Laughter Is OK Medicine, Unless It Kills You

Careful with the bedside banter, doctors. Before you put on your best Patch Adams impression, you might want to consider whether your attempts at humor will ease your patient's discomfort or give him a protruding hernia.

That's the conclusion of a review paper in the Christmas issue of BMJ that asks the jolly question of whether laughter can kill. The two authors, R. E. Ferner of the University of Birmingham and J. K. Aronson of Oxford University—no JK-ing, those are his real initials—take a tongue-in-cheek approach. They even give their research question an acronym: MIRTH (Methodical Investigation of Risibility, Therapeutic and Harmful).

Ferner and Aronson scoured medical literature for studies having to do with laughter. After "excluding papers on the Caribbean sponge Prosuberites laughlini and with authors called Laughing, Laughter, Laughton, or McLaughlin," they were left with three categories of study. One had to do with the benefits of laughter, one with its dangers, and the third with medical conditions that have laughter as a symptom.

Let's hear the bad news first. Laughter, according to various researchers, can lead to syncope (fainting), arrhythmia, and cardiac rupture. In asthmatics, laughing can trigger an attack. Laughing can even cause pneumothorax, a collapsed lung. People with cataplexy, a rare condition tied to narcolepsy, may suddenly lose all their muscle strength and collapse during a fit of laughter. An especially good laugh can make a person's hernia protrude, or dislocate someone's jaw.

Among the more pedestrian dangers, breathing in sharply when you start to laugh can make you choke. Laughing in someone's face can spread germs. And, of course, there's the danger of pee coming out when you laugh, which doctors call "giggle incontinence."

The authors also gathered a list of about three dozen medical conditions that have been reported—commonly or not—to cause laughter. These include epilepsy, brain tumors, multiple sclerosis, and kuru (a disease you are unlikely to contract unless you're a practicing cannibal).

Now for the good news. Laughter may increase your pain tolerance, reduce stiffness in the walls of your arteries, and even lower your risk of a heart attack. In patients with chronic obstructive pulmonary disease (COPD), laughter can improve lung function. Fifteen minutes of laughter reportedly burns 40 calories, which fitness-wise makes it similar to a very slow walk (or, according to Fitness magazine, barbecuing.)

Most strangely, one study used clowns to try to (indirectly) get women pregnant. Immediately after undergoing IVF, women were subjected to 12 to 15 minutes of entertainment by "a clown, dressed as a chef de cuisine." Among these women, 36 percent became pregnant, compared to just 20 percent in a control group.

Perhaps aspiring clowns themselves, the authors can't resist throwing in a few puns of their own: "Laughing fit to burst can cause cardiac rupture." "Perhaps surgical patients derive no advantage from being in stitches." "It remains to be seen whether...sick jokes make you ill, [or] dry wit causes dehydration." I'll give them the benefit of the doubt and assume that, knowing the potentially serious side effects of laughter, they chose to spare their audience the risk.


Image: Urban Combing (Ultrastar175g) (via Flickr)

R E Ferner, & J K Aronson (2013). Laughter and MIRTH (Methodical Investigation of Risibility, Therapeutic and Harmful): narrative synthesis. BMJ DOI: 10.1136/bmj.f7274

Hack Your Workout: These Songs Make People Take Bigger Steps

Do you have a workout playlist? You may find yourself matching the stride of your power walk to the beat in your earbuds—but tempo isn't the only thing affecting how fast you go. Certain musical pieces seem to make people take longer strides, even while walking to the same beat. (Spoiler alert: Aqua.)

Marc Leman is a musicologist at Ghent University in Belgium. With his colleagues, he created a list of 52 songs with a tempo of 130 beats per minute, a speed they chose based on previous research. The playlist included a variety of genres, and all the songs were in 4/4 time.

Then the researchers gathered 18 "normally built" adults, strapped sensors to their legs, and sent them walking laps around a gymnasium. The subjects were explicitly told to walk in time to the beat of the music. Through headphones, they heard 30-second clips of the different songs, with periodic interludes of only a metronome sound.

Although all the music had the same tempo of 130 beats per minute—which subjects stepped in time with—their actual walking speed varied as they took longer or shorter strides. Leman says that to certain songs, people walked 10 percent faster than they did to others (or to the metronome beat).

The researchers dubbed the fastest-walking songs "activating," and the songs that made people walk slowest "relaxing." The full playlist is here, ranked from most relaxing to most activating. These were the top 10 most relaxing songs, to which walkers made the least forward progress:

And here are the tunes to which people covered the most ground:

Right around the middle was "Dragostea din tei," better known by some as "the Numa Numa song." Test subjects probably got slowed down by the requisite arm flailing.

Separately, the researchers asked subjects to rate the musical selections on a variety of adjectives: Was the song happy or sad? Tender or aggressive? Known or unknown to the listener?

Some of the responses were tied to how speedily the songs made them walk. For example, pieces described as "stuttering" rather than "flowing" made people take shorter strides. Pieces that subjects found especially "aggressive" or "loud" (although the volumes of all the songs had been matched in their headphones) made people walk faster. So did songs they described as "bad" rather than "good." (This may explain "Barbie Girl").

The musicologists, meanwhile, tried to find more scientific explanations for the powers of certain songs. Leman says this was surprisingly difficult. They did find that more activating songs tended to have simpler melodies, with fewer notes per beat. These pieces often had a strong bass line, as well as clear downbeats ("one two three four..."). The group is still working on figuring out what kinds of music make people move the fastest.

For his own exercise playlist, Leman is a fan of jazz, though he says it's not always great at getting a person moving. He thinks syncopation, which interrupts the regular beat of the music, is an important factor in making a piece relaxing rather than activating. Instead of marching straight ahead, syncopated jazz music seems to encourage you to walk with more horizontal motion, Leman says: "You want to swing."


Image: by Malingering (via Flickr)

Marc Leman, Dirk Moelants, Matthias Varewyck, Frederik Styns, Leon van Noorden, & Jean-Pierre Martens (2013). Activating and Relaxing Music Entrains the Speed of Beat Synchronized Walking PLOS ONE DOI: 10.1371/journal.pone.0067932

Ants Reveal How to Build a Tunnel You Can't Fall Down

It's hard to keep your footing in a steep tunnel made of loose dirt while others are scrambling around and over your body. Harder still in pitch blackness. That's why fire ants build tunnels that will catch them when they fall—a strategy human engineers might want to steal.

"Slips and missteps are likely a constant, recurring feature of life underground," says Nick Gravish, a graduate student in Daniel Goldman's rheology and biomechanics lab at Georgia Tech. Yet ants have to traverse their tunnels quickly, especially when there's a colony emergency like a flood or destruction by a gardener's spade.

To study how ants engineer their tunnels, Gravish brought the fire ant Solenopsis invicta into the lab. Invasive to countries around the world and packing a nasty sting, these South American ants deal out plenty of hardship. But Gravish was interested in how they handle adversity themselves.

First, the ants were put into "laboratory soil" (actually tiny glass balls) to dig. Researchers took x-ray CT scans of the resulting tunnels and found that no matter the moisture of the "soil" or the size of the glass beads, ants dug circular tunnels of approximately the same diameter. That diameter was just a little bit more than the length of their bodies, not counting legs or antennae.

This suggested that the diameter of the tunnel was crucial to the fire ants. To see how well the ants moved within these tunnels, the researchers recorded video of them climbing as fast as they could. ("We startled them into climbing at high speed by exhaling gently into the nest," Gravish says.) They saw that ants were able to navigate their tunnels quickly, reaching speeds of more than 9 body lengths per second. They also saw that sometimes the ants slipped and had to recover their footing.

In addition to their tunnels, the researchers recorded ants climbing in vertical glass tubes. To get a better idea of how ants corrected their falls, the scientists jolted the tubes to knock the ants off the walls while they were climbing. (If you enjoy videos in the falling-bugs genre, this study generated several new additions. Here's one video of several ants falling and stopping themselves.)

Now the reason ants build tunnels so close in diameter to their own body length became clear. Ants responded to a fall by spreading all their appendages wide and waiting until they jammed to a stop. "One of the coolest things we found was that fire ants used their antennae to brace themselves," Gravish says. While falling, the ants turned these delicate sensors into extra load-bearing limbs.

When the glass tube width increased to 1.3 times the ants' body length, the strategy began to fail. The tunnels ants built themselves had an average diameter of just 1.06 times their body length, the authors report in PNAS. It seems fire ants put most of the responsibility for stopping falls on the tunnels themselves. After that, all a plummeting insect has to do is stretch out its limbs.

Gravish likens this strategy to the way humans build stairs. Steps are engineered to fit our bodies. If they're too tall or short, we struggle to use them (or maybe just fall down them). But with the right design, our environment works with us to get us where we're going.

This strategy could inspire how we design robots for confined spaces such as search-and-rescue zones, Gravish says. For instance, "falling is usually considered a failure mode for a robot." But fire ants seem to use little falls to descend more quickly through their tunnels. If engineers knew the size of the cracks and crevices in a disaster area, they might be able to send in many inexpensive robots designed to tumble through those spaces—rather than one very expensive robot built to keep its footing.

What about humans ourselves: would we benefit from building tunnels that were only as wide as our head-plus-torso length, like the ants? Gravish points out that fire ants often fall many body lengths before catching themselves, making this not such a great strategy for people. "Ants have a robust exoskeleton," he says. "We humans are quite soft in comparison."


Images: ant in tunnel by Laura Danielle Wagner; ants falling by Gravish et al.

Gravish, N., Monaenkova, D., Goodisman, M., & Goldman, D. (2013). Climbing, falling, and jamming during ant locomotion in confined environments Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1302428110

From Mastiff to Miniature Poodle, Dogs Know Each Other by Sight

Anyone who's walked a dog and seen it spring to attention when another dogs rounds a corner—even though that animal is still a full block away—may have wondered how exactly dogs recognize each other. What makes a golden retriever perk up its ears and wag its tail at an approaching greyhound but not, say, a stroller? Why does it ever occur to a dachshund to play with a pit bull in the park? Why don't average-sized dogs chase toy breeds away as if they were squirrels?

You might assume dogs, with their powerful noses, are getting an advantage from scent. Perhaps dog breeds all smell the same, despite looking wildly different. A new study, though, shows that dogs can find each other by sight alone. Dogs are able to spot another dog, no matter the breed, from among a crowd of other animals. Scientists don't know how they do it.

Since other animals such as sheep, macaques, and cows have shown in the lab that they can recognize their peers by sight, scientists in France asked whether dogs could do this when challenged with a full complement of breeds. To understand the magnitude of the problem a dog faces, consider that there are 400 to 500 registered dog breeds. Dogs are more diverse than any other animal species on Earth. Furthermore, their vision isn't that great. If Fido wants to find a mate, though, he'd better know the difference between a Pomeranian and a fluffy cat.

Bertrand Deputte of the National Veterinary School at Alfort, France, and his coauthors recruited nine dogs for their study. All the dogs were pets owned by veterinary students. They were a mix of male and female, and mostly mixed-breeds.

In each stage of the experiment, a dog sat facing two screens on tables while a human stood behind it. (The human experimenter, to make absolutely sure he didn't give any hints, stood motionless and wore dark glasses.) On the experimenter's command, the dog walked forward and chose one of the two screens by placing its paw on a table.

Choosing the correct picture got the dog a food reward. But what was "correct" shifted over the course of the experiment, as the researchers took the dogs through a series of challenges.

In early sessions, dogs won a treat if they chose a screen showing a dog's face over an empty screen. They they had to choose a dog's face over a cow's face, where the dog and cow were the same every time but kept swapping screens. Then the dogs had to generalize: the screens showed dog and cow faces the subjects hadn't seen before, and they had to choose the dog. 

At last came the main challenge: dogs versus everything else. One screen showed a dog's face (a different dog every time) and the other showed some non-dog species (cow, cat, rabbit, human, bird, and so on). Every picture was zoomed in on the animal's head, so that the canine subjects couldn't get any clues from body size or shape—not to mention movement, sound, or smell. Some faces were shown straight on; others were in profile or three-quarters view. Nevertheless, every dog in the experiment succeeded.

"We were rather surprised by the ease dogs had," Deputte says, "in spite of huge variability of dog breeds and the variety of animal and humans faces that constituted the other category." All nine dogs, once they'd learned what the human experimenter wanted, could consistently pick out the dog faces on the screens.

To prove the dogs really knew their stuff, researchers also reversed the task and had dogs pick out the picture that wasn't a dog. They aced this test too.

"We couldn't tell how the dogs succeeded" at grouping dog faces from various breeds and different angles all into one category, Deputte says. He believes his results show that dogs have a "concept of dog." Somehow, our pets know immediately whether the animal walking toward them is dog or not-dog. Along with knowing when to sniff the approaching animal's rear end, this may be a power we hopeless humans will never understand.


Autier-Dérian D, Deputte BL, Chalvet-Monfray K, Coulon M, & Mounier L (2013). Visual discrimination of species in dogs (Canis familiaris). Animal cognition PMID: 23404258

Images: George Thomas (Flickr); Dominique Autier-Dérian/Animal Cognition

UPDATE: Bertrand Deputte has clarified that his coauthor Dominique Autier-Dérian did the experimental work for this study.

This Penguin: An Unexpected Journey

The humble king penguin chick had no way of knowing, when it woke up that day, that tall creatures from far away would come to send it on a journey. Nor could it know that its journey would become the subject of a manuscript read and studied by many. (It still doesn't know that part, because it's a bird.) 

When the humans came, the penguin was in its crèche, a cluster of young birds left behind while their parents foraged. Other penguins young and old stretched away from it in all directions. All at once, the chick was lifted from the ground by a pair of human hands. A cloth hood was pulled over its head. The researcher spun the bird around three times, then set off, carrying the bird away from the colony at a fast clip. 

Human and penguin traveled a circuitous route meant to further disorient the bird. When they reached their destination, the human spun the penguin three more times. Finally the chick found itself on solid ground, the hood pulled away from its eyes. Its colony was nowhere in sight.

The penguin was standing inside a circular arena about 10 meters across, surrounded by a meter-high wall of cloth. A scientist quickly fitted a pair of pads, like earmuffs, over the chick's head, deadening the sounds it heard. Then the penguin was left alone.

For fifteen minutes, following cues in its head that were inscrutable to the human observers, the penguin wandered inside the arena. Its instincts told it to return to the crèche right away, so its parents could find it when they came back. While it tried to discover the right direction, human eyes watched and recorded. Finally the walls of the arena came down; the bird was free to go.

It set off waddling across the frozen ground, still wearing its earmuffs. The bird was less than 200 meters from the colony but still couldn't see it. The ocean, though, was in sight. The chick walked straight to the shore. Then it hung a left and headed, correctly, for its colony. Finally it reached the crèche and the other chicks it had left behind. A piece of wood was on the ground, left by the human to mark the spot where the penguin had stood before its abduction.

This traveler was only one of many young penguins the humans lifted from their crèches in those days. Some, instead of earmuffs, had magnets temporarily attached to the backs of their heads. Some were made to travel by night. Some heard a recording of the colony broadcast loudly from speakers within the arena.

The researchers, who came from the University of Oxford and the CEFE in France, hoped to learn from the journeying birds the secrets of penguin navigation. Earlier visits to penguin crèches had told them that the young birds navigate partly by sight, but that most of them could still find their way in the dark—so some other talent was at work too.

Chicks with magnets on their heads did not fare any worse than usual. This revealed to the humans that the penguins didn't rely on sensing the earth's magnetic fields (as homing pigeons are able to do). 

The 18 earmuffed birds were also just as likely to navigate home as non-earmuffed birds. But out of the 16 who made it home without help, researchers noticed that 6 took an unusual path. Like our hero, they seemed to orient themselves by first walking to the ocean, then following it back. It was an intriguing hint that the earmuffs, which quieted the sound of the squawking penguin colony but didn't block it out entirely, were changing the birds' navigation strategy.

The second experiment involving sound truly befuddled the young birds. When speakers inside the arena played the sounds of the colony, almost all the penguins oriented themselves toward the speakers instead of toward home (in the opposite direction). Several chicks stood in front of the speakers, calling to them plaintively.

Five minutes after the walls came down, nearly all the undisturbed chicks were well on their way back to the colony. But many of the chicks who had heard the speaker noises lingered close to the arena. A few set off in the wrong direction entirely. 

The humans made sure all the young birds made it back to their crèches in the end. Afterward, lead author Anna Nesterova told the tale of the traveling penguins in the Journal of Experimental Biology.

From her story, Nesterova drew the moral that penguins use acoustic cues as part of their navigational toolkit. The sound of the distant colony seems to call them back. But the visual landmarks around the birds are also important, and there may be other clues they take in as well. 

As adults, king penguins must navigate between the colony (which may span several kilometers) and their foraging grounds. Upon returning to the colony, they find their partners and chicks by calling out and listening for the right voices among thousands—a task that would seem to require magic. Someday, we meddling humans may learn the secret of how these birds get there and back again.

Nesterova, A., Chiffard, J., Couchoux, C., & Bonadonna, F. (2013). The invisible cues that guide king penguin chicks home. The use of magnetic and acoustic cues during orientation and short-range navigation Journal of Experimental Biology DOI: 10.1242/jeb.075564

Images courtesy of Anna Nesterova.

Why Humans Prefer Not to Gallop

As kids, we discover that our two legs can manage many different gaits. After walking and running we figure out how to tiptoe, hop, and skip. (Personally, I decided at one point to become a better skipper than anyone I knew, practicing backward skipping and figure-eights in our driveway. I may have sensed that my competition in this pursuit was not very stiff.)

For basic getting around, we usually settle on walking and running. But why do we ignore so much of our bipedal repertoire in favor of locomotion that's more, well, pedestrian? Researchers in Belgium asked this question about one gait in particular: the gallop.

In case you missed this one as a kid, the human version of a gallop involves holding one leg always in front of the body and the other leg always behind. Bounding along, you create an uneven rhythm of footfalls: ba-DUM, ba-DUM, ba-DUM.

"Gallop is, though rarely used, a familiar gait for humans," the authors write in the Journal of Experimental Biology. People may start galloping spontaneously under certain (infrequent) circumstances, such as going quickly downhill.

For their study, lead author Pieter Fiers of the University of Antwerp and his colleagues had a dozen volunteers run and gallop down a hallway, then dissected their motion in great detail. Platforms that lined the hallway measured the force people produced in their steps. The subjects were covered in motion-capture markers, like Avatar actors. Finally, a separate group of subjects did their running and galloping on a treadmill while the researchers measured how much oxygen they used and carbon dioxide they gave off.

People preferred to gallop at pretty much the same speed they ran. But the length of a galloping stride was shorter than a running stride—so gallopers had to take more steps, and do more work, to travel at the same speed as runners.

Gallopers exerted that effort unevenly, with the front leg doing more work than the back leg. And the galloping stride, researchers saw, demanded more from the hips than running did. This tired people out quickly. Out of 12 treadmill gallopers in the study, 4 gave up before the end of their 4-minute session, complaining of fatigue and stress in their hips and thighs. (An intended 13th galloper couldn't figure out how to gallop on the treadmill belt in the first place.)

When researchers calculated their subjects' metabolic rates, they found that galloping was about 24% more costly than running at the same speed. In other words, galloping burns up more energy, takes more effort, and is less comfortable than running. It's no wonder we don't usually opt for it.

Still, the fact that we're not efficient at galloping means it would be a tougher workout than running. Maybe athletes should start mixing some alternative gaits into their usual exercise routines. Who knows—with practice, you might become the best galloper in the whole world.


Fiers P, De Clercq D, Segers V, & Aerts P (2012). Biomechanics of human bipedal gallop: asymmetry dictates leg functions. The Journal of experimental biology PMID: 23239890

Image: Devon D'Ewart (Flickr)

12 Days of Inkfish, Day 5: Running on Water

Human courtship rituals—if you believe television commercials, anyway—are lame. The guy who kneels down right at the jewelry store counter ("It fits perfectly!" "Well honey, that's because I already had it sized") has nothing on birds who walk on water for each other.

Grebes are diving waterbirds that live in the Americas and Eurasia. To pair off, they follow an elaborate courtship choreography that includes trading bits of food and mimicking each other's motions. In the ritual's conclusion, both birds suddenly haul their ungainly bodies out of the water and run together on its surface. The grace of the birds and the physics of the maneuver both seem impossible.

You can see a pair of Clark's grebes do their courtship dance in this incredible video from the BBC. Jewelry companies, take note: there's no prelude to romance quite like swallowing a live fish.

Image: screen grab from BBC Life: Birds: Partners for Life

Monitoring from Space Shows Even This Giant Crab Can Navigate Better than You

It was crabnapping for a just cause. But the crustaceans that found themselves suddenly plucked from their burrows, stuffed into opaque sacks, and carried off through the forest couldn't know that. When the scientists freed their captives, they waited to see whether the crabs would find their way home or be stranded forever. They'd be watching—from space.

The best way to find out exactly where and how far an animal travels is to tag it with a GPS tracker. But if you're interested in invertebrates, most of your subjects are too small or squishable to carry around such a device. Enter (scuttling in from stage left) the robber crab, Birgus latro. Also called the coconut crab because of its predilection for cracking open coconuts, the species is the largest arthropod on land. Legs included, it can grow to nearly a meter across.

Robber crabs live on islands in the Indian and Pacific Oceans, tucking themselves into hollow trees and rock crevices during the day to keep their shell-less bodies from drying out. Females make an annual migration to the coast to lay their eggs in the ocean. Less is known, though, about the movements of male crabs. To find out what they're up to—and because the heavier males presumably wouldn't mind the bulky GPS tags so much—Jakob Krieger of the University of Greifswald and other German researchers tagged 55 male robber crabs on Christmas Island.

During the day, the GPS satellites didn't return much data, since the crabs were mostly hidden in their burrows. At night, they began to roam.

The crabs were highly faithful to their homes, usually staying close to the one to three hiding spots they preferred. But during the time the scientists were monitoring them—up to three months—15 of the crabs went on mysterious, long-distance journeys to the coast.

The authors report in PLOS ONE that these journeys were up to 4.2 kilometers long, a distance that might not seem impressive, except that the top speed observed in the study was 150 meters per hour. If you set a shuffling robber crab at one end of a soccer field at the beginning of a game, you just might be able to retrieve it from the opposite end at halftime.

All the journeying crabs traveled along a similar route, sharing a "migratory corridor" toward the ocean. Why do they go on these arduous errands, visiting the coast for 1 to 10 days before returning home? Krieger says he and his coauthors are "convinced that it is most likely a combination of factors."

One possible factor is reproduction; athough they mate inland, male crabs may try to boost their success by pursuing females out to shore. Another is nutrition. Krieger says the crabs may need to drink saltwater to get the calcium and sodium that keep their skin sturdy. They also get the nutrients they need by eating other crabs, such as the red crabs that migrate en masse across Christmas Island every year. Traveling robber crabs may take advantage of this mobile red-crab buffet. (Here's a worthwhile video of red crabs dodging traffic and clinging to cliff faces during their own journeys.)

The fact that male robber crabs traveled at all was news to the scientists. But they also wanted to know how well robber crabs can navigate, and that's where the crabnapping came in. A dozen crabs were bagged, moved a kilometer or so, and re-released to see how they'd manage.

Crabs that were freed somewhere within the migratory corridor, that popular robber crab highway, found their way home with no problem. But those released someplace unfamiliar were lost. The GPS data showed that these crabs used their release points as a new home base from which they took exploratory trips outward, trying to get their bearings. Yet they never found their old homes.

Though robber crabs might navigate using cues such as the position of the sun or moon, the scent of the ocean, or the earth's magnetic field, they seem to especially rely on memorizing a path in one direction and retracing it on the way back. The GPS data showed crabs following identical routes on their way to and from the ocean.

The researchers also crabnapped one of their victims twice, and saw that he followed precisely the same path homeward (along the migratory corridor) both times. This suggests that robber crabs remember the landmarks they find along their routes. Of course, when you're moving at a crab's pace, there's plenty of time to observe the scenery.


Krieger, J., Grandy, R., Drew, M., Erland, S., Stensmyr, M., Harzsch, S., & Hansson, B. (2012). Giant Robber Crabs Monitored from Space: GPS-Based Telemetric Studies on Christmas Island (Indian Ocean) PLoS ONE, 7 (11) DOI: 10.1371/journal.pone.0049809

Image: John Tann (Flickr)

The Hazards of Being an Athletic Ape

This post first appeared at the Scientific American Guest Blog and is republished with permission.

With a single bad step as he ran untouched across a field this September, one of the best cornerbacks in the National Football League removed himself from the game for a whole season. New York Jets fans who saw Darrelle Revis’s left knee buckle under him that day may have pled with their televisions: not the ACL. But it was too late for Revis and his anterior cruciate ligament, which will undergo surgery this week.

Football fans are all too familiar with the ways in which a knee or ankle can fail a person. But athletes, like other humans, are simply doing the best that an ape running around on two legs can.

Before we lived and walked on the ground, our ancestors inhabited the tree branches. They didn’t look quite like chimpanzees or any other modern animal, but they were large apes built for climbing. They had big, grasping toes and extremely flexible feet and ankles. “These things were just brilliantly adapted for living in the trees,” says Boston University anthropologist Jeremy DeSilva. He studies the evolution of ape and human locomotion by looking at both ancient fossils and modern-day animals in motion.

When our ancestors descended from the trees and began walking upright, they faced some major mechanical challenges. “Being on two limbs is just a real problem,” DeSilva says. “If you were taking shop class and your assignment was to build a chair, and you built a chair with two legs, you’d fail the class because it would fall over all the time.” Simply balancing an animal upright is a feat of evolutionary engineering—and that’s before the animal starts moving around.

To walk on two limbs, our ancestors had to make several modifications to the feet they’d inherited from tree-climbing apes. Flexible, grasping appendages with 26 individual bones had to become stable surfaces that we could push off of with each step. “We’ve stiffened things up by patching these bones together with a bunch of ligaments that make up the arch,” DeSilva says. And muscles that were once used for grasping branches now support the foot’s arch. “But boy,” he says, “these are just a bunch of band-aids.”

Though these new two-legged bodies worked well enough to keep our lineage alive, bipedalism may not be the best idea evolution has ever had. “If you look across the animal world,” DeSilva says, “good ways of moving evolved multiple times.” Flight, for example, has evolved many times. So has a streamlined body in swimming animals. But striding on two legs evolved just once in mammals.

The only other animals that walk like we do are birds. And with a couple hundred million years to work on the problem, rather than the mere 5 million or so that we’ve had, birds have come up with what DeSilva thinks is a tidy solution: they’ve fused several bones together to create rigid, immobile feet.

In humans, DeSilva says, “I find the foot to be incredibly problematic.” He thinks a lifetime of walking and running on feet held together by evolutionary band-aids is bound to lead to the kinds of problems people frequently experience: plantar fasciitis, collapsed arches, shin splints, Achilles pain.

What’s more, DeSilva says, “We have evidence that these things are not just modern problems.” In the ancient hominins whose fossils he studies, there are many who suffered from the same injuries that plague us. There are broken ankles in individuals 1.9 and 3.4 million years old (both healed). There’s osteoarthritis in a creature that may have been Homo habilis. An Australopithecus has what looks like a compression fracture in its heel. Another individual sustained, and healed from, a severe high ankle sprain 1.8 million years ago.

Modern-day humans know a thing or two about twisted ankles. The most commonly sprained ligament in the whole human body is a tiny one in the ankle called the anterior talofibular ligament. What’s notable about this ligament, DeSilva says, is that almost none of our living ape relatives has it.

DeSilva’s opinion is that humans evolved this ligament to keep the ankle stable. An upright human is like a balanced stack of blocks, he says. Our ankle bones have flattened surfaces that sit on top of each other, unlike the curved and snugly fitted ankle bones of a chimp. When a human steps on an unexpected rock, this extra ligament in the ankle might be necessary to keep the whole stack of blocks from slipping off its foundation. We don’t dislocate a foot entirely when we trip on a curb—but we might be benched for a couple of months.

Like our ankles, our knees have wide, flattened surfaces that spread out the weight we’re carrying on two limbs instead of four. And they’re large, compared to our body size. “The whole bed-of-nails idea is at work here,” DeSilva says. “Human joints tend to be very puffy.” Structurally, though, our knees are similar to those of our climbing relatives; they have all the same components that a modern chimp’s knee does.

But chimps don’t ever land funny after a layup shot, or change direction too sharply while cutting upfield. That kind of sudden sideways motion is the knee’s downfall, and can rip or snap the ligaments that stabilize the joint.

The infamous ACL sits inside the front of the knee joint, holding the thigh bone in place on top of the shin bone. Its counterpart at the back of the knee is the posterior cruciate ligament. The MCL and LCL, or medial and lateral collateral ligaments, cradle the knee joint on either side and are especially vulnerable to sideways jarring. Too much twisting in the knee can tear the menisci, pads of cartilage tucked inside the knee socket.

Our knees have no problem with the normal folding and straightening of our legs. “When you go too far out of range in the other directions, that’s when you get in trouble,” says Irene Davis.

Davis is a physical therapist and biomechanics researcher at the Spaulding National Running Center at Harvard University Medical School. Despite how often we suffer injuries, Davis says, “I think we’re designed really well for both walking and running.”

Davis cites the theory, promoted by Harvard anthropologist Daniel Lieberman and others, that early humans evolved as so-called persistence hunters. Before they developed effective spears, the theory goes, our ancestors obtained meat by separating an animal from its herd and simply chasing it on foot until it couldn’t run any farther. Researchers point to various skeletal features and cooling mechanisms—and the fact that some people seem to enjoy it so much—as evidence that our species is built for long-distance running.

Of course, early humans would have done it without Reeboks on. In the clinic, Davis advocates what she calls a more natural style of running. She teaches people to land gently on the front of their foot with each step, as barefoot runners do, rather than hard on their heels as people with cushioned running shoes tend to.

Davis believes that wearing structured, arch-supporting shoes makes feet weak and lazy, and that this weakness leads to common foot injuries such as plantar fasciitis. Yet feet are largely ignored until they give us trouble. “You don’t see people at the gym strengthening their feet,” she says, but you should. “Strong feet are healthy feet.”

Despite what DeSilva sees as evolutionary patchwork, Davis thinks the human foot is “just a fantastic structure.” Each time the foot hits the ground, it must be both flexible enough to absorb shock and adjust to uneven terrain and rigid enough to push off of again. Davis thinks the problems come when we don’t use our feet and legs as evolution intended.

When treating patients with overuse injuries, Davis teaches them to run with better mechanics so they avoid getting the same injury in the future. Runners receive feedback on their motion from tools such as accelerometers or mirrors, then practice carrying their bodies in better alignment.

Davis says people can also be taught to prevent future acute injuries such as ACL tears. Most ACL injuries are non-contact; as Darrelle Revis knows, one awkward step is all it takes. So there are programs that teach athletes to land their jumps more gently, or aim to strengthen stabilizing muscles around the knee to protect its ligaments. Though some people will still choose to put themselves in the paths of linebackers, they can at least learn ways to run and jump that put less strain on their vulnerable ligaments to start with.

Having recovered from recent injuries of his own, Jeremy DeSilva will be lacing up his minimalist Nike Free sneakers to run a marathon this weekend. Influenced by the research on barefoot running, he’s left cushioned sneakers behind and is now propelling himself more like his Australopithecus subjects did. “I guess I take my work home with me,” he says.

Davis runs completely barefoot, though in the winter or when she needs more protection for her feet she’ll wear a minimal covering such as water shoes. She also rollerblades.

One sport Davis doesn’t enjoy is football. “I don’t like watching the injuries,” she says. “I see a big pile of people with someone underneath it and it just drives me crazy.”


Image credit: Cpl. Michelle M. Dickson

The Shambulance: Infrared Body Wraps

(The Shambulance is an occasional series in which I try to find out the truth about bogus or overhyped health products. Having recovered from my taste of no-calorie noodles, I'm back this week with Shambulance first officers Steven Swoap and Daniel Lynch.)

Sometimes it's for the best when product claims turn out to be blatant lies. If purveyors of infrared body wraps, for example, were telling the truth, clients would walk out of their spas dripping grease from their skin—and that wouldn't even be their biggest concern, next to the heart attacks.

All body wraps are not created equal. There are slimming volcanic ash wraps, herbal wraps, mud wraps, and even chocolate wraps. Some are only meant to be relaxing skin treatments. Others involve swaddling clients mummy-style in bandages and plastic wrap, then leaving them for an hour or so to stew in their own sweat.

These kinds of body wraps often promise weight loss or overall slimming. In reality, how much weight you lose will depend on how much water your body sweats out in a frantic effort to cool down. Additional svelte-ness might come from the squishing action of the tight bandages. Both effects will be temporary. 

As another benefit, spas that offer body wraps unfailingly promise "detox." This isn't the first time the d-word has come up here. Suffice it to say that unwanted molecules are filtered from our blood and sent out of our bodies by the liver and kidneys—not sucked from us forcefully by mud wraps, juice diets, or ionic foot baths.

But the most amazing promises of all come from the infrared body wrap. Unlike some of the body wrap's other incarnations, this treatment doesn't require you to strip down, be slathered in goo, and get bandaged head to toe. Instead, clients lie on a bed with their clothes on while several infrared-generating silicone pads are strapped around them. Then they're left under a heated blanket for a while.

So far, it sounds like nothing more than a toasty nap. But spas say that you'll leave an infrared wrap session skinnier and healthier, with better circulation, a faster metabolism, clearer skin, and less cellulite. How?

The pads give off long and short infrared waves that penetrate deep into your fat layers, websites claim, increasing your body temperature, metabolism, and blood circulation. The heat "break[s] down fats into a liquid form, allowing secretion of body water, toxins and fat as you perspire," according to one Chicago spa.

All that formerly stored fat, once liquefied by the infrared waves, is obviously eager to escape your body through the nearest exit. But don't worry if the fat gets stuck inside you—you'll burn it anyway. "You can burn 900 to 1,400 calories or more in just one 50 minute session," another Chicago site proclaims.

After studying this calorie chart, I'm thinking I've been wasting my time by walking to work. What I should really do is buy some of these silicone pads, strap them on, and see if I can get someone to roll me there.

This is "completely insane," says Williams College physiologist Steven Swoap. "How are they allowed to write this stuff?"

For one thing, "Fats simply don't come out of sweat glands," he says. Though if they did, you would definitely have to throw away your spa outfit after soaking it with grease from the inside.

Infrared radiation, Swoap explains, isn't a magical cellulite-blasting weapon. In fact, people naturally give off long infrared waves as body heat. "Instead of wrapping yourself with this stuff, maybe a good long hug with your significant other would work too," Swoap says. Or, if you're looking for shorter infrared waves, "You could take your TV zapper and shoot it at yourself all day long."

Daniel Lynch, a Williams College biochemist, says that heating parts of your body could certainly increase your water loss. But your fat isn't budging. "To get rid of the fat, it must be metabolized," he says, "and that is not going to be enhanced by lying on a bed with silicone wraps on your legs."

Furthermore, Lynch speculates, if your fat deposits really did get broken down and sent back into your blood—and you were, say, lying on a table instead of using those fat molecules for fuel—"You could actually have dangerous levels of fatty acids circulating in your blood. That's good for a heart attack!"

If you're looking for an exercise-free way to burn fat, Swoap suggests hanging out in a cold room rather than under a warm blanket. Being in the cold will raise your metabolism as your body tries to replace the heat you're losing. If you're still hankering after the spa experience, you could always wait until winter, wrap up in a scarf, and have someone log-roll you down the sidewalk.

Images: Top, Leah Chavie Skincare Boutique; middle, Formostar Infrared Body Wrap System; calorie chart, Formostar Infrared Body Wrap System.

How to Unstick a Gecko

During a downpour in the rainforests of Southeast Asia, one sound you will not hear is the patter of geckos hitting the ground. Their sticky feet keep them adhered in habitats all over the world, from jungles to deserts to glass-windowed cities. Yet scientists have found that there is one way to loosen the lizards. Soaking geckos’ feet in water, or submerging the surface they walk on, defeats their sticky superpower—and gives new clues to researchers trying to replicate it for human use.

Gecko feet have inspired much investigation and imitation by human scientists, who have found that the animals take advantage of attractions between molecules called van der Waal’s forces. These attractions are ordinarily very weak. But the soles of geckos’ feet are covered with tiny, branched hairs that end in flattened pads. This increases the surface area of the feet so much that the weak van der Waal’s forces add up to an adhesive power strong enough to hold a gecko upside-down on a ceiling.

The hairs also strongly repel water, a feature called superhydrophobicity—"an exciting word!" says Alyssa Stark, who's a graduate student in the integrated bioscience department at the University of Akron. “It could be a byproduct of having so many hairs, and those hairs having a certain surface chemistry, and that’s it,” Stark says. In other words, water repellence might be a gratuitous feature, the extra cup-holder of the lizard world. “But I was kind of curious to see if there was anything else to that story.”

Stark led a study to find out whether superhydrophobic toes help geckos hold on in the rain. To simulate various weather conditions, researchers had their seven subjects walk on glass that was dry, misted with water, or submerged in a shallow puddle. In some trials, the geckos' feet were left dry; but in others they got a leisurely 90-minute soaking in a tub. (It's tough to get those foot pads wet, Stark says. Normally, water beads and rolls off of them.) 

After placing the geckos onto the glass surface, the researchers coaxed them into taking one step at a time with a harness attached to their pelvis (Stark describes the geckos as "not necessarily cooperative" during this procedure). The harness was connected to a device that gradually tugged backward on the geckos until they lost their footing, measuring how much force it took to unstick them.

The results, published today in the Journal of Experimental Biology, showed that water impairs geckos. When walking on a submerged surface, or with soaked toe pads, the geckos struggled to stay in place. It took much less force than usual to pull them free from the glass. 

When the geckos walked on a surface misted with water droplets—the condition that most resembled something the animals might find in their natural habitats—things got interesting. The geckos slid more than usual, but weren't totally defeated. “Even though they have lost a significant portion of their stickiness, they can still hang onto a misted glass surface,” Stark says.

That water-repelling power on their foot pads, then, seems to come in handy. Getting soaked would unstick their feet, but geckos are able to prevent this in damp conditions by quickly shedding water drops from their soles. Stark now wants to find out how wild geckos behave in wet weather. Do they walk like normal and let their superhydrophobic feet do all the work? Or, to avoid slipping, do they stay away from wet areas altogether?

Stark is not only a biologist; she's also a polymer scientist. So when she asks how gecko feet work and how the animals compensate for their shortcomings, it's because she's interested in ripping off their technology for human use. We're already well on our way.

"Materials scientists have created many 'gecko-tape' synthetics that are reusable and sometimes work even better than the gecko," Stark says—in dry conditions, that is. Scientists at the University of Berkeley have built a gecko-inspired adhesive that lets a car drive up a precipitous incline (though only on a perfectly smooth "road") and, like gecko toe pads, self-cleans by casting off any particles that stick to it. In Germany, researchers at the University of Kiel created a gecko tape that can hold an adult human with just an 8-by-8-inch square.

Other synthetic coatings and surfaces have been designed to repel water. Combining the two technologies to create a stick-anywhere tape that can handle a little water "would be ideal," Stark says. If we can figure out the trick, we can make adhesives that are more powerful and more versatile, she says—"in essence, more like the gecko."

Alyssa Y. Stark, Timothy W. Sullivan, & Peter H. Niewiarowski (2012). The effect of surface water and wetting on gecko adhesion Journal of Experimental Biology DOI: 10.1242/jeb.070912

Image: A gecko with wet feet slipping, from video by Alyssa Y. Stark

Inner Ears Reveal Speed of Early Primates

It's 20 million years ago in the forests of Argentina, and Homunculus patagonicus is on the move. The monkey travels quickly, swinging between tree branches as it goes. Scientists have a good idea of how Homunculus got around thanks to a new fossil analysis of its ear canals and those of 15 other ancient primates. These previously hidden passages reveal some surprises about the locomotion of extinct primates—including hints that our own ancestors spent their lives moving at a higher velocity than today's apes.

Wherever skeletons of ancient primates exist, anthropologists have minutely analyzed arm, leg, and foot bones to learn about the animals' locomotion. Some of these primates seem to have bodies built for leaping. Others look like they moved more deliberately. But in species such as H. patagonicus, there's hardly anything to go on aside from skulls.

That's where the inner ear canals come in. "The semicircular canals function essentially as angular accelerometers for the head," helping an animal keep its balance while its head jerks around, says Timothy Ryan, an anthropologist at Pennsylvania State University, University Park. In the new study, he and colleagues used computed tomography scans to peer inside the skulls of 16 extinct primates, spanning 35 million years of evolution, and reconstruct the architecture of their inner ears.

Also called the bony labyrinth, the area in question is a set of three twisting cavities, one oriented along each axis of the body. The sloshing of fluid inside the canals provides information for an animal's system of balance. An earlier study of living and recently extinct mammals showed that more agile or acrobatic animals have bigger semicircular canals relative to their body size. A sedentary sloth, for example, has small and insensitive canals. A gibbon needs larger, more sensitive canals to keep its head and gaze stabilized while it trapezes through the tree branches.

When the researchers scanned the extinct animals' bony labyrinths, some unexpected results emerged. One came from the species Apidium phiomense. Found fossilized in Egypt, this is one of the earliest anthropoids (a group that includes monkeys, apes, and humans). Apidium's skeleton suggests a creature adapted for leaping. Inside its skull, though, were the smaller canals of a less agile animal. "That was definitely a surprise," Ryan says. Given the previous research in living species, mismatches between an animal's locomotive style and its canal size should be uncommon. Apidium may have been slower than we thought, Ryan notes, or its inner ear may have lagged behind while its skeleton evolved rapidly for agility.

Another twist came from a species of Proconsul, "the best-known early ape," Ryan says. From its extensively studied skeletal fossils, "It was considered to be kind of a slow, cautious quadruped in the trees," Ryan says. The ear canals of Proconsul heseloni were larger than expected, suggesting a more agile animal. "Now we believe that it's probably more like a macaque," Ryan says, a primate that moves at a modest pace but is able to leap and clamber at times.

The findings, published last month in the Proceedings of the Royal Society B, "suggest that the basal ape, that first common ancestor of apes and humans, was faster than we would have thought," Ryan says. The slower locomotion of today's gorillas and humans, rather than being inherent to apes, may have evolved later on.

"This is really valuable because it gives us another source of data to say what an extinct organism might have been doing," says Laura MacLatchy, an anthropologist at the University of Michigan, Ann Arbor, who was not involved in the research. She points out, however, that P. heseloni is on the smaller side of the four or five species of Proconsul. The larger species may have moved more slowly. Rather than representing how the original apes moved, P. heseloni might simply be a more agile member of a diverse genus.

Researchers will need to delve deeper into the fossil evidence to resolve the apparent mismatches between the inner ear and skeleton, as in Apidium. Ryan says that further studies in living primates, too, will help clarify the relationship between an animal's semicircular canals and its style of movement. Eventually, we may be able to put more of our long-fossilized relatives back into motion.

This piece was first published on June 22 at ScienceNOW.


Image: Timothy Ryan/Pennsylvania State University

Ryan TM, Silcox MT, Walker A, Mao X, Begun DR, Benefit BR, Gingerich PD, Köhler M, Kordos L, McCrossin ML, Moyà-Solà S, Sanders WJ, Seiffert ER, Simons E, Zalmout IS, & Spoor F (2012). Evolution of locomotion in Anthropoidea: the semicircular canal evidence. Proceedings. Biological sciences / The Royal Society PMID: 22696520

Weightless Flies Have Wanderlust

To astronauts, science fiction writers, and entrepreneurs selling tickets on private space flights, the question of how weightlessness affects an organism is crucial. Our cells and organs are fine-tuned for life within the comfortable harness of Earth's gravity, so what happens to them when we're cut loose? There's at least one way to study this question without the prohibitive price tag of sending something all the way to space. A group of magnetically levitated fruit flies, though they couldn't report on their experience, seemed to find it just as good as the real thing.

University of Nottingham researcher Richard Hill and his colleagues used a powerful magnetic field to create a small, zero-gravity "arena" for fruit flies. Though magnetic fields attract magnetic substances such as iron, they also weakly repel certain other materials that are called "diamagnetic." These include water and organic matter--in other words, most of what's in a fruit fly. (Or in you. But there isn't a magnet big enough to try this trick on a person.)

By carefully aligning their disc-shaped fly arenas inside a superconducting solenoid magnet, the researchers were able to create environments of roughly 1g (equal to Earth's gravity), 2g (twice Earth's gravity), and 0g (whee!). They also left one fly dish outside the magnet, so they could compare the 1g environments and make sure the magnetic field didn't just make all the flies crazy.

Though the researchers provide many mathematical descriptions of their result, you can see it easily and immediately in this video. The 0g flies are on the top left.

Fruit flies' normal behavior is to roam, but the 0g flies are tearing around their dish.

Unlike human astronauts, who don't have much choice but to float, fruit flies have grippy little feet and the power of flight. So the weightless flies spent most of their time walking on the floor, walls, and ceiling as usual. (You might spot a few of them floating dazedly in the center of the dish, though.) What was unusual was the speed and amount that they traveled.

This might be simply because it's easier for flies walk without gravity. If it takes less energy than usual to walk, a fruit fly that's putting the normal amount of effort into moving around will find itself at a near-sprint. The 2g flies supported this theory by walking more sluggishly than usual.

Another possibility is that the flies' altered perception of gravity affected their behavior. Like human astronauts who go ricocheting off the walls for fun, the fruit flies might have noticed something was different and reacted to that feeling.

The finding that weightless flies speed-walk isn't new: Experiments done on the International Space Station and on the space shuttle Columbia found the same result. But replicating the finding here on Earth shows that it wasn't a fluke caused by some other factor, such as the trauma of takeoff. The flies' altered behavior was directly due to their low-gravity environment, making it relevant to humans and any other organisms we might carry into space.

Hill's study also shows that zero-gravity experiments, at least on very small organisms, don't have to be done in space. Studies done inexpensively here on Earth can provide real insights into life in outer space, and help create safer technologies for the lucky humans who get to go.

Hill, R., Larkin, O., Dijkstra, C., Manzano, A., de Juan, E., Davey, M., Anthony, P., Eaves, L., Medina, F., Marco, R., & Herranz, R. (2012). Effect of magnetically simulated zero-gravity and enhanced gravity on the walk of the common fruitfly Journal of The Royal Society Interface DOI: 10.1098/rsif.2011.0715 


Movie: Hill et al., data supplement; Photo: NASA

It's Harder to Dodge Sharks When Pregnant

Although it would be nice to hatch our babies from eggs Anne Geddes-style, or deliver them while still tiny and carry them around in a pouch, humans and other placental mammals are stuck lugging their developing fetuses inside their bodies. Luckily, most humans aren't in danger of predation. But for animals that sometimes have to run (or swim) for their lives, pregnancy can be dangerous.

In a punnily titled new study ("Pregnancy is a drag"), UC Santa Cruz researcher Shawn Noren investigates how pregnant dolphins are affected by carrying a wide load. Noren studied two captive bottlenose dolphins, each about 10 days away from giving birth, living in a lagoon in Hawaii.

Though the study only included these two dolphins, Noren collected many data points by having a scuba diver sit underwater and videotape the dolphins swimming back and forth. The dolphins were also observed and recorded periodically during the two years after they gave birth. By digitizing these videos, the researchers could quantify the dolphins' size, mass, surface area, swimming speed, and swimming mechanics.

As expected, very pregnant dolphins had a very much larger surface area. This created greater drag as the dolphins glided through the water. The dolphins also changed their swimming "gait," like a human who finds herself a little waddle-y in the final trimester. Dolphins get all their forward thrust from the up-and-down beats of their tails. The pregnant dolphins beat their tails a little more shallowly than usual, maybe because their muscles were stretched out and weakened by the fetus (or because their midsections were less flexible). Just like a human taking smaller steps, a dolphin making smaller tail-beats covers less distance. So the pregnant dolphins had to beat their tails faster to maintain a given speed.

Besides experiencing greater drag and a shortened "stride," pregnant dolphins have altered blood flow and lower lung capacity. They also store more lipid (fat) than usual in their blubber, making them extra buoyant. All these factors combine to slow a dolphin way, way down. The two pregnant dolphins in the study swam more than 60% slower, on average, before their calves were born. After recovering from pregnancy, the dolphins' average swimming speed was around 9 mph. But before giving birth, their speed was closer to 3.5 mph--similar to the pace of a walking human.

The crucial factor in avoiding predators such as sharks, though, is maximum speed. After pregnancy, the dolphins reached maximum swimming speeds of more than 14 mph. While heavily pregnant, they barely reached 8 mph. Of course, the researchers didn't introduce any sharks or killer whales into the lagoon to see how fast the dolphins could swim under real duress. But the researchers note that at the fastest swimming speeds they observed, pregnant dolphins would not have been able to out-swim most predators.

It's unknown whether pregnant dolphins are more vulnerable to predators in the wild. But among ungulates--hoofed mammals such as buffalo or wildebeest, which happen to be close relatives of whales and dolphins--pregnancy is a known risk factor for being eaten by lions. In dolphins, the greater effort needed to swim while pregnant probably means they need to take in more calories. But it also must make hunting for food more difficult. A pregnant dolphin will have a harder time chasing after quick prey or, because of her increased buoyancy, diving to hunt.

In humans, studies of how pregnancy affects walking have been inconclusive. This might be because there's a great deal of variation in how individuals' bodies adjust to pregnancy. These two dolphins, too, may not be representative of their whole species. But they demonstrate the amazing adaptability of a female mammal's body, whether she's diving for squid or just shuffling through the suburbs.

Image: Shawn Noren/JEB

Noren, S., Redfern, J., & Edwards, E. (2011). Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus) Journal of Experimental Biology, 214 (24), 4151-4159 DOI: 10.1242/jeb.059121