Why do muscles hurt after exercise?

As long as I’m stranded in a snowstorm (thankfully fading right now) and unable to teach my human physiology class this morning, I thought I’d at least put a small part of the story I was going to tell on the web. We’re currently talking about muscle physiology, and I’ve already gone over the sliding filament theory of muscle contraction…oh, you know that one, right?

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Muscles contract using interlaced filaments of myosin (in red, above) and actin (blue), and myosin acts as a kind of motor gear, burning ATP to ratchet the actin filaments along their length, shortening the muscle. The ratchet functions whenever the cell has ATP and also is flushed with the release of calcium from internal stores, which is the chemical trigger to initiate a contraction. But you knew that already.

You also knew about basic metabolic biochemistry, the process that breaks down sugars to release energy, which is captured in the form of ATP and various reducing agents.

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All you need to remember to follow along is that there is the glycolytic pathway, which snaps a 6-carbon sugar in half to produce two 3-carbon fragments and a little bit of energy, and that there is the rest of the biochemistry shown here, which takes the 3-carbon fragments and burns them down the rest of the way to CO2, producing a lot of energy in the form of ATP. Unfortunately, that second, very efficient part is dependent on the availability of oxygen, so in many cases, where your muscles are working harder than the respiratory/circulatory system can deliver oxygen to them, they are only doing the glycolytic part of the process.

Like I said, though, you already knew all that. I was planning a quick review of these basics this morning, and to discuss factors that influence strength and endurance in muscle activity, and then to answer the one question I’m addressing here: why do my muscles hurt after exercising?

There are actually a couple of reasons. One that you may have heard of before is lactic acid buildup, but this is actually only a short term concern. Lactic acid is a byproduct of glycolysis. If you’re working hard, you can’t deliver oxygen to the muscles as fast as they need it, so they rely almost entirely on the glycolytic pathway for energy, which in my diagram above has three products: ATP (which the cell wants to use for contractions), and pyruvic acid and the reducing agent NADH2, which the cell is unable to use at that time because of the lack of oxygen. What the cell does to keep the unusable products from accumulating and bringing the glycolytic pathway to a halt is, in short, to use the reducing agent to convert pyruvic to lactate, which then diffuses away into the bloodstream. Later, when you’re taking it easy and recovering from your workout, the lactate will be recovered and reprocessed to recover more ATP and also to rebuild some of the glucose that was burned.

(Scratch much of the above paragraph. While many physiology textbooks state that lactic acid accumulation is a problem, the biochemists say otherwise: what builds up is lactate, which doesn’t acidify the tissues and can actually act as a buffer. The source of acids that cause the transient ache are the hydrolysis reactions that occur as ATP is used at a rapid rate.)

Anyway, the point here is that one source of that burning ache during exercise is lactic acid accumulation. This does not explain why it hurts the next morning when you get up, though, because the acid will have been cleaned up by then. That’s a different problem.

One reason for stiffness and soreness is the long term effect of flushing the muscle cell with calcium. During exercise, each contraction is accompanied by a surge of calcium ions, followed by its removal by pumps in the sarcoplasmic reticulum slurping it back up for storage. So exercise consists of a repeated cycle of surge and slurp of calcium ions, and one of the effects is that the increased levels of ions lead to actual physical swelling of the muscle fibers, which can reduce short-term performance. Another effect is that altering the calcium balance of the cell leads to the activation of enzymes that break down and rebuild proteins in the cell. What that does is promote active remodeling of those actin/myosin filaments, construction of new filaments, and growth of the muscle. It hurts because the muscle is under construction and is being physically remodeled, just like your coach probably told you. No pain, no gain.

There’s another reason muscles may hurt a great deal the day after exercise, and that is that you can actually disrupt and damage and even kill muscle fibers, and that certain kinds of exercise are particularly effective at damaging the tissue.

A couple of years ago, I had this brought home personally. Our students have to give a senior seminar in a biology topic of their choice in their last year, before we let them graduate, and one of my students was interested in exercise physiology and knew about this phenomenon of eccentric exercise promoting greater tissue damage. He also knew that it had its most potent effects in naive tissue — muscles can adapt to repeated abuse, and show smaller and smaller responses to this kind of exercise over time. He was an athlete, so it was going to have minimal effect on him, so he looked about for a flabby, lazy, deskbound sort of person to test, and somehow he thought his advisor, me, would be a perfect subject.

Concentric and eccentric exercise are different. Imagine holding a weight in your hand as you sit there, and you contract your biceps to bend your elbow and lift the weight towards your face — imagine drinking a large stein of beer, for instance (it’s exercise, really). The muscle filaments are ratcheting along to contract, and they are shortening the muscle: that is concentric exercise. Now, though, you lower your hand to put the stein back on the table. You don’t simply relax all your muscles and let your arm flop so the stein falls with a crash to the table — it might spill! — instead, the muscle fibers in your biceps are at a low level of activity, the myosin/actin filaments are ratcheting to generate tension, while the muscle is lengthening, rather than shortening. That’s eccentric exercise: some of your muscle fibers are trying to shorten the muscle while the muscle is actually lengthening.

So my student took me to the gym for a relatively easy hour of working out in the weight room, concentrating on eccentric exercise. It wasn’t bad at all, and he kept the workout relatively light, so I never strained myself. So we did things like assisted bench presses, where he would help me raise the weight (the concentric part), and then I would ease it down slowly (the eccentric part). It wasn’t bad at all, I thought, and we did a series of simple exercise to work out different muscle groups.

Then, the next morning, I tried to get up. Aaaaiaiaiaeeeaaargh. His experiment had been spectacularly successful, and I could barely move. Let me tell you, brushing my teeth that day was the most exquisite agony — just raising my hand to my mouth was bad enough, but wiggling my arm gently once I got it there? Forget about it.

So I got to be a prop at his seminar, standing still at the front of the room and occasionally screaming through gritted teeth when he asked me to move in certain ways, while he explained what was going on in my muscles. I had to give him an A for admiration at his fabulously sadomasochistic technique.

So what had I done to my muscles? Forced lengthening of muscles under tension actually causes small tears in the fibers, disrupting the excitation-contraction coupling mechanism. There are tiny membranous tubes running through the muscle fibers called the t-tubule system, which conducts electrical activity at the membrane deep into the interior, where it activates the sarcoplasmic reticulum to release calcium. Those were being torn. That makes the membrane leaky and sensitive, leading to fluid imbalances, and generally making the muscle less responsive until repaired.

Another factor is damage to the filament structure. The peculiar extension while contracting would lead to errors in the alignment of the overlapping parts of the myosin and actin filaments, leading to tangled, disrupted structures that are no longer able to function efficiently, and further contraction could cause physical injury to the fiber, which triggers a pain and inflammation response.

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During an active lengthening, longer, weaker sarcomeres are stretched onto the descending limb of their length-tension relation where they lengthen rapidly, uncontrollably, until they are beyond myofilament overlap and tension in passive structures has halted further lengthening. Repeated overextension of sarcomeres leads to their disruption. Muscle fibres with disrupted sarcomeres in series with still-functioning sarcomeres show a shift in optimum length for tension in the direction of longer muscle lengths. When the region of disruption is large enough it leads to membrane damage. This could be envisaged as a two-stage process, beginning with tearing of t-tubules. Any fall in tension at this point would be reversible with caffeine. It would be followed by damage to the sarcoplasmic reticulum, uncontrolled Ca2+ release from its stores and triggering of a local injury contracture. That, in turn, would raise muscle passive tension. If the damage was extensive enough, parts of the fibre, or the whole fibre, would die. This fall in tension would not be recoverable with caffeine. Breakdown products of dead and dying cells would lead to a local inflammatory response associated with tissue oedema and soreness.

This process actually messes up your muscles. These are electron micrographs of muscle biopsies taken from human subjects who’d been put through the procedure (I drew the line there, and did not let me student stab me with big needles — hadn’t he gotten enough pleasure out of this already — so these aren’t my muscles).

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The control at the top left shows normal, healthy, well-organized muscle fibers; the panel just below it as a sample from muscle immediately after eccentric exercise, which is clearly more disorganized. The three panels labeled “1d” all show muscle one day after eccentric exercise, and all show signs of disruption — look at those z discs, the dark bands in the muscle. They’ve been broken up quite a bit.

If your muscles hurt, though, don’t panic: the panel at the top right is of muscle fibers 14 days after exercise, and they are fully recovered and are once again well-ordered.

So why do your muscles hurt after exercise? There are three major reasons. 1) a transient accumulation of acids produced by ATP hydrolysis that can cause some soreness during exercise. 2) Changes in ion concentrations in the muscle that can cause some fluid swelling, and also triggers active remodeling of the proteins for growth. And 3) you broke ’em. You can cause micro-tears and internal disruption of muscle proteins that can actually force your muscles to throw out and reconstruct whole fibers.

What should you do if your muscles are aching after exercise? Personally, I say just stop it altogether, but that’s just me. For the more active and sensible among you, a better solution would be to reduce the intensity of exercise to light, submaximal exertion and stretching exercises, which have been found to reduce soreness and promote more rapid recovery of muscle tension. Light massage is also good for reducing pain, but hasn’t been found to do much to facilitate actual physical recovery otherwise. I’m all for reducing pain, of course.

As usual, though, if pain worsens or continues for more than a few days, or is particularly intense and localized, get off the internet and SEE A REAL DOCTOR. In the case of my intentionally induced eccentric muscle exercise, the serious pain only lasted for about 3 days, and after a week, felt no after-effects at all.


Proske U, Morgan DL (2001) Muscle damage from eccentric exercise: mechanism, mechanical signs, adaptation, and clinical applications. J Physiol 537(2):333-345.

Where’s the duct tape?

Obviously, I did it all wrong. I have a digital video microscope in my lab, but what I did was spend about $20,000 on a nice microscope, $1000 on a digital still camera and about $500 on a digital video camera, and $200 on a pair of custom adapters to link them together. The principle is simple enough, though; you’re just mounting a camera on the scope where your eye would be and grabbing images with a standard computer interface. So here’s New Scientist bragging about building a video microscope for £15.

I’ve done something similar in the past, but I can one-up Lewis Sykes: I made my adapter with cardboard and duct tape, instead of going all out and fabricating fancy-pants acrylic rings.

I should confess that there is a little bit of a quality difference between the images I get on my lab scope and the ones you can get out of $30 microscope. As long as you’re not trying to resolve sub-micron details, though, you can probably get by.

I shouldn’t have read all those Conan books as a kid

My parents never got me nice things. Sure, there was that one Tony the Tiger cereal bowl we kids all fought over back in the 1960s, but they never got us one of these.

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See? If I’d been born just a little earlier, 14,000 years ago instead of in the 1950s, Dad might have given me the skull of one of his enemies from which to dine on my Chocolate Frosted Sugar Bombs. I was deprived.

This cool paper by Bello, Parfitt, and Stringer describes finds from a cave in Somerset, England which, among many other relics of Upper Paleolithic habitation, included several human skull caps with clear signs of post-mortem modification. My father’s lineage descended from people in that part of the world, so now I’m really miffed — it was an old family tradition, and they just didn’t keep it up.

Anyway, the authors analyzed these curious crania and found cut marks where they’d been defleshed, and percussion marks where the bone had been shaped. They’re fairly thorough in describing the process — it’s almost a how-to — so maybe we’ll get something on Etsy or Make magazine sometime.

The distribution of the cut-marks and percussion damage on the Gough’s Cave cranial sample indicates the skilled post-mortem processing of the head. This included careful removal of soft tissues and controlled percussion. Cut-marks on the areas of insertion of neck muscles and the presence of cut-marks in proximity to the foramen magnum indicate that the head was detached from the body at the base of the skull. This is confirmed by the distribution of cut-marks on the axis and atlas vertebrae, which indicate dismemberment of the neck and head. It is likely that this took place shortly after death, before desiccation of the soft tissues or decomposition and natural disarticulation had occurred. The presence of cut-marks on the areas of insertions of the medial pterygoid muscle (both on the sphenoid and the mandible) indicate subsequent detachment of the mandible from the skull. In the case of the two maxillae, the front teeth showed post-mortem scratches and percussion fractures on the inferior border of their labial surfaces. Although non-masticatory scratches on front teeth are well documented, descriptions of percussion modifications are rare in the literature, making it difficult to interpret their significance. Because of the taphonomic and sedimentological characteristics of the site, it is very unlikely that these modifications were naturally produced by sediment pressure or trampling. Neither can these marks be attributed to post-excavation cleaning or instrument damage. If associated with the processing of the head, it is possible that scratches and breakages were induced by a lever inserted between the occlusal plane of the front teeth, in order to disjoint and separate upper and lower jaws. The distribution of cut-marks on the temporal, sphenoid, parietal and zygomatic bones indicate removal of the major muscles of the skull (masseter and temporalis). The location of cut-marks in discrete areas such as the lingual surface of the mandible, the alveolar process of the maxilla, the root of the zygomatic process on the temporal bone and along the fronto-nasal suture, indicates that the tongue, lips, ears, and nose were also removed. Cut-marks around and inside the eye sockets and on the malar fossae of the maxilla suggest extraction of the eyes and cheeks. Finally, the high incidence of oblique para-sagittal cut-marks on the vault, in areas far from the attachment of muscles, on the squama of the frontal and on the parietals on both sides of the sagittal suture, suggests scalp removal. All these modifications are indicative of meticulous removal of the soft tissues covering the skull. The final stage in the sequence of alterations involved controlled percussion resulting in a systematic pattern of removal of the facial bones and the cranial base with minimum breakage of the vault. The distribution of impact damage and flaking is indicative of carefully controlled chipping of the broken edges in order to make them more regular.

Well, I’m going to go have my breakfast now. In a plain old boring ceramic bowl. You know, this heart-healthy diet I’m on would have a little more pizazz if it were served properly…just a hint.

A physicist agrees with me!

So I guess they can’t be all bad. Yesterday, I chastised Michio Kaku severely for stepping out of his expertise as a physicist to say something stupid about biology. James Kakalios agreed with me, and sent along a little essay about the subject that also makes the point that expertise is important.

In Defense of Elites

James Kakalios

Following the recent mid-term elections, the consensus of many pundits is that this past November the American public sent a strong message of “anti-elitism.” The good news is that nothing could be further from the truth.

Americans are certainly not anti-elite, nor are they anti-intellectual. Everyone, after all, wants their doctor, lawyer, or auto-mechanic to be an expert in their field. Few would willingly choose a brain surgeon who was at the bottom of their graduating class, no matter how much fun they may be to share a beer with.

However, Americans are anti-snobbery and have no patience for those whose insecurity compels them to tell us why we’re “wrong” to like what we do, whether it’s NASCAR, fantasy baseball, comic books or Star Wars (OK, the critics may have a point about Episode II: Attack of the Clones). Given the demands of the ever-expanding modern work-week (forget about the jetpack, what I want to know is where’s my four hour work week that was similarly promised to be here in the 21st century!), it is no wonder that that many Americans might devote their limited free time to learning the starting nine players of their local baseball team rather than the nine justices on the Supreme Court.

But there is a real issue that goes beyond a lack of free time. Nearly every week brings another news story of the low regard in which the general public holds intellectuals and scientists. From doubting claims of climatologists concerning the source of changes in the Earth’s average temperature, to persistent attempts by some local school boards to sabotage their children’s education of the principles of Darwinian evolution, the view of many seems to be that “science is just another opinion.”

As a physics professor who is also an avid reader of comic books, I know that it was not always so. Back in the 1950’s and 1960’s, superhero comic books reflected the popular zeitgist and, whether the planet was threatened by invaders from planet X or superpowered master villains, it was typically a scientist that saved the day. Science fiction comic books whose stories took place in the future (sometimes all the way in the year 2000!) often promised that we would live in a gleaming utopia brought to us by scientific advancements.

And in many ways the comic books have been proven correct. Diseases and ailments that were fatal just a few generations ago can now be easily treated, we can peer into the body without the cut of a knife using Magnetic Resonance Imaging, there are few points on the globe that can not be reached by wireless communication, and the computing power of a laptop exceeds that of room-size calculating machines that represented the state of the art in 1950. All brought to us through the efforts of elites.

And this is where the current distrust of scientists becomes a major concern. For there are real problems that need to be addressed, but we can’t handle them without the advice of experts, which are often not respected by both the general public and the scientific community.

The findings and conclusions of scientists and engineers who have devoted years and years to the mastery of their fields of inquiry should be accorded the respect they deserve, and not dismissed for ideological reasons. Few people second-guess the political motivations of their dentist when informed that they have a cavity – why would they do the same with atmospheric scientists when they discuss a hole in the ozone layer? Strong science, elaborated by experts, is the foundation for sound policy.

What happens when experts disagree? More good news — this happens much less than one might think, at least concerning questions of fact (interpretations are another matter). Of course, it is important to realize that not every scientist is an expert in every branch of science (I am concerned here with scientific communication, and not interdisciplinary research). If my cardiologist tells me that I need open heart surgery, I may seek a second opinion before having a difficult and expensive operation — but I won’t consult a dermatologist.

It pains me to say this, but — physics professors are not experts in all fields of science. While we may be able to address, for example, the quantum mechanical mechanisms by which carbon dioxide ignores visible light but absorbs and re—emits infra—red radiation, and can discuss the application of the scientific method, we are not climatologists, and should respect the conclusions of those who have devoted the same time and effort to their field as we have to ours. As the science fiction author Robert Heinlein wrote: “Expertise in one field does not carry over into other fields. But experts often think so. The narrower their field of knowledge the more likely they are to think so.”

Most couples therapists will tell you — miscommunication is a two-way street. Scientists and the general public need to stop talking past each other, so that we can all benefit from the counsel of elite experts. For the problems that we as a nation face are as serious as a heart attack!

James Kakalios is the Taylor Distinguished Professor in the School of Physics and Astronomy at the University of Minnesota, and the author of The Amazing Story of Quantum Mechanics (Gotham, 2010).

Buying science

This week’s Nature has a substantial and fairly even-handed article on the unease Templeton funding causes. Jerry Coyne is prominently featured, so you know it isn’t an entirely friendly review.

Religion is based on dogma and belief, whereas science is based on doubt and questioning,” says Coyne, echoing an argument made by many others. “In religion, faith is a virtue. In science, faith is a vice.” The purpose of the Templeton Foundation is to break down that wall, he says — to reconcile the irreconcilable and give religion scholarly legitimacy.

They also quote scientists who found the Templeton Foundation fairly open and tolerant of results that were not supportive of their prejudices…but I still don’t trust them. They’re busy putting on a show of open-mindedness, and they are staffed by some competent and politically savvy people, and they know that a few Potemkin scientists with contrary results will help in their overall goal of counterfeiting scientific credibility for their religious cause.

This is especially pressing now as Republicans strain to cut science funding — do we really want American science to become increasingly reliant on funding from organizations with an agenda?

How can so many farm state politicians fail to understand the phrase “seed corn”?

Paul Krugman has a lovely phrase to describe Republican policies: Eat the future. They are under pressure to cut spending, any spending, but they refuse to touch anything that might cause immediate pain to the electorate…so instead, anything in the budget that affects future voters is going to get the axe.

Once you understand the imperatives Republicans face, however, it all makes sense. By slashing future-oriented programs, they can deliver the instant spending cuts Tea Partiers demand, without imposing too much immediate pain on voters. And as for the future costs — a population damaged by childhood malnutrition, an increased chance of terrorist attacks, a revenue system undermined by widespread tax evasion — well, tomorrow is another day.

He could have mentioned a few other areas that can be cut, like education, and especially science. Republican voters don’t understand science, they don’t support science, so if there’s anything in the budget that makes Republican politicians salivate in a hungry, predatory way, it’s science. So you won’t be surprised at the prospects for the NIH.

Dear Colleague,

For months the new House leadership has been promising to cut billions in federal funding in fiscal year (FY) 2011. Later this week the House will try to make the rhetoric a reality by voting on HR 1, a “continuing resolution” (CR) that would cut NIH funding by $1.6 billion (5.2%) BELOW the current level – reducing the budget for medical research to $29.4 billion!

We must rally everyone – researchers, trainees, lab personnel – in the scientific community to protest these draconian cuts. Please go to [this link] for instructions on how to call your Representative’s Washington, DC office today! Urge him/her to oppose the cuts to NIH and vote against HR 1. Once you’ve made the call, let us know how it went by sending a short email to the address provided in the call instructions and forward the alert link to your colleagues. We must explain to our Representatives how cuts to NIH will have a devastating impact on their constituents!

Sincerely,

William T. Talman, MD
FASEB President

The cannibals are out there, and they don’t look like you might expect: they wear nice suits and dresses, and they go to church every week, and they are fervent in their patriotism. But they’re planning to eat the future, anyway.

Guinea pigs, please line up here

I have received a request for volunteers to assist as subjects in a research project. I was disappointed; there are no exotic drugs, no catheters, no insane experimental surgeries that will turn you into a super-being with surprising powers beyond all mortal ken, but the fellow did manage to spell my name correctly, so it must be on the up-and-up. Contact Ben Myers (hey! That’s how he got the spelling correct — he cheated!) if you’re interested.

Dr. Myers,

I am an assistant professor of communication studies at USC Upstate. I am in the process of starting a research project and I was wondering if I could ask you for a favor. My research project is centered around atheist/agnostic coming out experiences. For my data, I am planning on collecting stories from those who have “come out” to religious family and friends. I am an ally (and a big fan of your blog). I am interested in this project because of my own very difficult “coming out” experience with my family.
I am planning on doing a rhetorical analysis of common themes across coming out stories. I have included my research plan if you would like more details. Also, I have already received IRB approval for the study.
I will conduct and record interviews over skype. The interviews are open-ended, so I have a few basic questions but I am primarily interested in just letting people tell their stories.
To start the project, I need to find atheists/agnostics who would be willing to share their “coming out” stories. This is where I would like to ask you a favor. I am looking not just for atheist/agnostics, but for atheists/agnostics who have specific “coming out” stories. I am sure there are lots of readers of Pharyngula who would fit the criteria. Would you be willing to dedicate a post to helping me find participants? Perhaps you could post my email and a short blurb about what the research project is about. Participants could then contact me directly.
Also, no need to worry about the project. Any work that results from these interviews will be presented with the ethos of helping readers understand the “coming out” process and how difficult it is. I am an ally, and a proud “out” atheist myself.
Thank you very much for your consideration. And please do not hesitate to ask for additional information if you feel it necessary. And keep on fighting the good fight.

Sincerely,

Ben


W. Benjamin Myers, Ph.D.
Assistant Professor of Speech
Department of Fine Arts and Communication Studies
USC Upstate
864.503.5870

Here’s the short research plan.

I have annoyed Jesse Bering

That’s what I do, after all. I strongly criticized his uncritical analysis of a set of rape-related evolutionary psychology studies, and now he responds with a rebuttal. It’s not a very good rebuttal, but I highly recommend his second paragraph in which he lists a good collection of links to several people who also ripped into his article. That part is excellent!

But then let’s get into the part where he argues with me.

P.Z. Myers is not, of course, the undisputed public ambassador of his discipline (although I’ve no doubt he sees himself as such), and by no means does the following apply to all biologists, or even all those who are critical of evolutionary psychology. But Myers’ affect-laden views regarding evolutionary psychology do represent those of at least a significant and vocal minority.

Not an auspicious start to accuse me of regarding myself as “the undisputed public ambassador of” biology, which certainly isn’t the case. This is a blog written by a professor in a small town in rural Minnesota. I’m kind of aware of exactly what it is, and lack the airs Bering wants to assign to me. But then, this isn’t surprising, since most of his following arguments rely on telling me what I intended, and he also gets that wrong. Except this little bit, where he does get the overall objections right.

Critics are particularly irritated by the fact that evolutionary psychologists do not test for genetic inheritance of the very traits they argue are adaptive but instead rely on behavioral or self-report measures to evaluate their theories. They also believe that evolutionary psychologists take too many story-telling liberties in reconstructing the ancestral past, since we can never know for certain what life was like hundreds of thousands of years ago, when such traits would have, theoretically, been favored by natural selection. (This is a point also stressed by Rennie in his critique of my Slate essay.) According to Myers, the whole messy endeavor, therefore, “is a teetering pyramid of stacked ‘couldas’ and guesses that it woulda had an influence on evolution.”

This is actually a reasonable summary of my general disagreements with evolutionary psychology. They are quite fond of inventing evolutionary stories about phenomena that don’t even have an iota of evidence for being genetic, and can come up with truly awesome causal accounts for even the most trivial observations.

He picks out one of my objections to argue why the evolutionary psychology crowd can’t do one of the experiments I didn’t suggest doing, which is a little odd, but OK.

In his post, Myers uses my discussion of the evolution of the human penis as a prime example of the sloppy work being done in the study of evolution and human behavior. He pillories psychologist Gordon Gallup’s famous “dildo study,” which suggests that the distinctive mushroom-capped shape of the penis might serve to scoop a competitor’s semen out of the vagina. (I described this work at long, intimate length in two prior articles in Scientific American.) Myers calls this penis study “tripe” because Gallup and his colleagues failed to show how variations in penis shape within a population–and variations in how the penis is used for coital thrusting–directly affect fertilization rates. Instead, the researchers relied on dildos of different designs, surveys of college students’ detailing their sexual behaviors, and a batch of artificial semen.

Now, I can only assume that Myers has not had to face a university human-research ethics committee in the past several decades. If he had, he would realize that his suggested empirical approach would be unilaterally rejected by these conservative bureaucratic gatekeepers. Does Myers really believe that these seasoned investigators wouldn’t rather have done the full experiment he describes–if only they lived in a less prudish and libellous university world? The fact of the matter is that research psychologists studying human sexuality are hamstrung by necessary ethical constraints when designing their studies. Perhaps Myers would be happy enough to allow investigators into his bedroom to examine the precise depth and vigor to which he plunges into his wife’s vaginal canal after they’ve been separated for a week, but most couples would be a tad more reticent. Gallup’s dildo study, and his related work on penis evolution, offered an ingenious–ingenious–way to get around some very real practical and ethical limitations. Is it perfect? No. Again, the perfect study, conceptually speaking, is often the least ethical one, at least as deemed by research ethics committees. But was it driven by clear, testable, evolutionary hypotheses? Yes. And it offered useful information that was otherwise unknown.

Telling me that they can’t do an experiment that I didn’t suggest doing doesn’t really undermine anything I said. I’m perfectly aware of the ethical limitations of human research, which is one reason why I work on animal models. The problem is that what I actually offered as shortcomings of the work wasn’t their failure to wire up my genitals, but this:

They don’t have any evidence that this behavior actually affects the fertilization rate of one partner’s sperm over another, they don’t have any indication of morphological differences in human populations that make some individuals better semen-scoopers, they don’t have any evidence that this behavior has had a differential effect in human history.

Those are the criteria I would expect to see met in order to discuss this issue as an evolutionary problem; what Bering’s sources were studying were mechanical and physiological aspects of some plumbing (which can be interesting!), and then tacking on unwarranted conclusions about evolutionary history. In fact, I don’t see how Bering’s strange and unexecutable experiment of logging the details of my personal sexual behavior would even touch my evolutionary objections.

He also skips over another relevant point I emphasized. I read the research papers he cited. These were studies that had him “riveted, and convinced”, but when I looked at, for instance, the study that found an increase in women’s handgrip strength during ovulation, the paper itself mentioned that there were many other studies that showed no variation in strength over the menstrual cycle. Which is it? Do you just pick the result that favors your interpretation?

Jerry Coyne has a summary of reactions, too, and mentions several instances where the papers aren’t as clear in their support of the evo-psych hypotheses as is claimed. These are very noisy data that sometimes support and sometimes contradict their claims, and it seems that whatever result they pluck out of the mess, it’s always in support of some purported evolutionarily significant effect on behavior or physiology.

As I said in my previous article, I think the general claim of evolutionary psychology, that our current behavior has been shaped by our biological history, is true. I think much of the research in the field is damaging to their thesis, though, not because it demonstrates the opposite, but because it flits over tiny details, like monthly variations in how a woman moves her hips or how she feels about men, and pretends that they’re all examples of the power of natural selection in sculpting a genome that encodes every pelvic wobble and every nerve impulse. It’s become a kind of modern ornithomancy, where each dip and swirl and change in direction of a flight of birds is interpreted as directly connected to the fate of nations. I remain unconvinced.

What tool would you put in your cognitive toolkit?

The Edge annual question and its answers are out. This year, John Brockman asked, “What scientific concept would improve everybody’s cognitive toolkit?” He got 158 people to send in answers.

I was one of them. If you like my answer, you might also like Sean Carroll’s and Carl Zimmer’s — we seem to have made similar points. Carl has a thread on the topic, and so does Sean: I think I like his original title of dysteleological physicalism better, never mind Carl’s post deploring jargon.