, while it could be moved by arrector pili, its hairs cannot be moved voluntarily.
Let’s take the finding of Tamatsu et al. as tentative but very suggestive, as the authors knew what kind of muscle to look for and found it. And we have no vibrissae. And the muscle is present in only a fraction of individuals, and in females, too. This looks to be an anatomical remnant of our whiskery ancestry: a vestigial trait that testifies to the fact of evolution.
____________
Tamatsu, Y.; K. Tsukahara, Kazue; M. Hotta and K. Shimada. 2007. “Vestiges of vibrissal capsular muscles exist in the human upper lip“. Clinical Anatomy. 20(6): 628–31.
This is very cool.
I wonder what the proportion of humans retain the ear wriggling ability. (this one does).
Would tongue curling also be a similarly vestigial ability? I am aware there is a small proportion who are unable to do that, and there is no obvious benefit to the ability.
I was about to pose the same questions. Also wiggling one’s nose. I’ve never been able to do any of that, but I wonder if any of them have to do with the presence of vestigial muscle/s.
And nostril flaring 🙂
Wait, not everyone can flair their nostrils? I didn’t know that.
It seems to me that being able to flair one’s nostrils still has use, as it conveys certain emotions.
I suspect that with traits like this, it’s more like most people have the circuitry, they’ve just never tried to enervate it. For many yrs I could wiggle just one ear. Then one day – I think when I was in high school an, having nothing better to do, it occurred to me that if I could wiggle one, the nerves to control the other ought to be there too. But how to find a circuit you’ve never used. All I remember is I concentrated on it and soon enough I could wiggle the other one.
I spent months learning how to wiggle each of my toes individually back when I was in high school.
You can probably guess what my social life was like.
Had you success?
Absolutely! I wish I’d continued practicing that because my social life hasn’t changed much.
” a vestigial trait that testifies to the fact of evolution”
Or a sign of God’s sneakiness! Planting false clues to confound the doubters.
Yep, Loki sure is clever.
Very interesting post.
Yes, a very nice return to the site’s roots. Bravo.
“You might remember that we evolved from a shrewlike ancestor”
Meaning … the most recent common ancestor of all mammals, the MRCA of all placental mammals, the MRCA of all members of the tree shrew-colugo-primate superorder, or?
Placental mammals. See here: https://www.theguardian.com/science/2013/feb/07/ancestor-humans-mammals-insect-eater
Thanks!
One of my ladyfriend’s sisters is still at shrew level.
“A ‘stache is made of regular body hair and thus, while it could be moved by arrector pili, its hairs cannot be moved voluntarily”
Such a pity – what a spectacle it would have been to see PCC[E] if the era of the photos on the previous item, wiggle his moustache as he can his ears. If you have not seen him do that insist that he does if you ever meet in person!
🙂
Very interesting – Science scores again!
Drat! I’d grow one again if I knew I could wiggle it now.
Not everyone can curl their lips up towards their nose for underwater dolphin kick on back. I wonder if this percentage (35%) of humans is about the same as those who have vestigial muscles on the top lip for mammalian whisker-wiggling.
Elite swimming requires lots of subtle but adept control of lips for many types of strokes. I would not be surprised if most elite swimmers had these muscles.
Wait a minute–you are saying swimming strokes are contingent on the position of your lips?
Well yeah. Swimming really fast freestyle requires that you mouth hardly leave the wake formed by the front of the head. The amount of turning the head to the side is minimized by pursing the lips sideways. Those muscles are on the side of the face, but adept lip control can help a lot.
Breathing out is also very important; pursed lips are common above and below water. And unless a nose clip is used, swimmer must push their lips close to the nose, so water will not enter the nose when kicking underwater on their back.
It is likely swimming has a little bit of selection for this process. Just as swimmers tend to have better flexibility in their shoulders than the average person, I would guess there are might be more swimmers at an elite level who have greater control of their lips.
Jerry: I’ve always been curious about why wisdom teeth are vestigial? Why did our evolution progress in a way that found them less important than, say, the back molars next to them? I mean, I understand why you need as many molars as we have, but why not one more set? Do you know of any good explanations or any papers with some that you can pass on?
Also, I meant to note that the presence of these newly discovered muscles bring people closer to catliness, and thus, closer to godliness 🙂
Time for another study – are these muscles more prevalent in cat owners?
I am not sure but I seem to recall an explanation that involved the jaw evolving to be smaller and less robust as the brain evolved to be larger, thus leaving not quite enough room for all the teeth that our earlier evolutionary history granted us.
This explanation seems to assume that overall skull size was constrained such that it wasn’t likely that the skull could evolve to retain larger jaws and an enlarged brain case at the same time. I’ve no idea why that would be. Too “expensive” to support a head over a certain size?
Hopefully someone who knows better will chime in.
That is how i had heard of it too. It is proposed to be a matter of jaw size.
What you are describing seems unlikely to me as that would amount to negative selection for those molars. One would expect them to be lost under the “skull has to get bigger and the jaw can’t keep up” evolutionary pressure, not retained as vestigial structures. No?
It seems parsimonious to me to suppose that since the third molars are an adaptation to an herbivorous diet – the likeliest explanation for them becoming vestigial is that our ancestors became more generalist in their diets, obviating the need for those molars. The developmental, metabolic and reproductive costs to making them are so small that there is no strong selection against them. So we still have them.
I wouldn’t consider myself well informed on this topic but from what I understand nearly all people have wisdom teeth. Given that, or even if merely a high percentage of people have wisdom teeth, I’d say that yes that seems to clearly indicate that there has been little significant selection pressure against wisdom teeth.
I think the main point is that the human jaw has become too small to contain all the teeth we still have. There has been selection pressure to decrease jaw size but none to decrease the number of teeth. Add in that wisdom teeth are the rear-most teeth, and they erupt last, and you arrive at wisdom teeth getting a bad rap for being the teeth responsible for causing all the problems in a mouth that is too small to fit all the teeth.
They certainly are worse than useless these days!
These folks have some evidence that it was diet change itself that changed jaw size, though it is far later than I supposed. They tie it to recent changes in our own species (the development of agriculture) not some distant ancestor!
One reason I keep coming back to WEIT; ILSNED!
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0117301
I don’t know in general, but my jaws just don’t have room for another big tooth. My teeth are crowded and two are crooked even though the wisdom teeth were removed.
Our ancestors were herbivorous and the 3rd molars were needed for their diet. The thinking is that as we switched to a generalist diet, they were no longer needed.
In about a third of people they develop abnormally and become impacted, in many people they don’t even erupt from the gums and they can cause serious illness and death.
In my husband’s case, one of them grew in sideways under the gum and ground off the root of the molar next to it. The dentist who performed the surgery invited all his compatriots in to take a gander at this as, seemingly, it was quite rare. It was not a fun experience.
Whereas, I, had wisdom teeth that erupted without difficulty and when the molar next to one of them had to be pulled, the wisdom tooth moved over to take up it’s function.
My wisdom teeth were both miserable affairs. The root grew from a place directly under the next molar. They had to be excavated and broken to get them out. It took a long time. It was not fun. Each tooth took weeks to heal. I’m glad I’ll never have to endure anything like that again (knock on wooden teeth).
As I see it, the reduction of the jaws in human evolution does not leave enough space for wisdom teeth to be well-built and fully functional. My lower wisdom teeth could grow only by displacing the other teeth, particularly the incisors. They ruined my potential Hollywood career!
I’m not much for facial hair but if I could grow a mustache like that, I might change my mind.
I’ve never heard of these vestigial vibrissae vibrators before. Fascinating, and an excellent example of just the sort of thing you would expect to find if evolution were true.
I think ear-wiggling ability is more a function of having voluntary control over the branches of the facial nerve that innervate the external auricular muscles, i.e. you would have good representation of these muscles for the homonculi in your primary motor cortices. I’ve dissected this region in many cadavers, and I don’t recall the auricular muscles (3 on each side, with auricularis posterior being the largest) being absent for any of them. Students might claim that they’re missing, but this is usually because they’ve botched the dissection or just give up trying to find something.
A quick search on PubMed revealed that there is a “rare” muscle in humans called the styloauricular, which acts to abduct the auricle (external ear; move it away from the head) – animals like elephants that flap their ears would have well-developed similar muscles. Also saw a paper on using commands to the posterior auricular muscles/computer interface to allow quadraplegic individuals to move their wheelchair.
Too bad we didn’t keep the whiskers that could be individually controlled by these muscles and have it all co-opted for sexual signaling.
Full disclosure: I have had a mustache for 49 years.
If this pans out it is not only more confirmation of our evolution it confirms that fairly precise predictions can be made on the evidence gathered from studying ancestoral line and similar beasties.
Interesting!
Micrograph ‘c’ shows a hair follicle (HF) linked by collagen strands to the vestigial muscle fibers. Doesn’t this suggest that the ‘hair follicle’ labeled in the micrograph is a vestigial ‘vibrissa follicle’? Or am I reading things wrong?
And yes, I did try to quiver my mustache when reading the piece, but failed.
I tried and failed as well. My feeling of inadequacy was not buoyed by my cat’s smug expression.
I went to the link and unpaylink said it couldn’t find a legal copy. The post has lots of detail though.
It worked for me at that link.
Some whiskers are sense organs. Do the people who can wiggle also get more sensory nerves?
Reblogged this on The Logical Place.
Cool.
Cold and fear aren’t the only things that can trigger arrector pili. I get goosebumps listening to music and watching ballet. So I’d argue that these muscles aren’t vestigial in the sense of having no current adaptive function; rather, they’ve been exapted as part of our emotional response system. Getting goosebumps is as integral to our internal sense of what we’re feeling as pounding pulse or breath catching in our throats, and people without such awareness would be emotionally crippled in important ways.
By the same token, it seems somewhat off the mark to classify these responses as involuntary, since they can be invoked by particular mental states. Actors are adept at summoning such responses on demand, and the rest of us can do it too if we put our minds to it. Yes, there are smooth muscles and striated muscles, but it seems that both are subject to some degree of voluntary control.
Coincidentally, I experienced goosebumps listening to Duelling Banjos in an earlier post. Just at the part where it “takes off”.
The division between “voluntary” and “involuntary” seems to mask what is a matter of degree rather than dichotomy, no?
Nice! Keep the evolutionary science coming!
Very interesting stuff, thanks!
I remember reading about Count Octavio Meral in Ripley’s Believe It or Not; here’s an online account about what he could (allegedly) do with his hair:
http://yetanotherengineer.blogspot.com/2008/06/believe-it-or-not.html#!/2008/06/believe-it-or-not.html
Don’t know if this info is relevant, but you must admit it’s intriguing.
BTW, my favorite slam-dunk argument for evolution is the recurrent pharyngeal nerve example. How anyone can look at that and still discount evolution boggles my mind.
Is that a lorax in that photo?
I think the two best known muscles that are sometimes absent are accidental deletions rather than vestigial structures present in some, and I say that as they are present in most people: palmaris longus and serratus anterior.
However, related to vestigial whisker twitches, we still have platysma – also a muscle inserted onto the skin, and present in a thin sheet over the neck, shoulders and upper chest. It’s function used to be to make the skin shiver convulsively to get rid of biting flies – just watch a horse on a warm day and you’ll see it in action over most of the body. I don’t think I have ever heard of a human with voluntary or even involuntary control of it, so I’d guess it will be gone from our bodies at some point in the future.
Sub
An FYI on this work, a team has done follow up work on the evolution of vibrissal sensing in mammals:
Grant, Robyn A., Sebastian Haidarliu, Natalie J. Kennerley, & Tony J. Prescott. 2013. “The evolution of active vibrissal sensing in mammals: evidence from vibrissal musculature and function in the marsupial opossum Monodelphus domestica.” The Journal of Experimental Biology 216 (15 September): 3483-3494.
Mitchinson, Ben, Robyn A. Grant, Kendra Arkley, Vladan Rankov, Igor Perkon, & Tony J. Prescott. 2011 “Active vibrissal sensing in rodents and marsupials.” Philosophical Transactions of the Royal Society of London B (Biological Sciences) 366 (November): 3037-3048.