Field of Science


Interview with an Inkfish

It's Halloween, and I may not be wearing a scary costume, but I have snuck up on the Chimeras blog.

As part of her Author Interviews series, E. E. Giorgi asked me what it's like to write about science for kids (and adults). Click here to read our conversation about junior paleontologists, PCR, and unconvincing threats.

Why Don't Woodpeckers Get Concussions?

To help protect our big, fragile brains from trauma during sports, why not turn to another animal that voluntarily smashes its skull into solid objects? The woodpecker hammers its beak into tree trunks twelve thousand times a day at at fifteen miles an hour. In so doing, it drills out nests, finds tasty bugs, and does not (as far as one can tell) give itself brain damage. What's its secret?

Lizhen Wang at Beihang University in Beijing led a study to find out what makes the woodpecker so resilient. The team used Dendrocopus major, the great spotted woodpecker, which is common in China. For comparison, they also studied the Eurasian hoopoe,* a relative that pecks soft soil instead of wood.

With the birds caged, the researchers used high-speed cameras to record their pecking motions and sensors to measure the force with which the birds struck the metal cage or a piece of foam. They also took detailed scans of the birds' skulls, examining them at a microscopic level. After mechanically testing pieces of woodpecker skull and beak, the researchers used those results to create a computer model of a woodpecker head. Then they virtually smashed the model head into a tree trunk, tweaking different parameters and observing the effects.

"Simple reasoning would indicate that if woodpeckers got headaches, they would stop pecking," Wang writes. The researchers' interest was not just in preventing headaches, of course, but the disability and death that can accompany hard head whacks in humans. Sports organizations have started to recognize the danger of repeated concussions, especially concussions that follow close on the heels of earlier ones. In 2009, the NFL changed their rules about how soon concussed players can return to a game. But even without serious concussions, repeated blows to the head might lead to chronic traumatic encephalopathy (CTE), a degenerative disease of the brain that can cause dementia and personality changes. Athletes themselves are becoming wary of CTE, too. Former NFL player Dave Duerson illustrated that brutally earlier this year, when he committed suicide by shooting himself in the chest so that doctors could examine his brain for CTE. (They found it.)

Some of what Wang found in woodpeckers is of no immediate use to athletes. For example, some of the woodpecker's sturdiness comes from the hyoid bone, a nifty sling-shaped structure that extends from the top of the head through the skull to the nasal cavity. This bone (letter b below) only exists in woodpeckers. Additionally, the woodpecker's beak, with its uneven upper and lower parts, is calibrated to absorb much of the blow.

Humans can't very well insert stabilizing bones behind our faces or grow beaks that absorb an impact like the front of a car. But findings about the woodpecker's skull bones might be more useful. Compared to the hoopoe, the brain of the woodpecker is packed tightly in dense bone. The hoopoe's skull contains more spongy bone, an airy-looking material made of branches surrounding pockets of space. The woodpecker's spongy bone has less space inside it and looks compressed, like sheets of bone stacked on one another. The woodpecker skull is preferentially padded with this spongy bone at the forehead and the back of the skull.

If we can incorporate some of the woodpecker's evolved technology into future helmets, we may be able to better protect ourselves from the recreational activities that threaten our brains, from field sports to bicycle riding. We may be the more cerebral species, but the better-protected birdbrain could help keep us alive.

*Linguistic point of interest: "hoopoe" is from the Latin upapa, an imitation of the bird's call.

Images: Wang et al.

Wang, L., Cheung, J., Pu, F., Li, D., Zhang, M., & Fan, Y. (2011). Why Do Woodpeckers Resist Head Impact Injury: A Biomechanical Investigation PLoS ONE, 6 (10) DOI: 10.1371/journal.pone.0026490

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Clocks, Cancer, and the Best Time to Tan

If you can't bear to face your inbox before your first cup of coffee, you'll sympathize with cells in your body that are better equipped to face some challenges at certain times of day. Carcinogens, such as ultraviolet radiation, may be one such challenge. Can we lower our cancer risk by limiting our carcinogen exposure to certain hours of the day?

Circadian rhythms are day-long cycles that ebb and flow like tides within our bodies. We use the sun to keep our internal clocks calibrated. But even if left in a dark room for days on end, our bodies maintain their rhythms. Our internal temperatures, levels of circulating hormones, and activity of various genes within our cells all rise and fall throughout the day.

One of the genes that follows a daily cycle is responsible for making a DNA-repair protein called XPA. When your DNA is damaged, a molecular task force within the cell identifies the bad spot, snips it out, and fills in the gap with fresh nucleotides. XPA is a crucial member of this task force. Researchers in North Carolina wanted to know how the cycling of XPA affects skin cancer. When XPA is off-duty--when its daily cycle reaches its lowest point--are skin cells more vulnerable to cancer-causing sun damage?

To find out, the researchers used hairless mice that are bred to develop humanlike skin cancer. Mice have an internal clock that's nearly identical to that of humans, and repair their DNA in the same way. The researchers exposed one group of mice to UV radiation at 4 AM, the lowest point of their XPA cycle. Another group of mice was exposed at 4 PM, the high point, instead.

For the 12 hours following UV exposure, the researchers monitored the rate of DNA repair in mouse skin cells. They saw that in the afternoon group, repair happened quickly, thanks to the high amounts of XPA at work. But in the morning-exposure group, DNA repair was delayed significantly.

Does this delay in fixing DNA errors add up to cancer? The researchers again divided the mice into groups. One group was exposed to UV radiation at 4 AM, three days a week, for 25 weeks. The second group was again exposed to UV at 4 PM, and a third group was left alone.

Both groups of mice exposed to UV developed skin tumors. But the group that got its UV radiation in the early morning grew tumors sooner. Those mice also had twice as many tumors as the afternoon UV group, and their tumors were nearly twice as wide. (All this evidence was easily, and disgustingly, visible due to their hairlessness.)

In humans, damage and repair likely follow the same rhythm. But there's one major difference: Since mice are nocturnal, their clock is opposite to ours. Hormones that are needed during waking hours, for instance, would peak during the night in mice and during the day in humans. In an earlier study, the researchers found that XPA follows a circadian rhythm in humans just as it does in mice--but for us, production is highest in the early morning.

Our levels of XPA peak around 7 AM. Based on this study, our ability to protect our skin from cancer-causing sun damage probably peaks at the same time. Adding to the danger is the fact that in both humans and mice, DNA replication follows a cycle opposite to XPA production. This means that when XPA is lowest, more DNA is being stitched together--making the risk of errors even higher.

The authors suggest that if we must expose ourselves to UV radiation, we do so in the morning. We should avoid the sun in afternoon and evening hours, when XPA is lowest and our skin cells are most vulnerable to carcinogenic damage. Of course, unless you live in the Arctic circle, you're not likely to get a lot of dangerous sun exposure at 7 PM. But for people who use tanning beds, sessions late in the day may be more harmful than those in the morning.

There may be other carcinogens whose danger varies throughout the day, depending on how hormones and other molecules are cycling through our affected organs. Is there an ideal time of day to smoke a cigarette? Eat a hot dog? Have an x-ray? If we can't remove risks from our lives, maybe we can at least reschedule them.

Gaddameedhi, S., Selby, C., Kaufmann, W., Smart, R., & Sancar, A. (2011). Control of skin cancer by the circadian rhythm Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1115249108

Are Women Really Less Funny than Men?

Did you hear the one about how men are the funnier sex? If not, you're alone. In a recent study of California undergrads, 89% of women and 94% of men not only were familiar with the stereotype, but agreed with it. To investigate whether this supposed humor discrepancy might be a fact, the study's authors set up a tournament of New Yorker cartoon captions.

In a format you'll recognize if you've ever been sucked into the New Yorker cartoon caption contest, 32 subjects were given a series of uncaptioned drawings (like the one above) and told to supply the funniest possible punch line. The subjects, half male, sweated through 20 of these captions before finally being relieved with a questionnaire: Do you think men or women are funnier? How funny do you think your captions are?

Then 81 more subjects acted as raters for the captions. For each of the 20 cartoons, captions were paired off tournament-style. In the first round, subjects saw each cartoon with 16 pairs of captions and indicated, for each pair, which one was funnier. In round two, the surviving captions were shuffled and paired off again, and so on until each rater had picked one winning caption per cartoon. The subjects didn't know the gender of the caption authors.

The result was a very slight, but statistically significant, advantage for male caption writers. The advantage was a bit larger when only looking at male raters: Men seemed to prefer captions written by other men.

Analyzing the captions afterward for their content, the researchers found that males were somewhat more likely to use sex and profanity in their gags. But these jokes weren't responsible for the advantage male caption writers received from male raters. Instead, it seems guys just got each other.

I don't have to point out that writing a New Yorker cartoon caption is a very specific kind of humor. I will, though, raise one question about the tournament scoring system. The authors awarded captions one point for each round of the tournament that they survived, from 0 to 5. That's one point for each matchup won. But a caption that survives, say, the third round of the tournament hasn't beaten just three other captions--it's beaten seven. A caption that wins its whole tournament has beaten 31 others, but only gets five times as many points as a caption that beats one other. Essentially, the scoring system undervalues the funniest captions. If these captions were all written by men anyway, it wouldn't change the results. But not knowing who wrote what captions, I'd be interested to see the data interpreted with a different scoring system.*

Why should men be funnier than women, anyway? Some scientists have suggested it's all evolutionary: joke-telling is a flashy feature, like large antlers or elaborate ribbit-ing, that advertises a male's worth to females. Men are more likely to tell jokes, they say, and women are more likely to laugh at them. Writer Christopher Hitchens endorsed the evolutionary view in an article titled "Why Women Aren't Funny":
If you can stimulate her to laughter—I am talking about that real, out-loud, head-back, mouth-open-to-expose-the-full-horseshoe-of-lovely-teeth, involuntary, full, and deep-throated mirth[...]—well, then, you have at least caused her to loosen up and to change her expression. I shall not elaborate further.
(And I did not read any further, because that passage made me open my lovely mouth and vomit.) 

Laura Mickes, author of this paper, points out that sexual selection wouldn't explain why men are mostly funnier to other men. And regardless of what evolutionary pressures may have existed in our past, today it's impossible to untangle their effects from those of culture. Anyone who grows up with a TV knows that women sigh a lot and cook dinner while their Ray Romano-esque husbands goof around and think of snappy one-liners. Boys are supposed to get muddy and tell jokes; girls are supposed to be polite and not ask for too much attention. Rather than being unfunny, are women just unpracticed? The female caption writers in the study had very low expectations of their own humor, rating their own captions significantly worse than men did.

The second part of the experiment addressed the question of culture, asking whether people are likely to falsely remember funny jokes as being told by men. The researchers used the 50 funniest and 50 least funny captions from the first experiment. A new group of subjects were shown cartoons and captions labeled with the author's gender, and asked to remember the sources of the captions. Later, subjects were shown the same captioned cartoons and asked to recall each caption writer's gender. Though the captions in the test were balanced for gender, subjects were more likely to misattribute funny captions to men and unfunny captions to women.

Whether or not men really have an edge in humor, it's clear that pretty much everyone believes they do. That's not especially funny. Being a woman, though, I'll try to laugh it off.

This post was chosen as an Editor's Selection for ResearchBlogging.orgLaura Mickes, Drew E. Walker, Julian L. Parris, Robert Mankoff, & Nicholas J. S. Christenfeld (2011). Who’s funny: Gender stereotypes, humor production, and memory bias Psychonomic Bulletin & Review

*Thanks to Doug, my husband and resident bracket expert, for pointing out the scoring problem.

Image (c) Mick Stevens/The New Yorker Collection/

Like a Hot Dryer, Climate Change Shrinks Species

Species of the near future, like a new sweater you accidentally put through a tumble-dry cycle, may be smaller and less useful than you remember them. Organisms from polar bears to plants to farmed fish are already losing stature. As the world gets hotter and rainfall gets more sporadic, countless other species are expected to shrink, too--provided they don't disappear altogether.

The authors of a new paper in Nature Climate Change compiled data from dozens of studies on species size and climate change. They had reason to expect that many species would be shrinking in response to global warming. Animals and plants have already been observed breeding earlier, flowering sooner, and gradually shifting their ranges toward the poles (and cooler temperatures). Additionally, the fossil record tells us that invertebrates and small mammals shrank during ancient periods of warming. On those occasions, though, the thermostat was turned up gradually--nothing like today.

The review found that 38 species of animals and plants have recently shrunk. The shrinkage wasn't universal, though; an equal number of species have been observed not shrinking in recent years, or provided equivocal results. And a handful of species have actually increased in size (more on them in a moment).

The species seen shrinking include representatives from the mammals, birds, reptiles, amphibians, fish, and trees. There's reason to believe that these species are trendsetters, not outliers, and that more of the so-far unchanging species will soon follow in their footsteps (or hoofsteps or wakes). If climate change is to blame for miniaturizing animals and plants, then this effect should become more obvious as the earth gets warmer.

And according to experimental evidence--not just the circumstantial evidence of species happening to shrink during the past few decades--climate change is to blame. Controlled experiments have shown that increased temperatures cause plants, fish, marine invertebrates, beetles and salamanders to grow smaller. Other studies have found that reduced precipitation produces smaller mammals, frogs and toads, and tropical trees. In the ocean, acidification caused by increased carbon dioxide in the water is known to impede the growth of corals, scallops, and other animals that build calcified bodies for themselves. Acidification also slows the growth of phytoplankton, the microscopic plants that hold up the whole ocean ecosystem. (And, don't forget, ocean acidification creates ambidextrous fish.)

There are a few ways that warmer temperatures could shrink species. In "cold-blooded" or ectothermic animals, including fish, reptiles and amphibians, a higher temperature speeds up the metabolism. Unless animals can readily find more calories to consume, this means they'll burn through their fuel faster and have fewer resources left over for growing their bodies.

For animals that maintain their metabolic rate on their own, namely birds and mammals, shrinkage might have more to do with a lack of resources. If heat or drought kill (or shrink) the species that animals feed on, they'll have to compete more to stay alive. Undernourished animals, including humans, don't grow as big as well-nourished ones.

Some regions, rather than experiencing drought, are expected to become wetter with climate change. But even these areas will have more variation in rainfall than they're accustomed to--that is, there could be periods of drought in between the rainy periods. Less consistent rain will cause plants to shrink or die. Even though increased carbon in the atmosphere might be expected to give a boost to plant life (it's called the greenhouse effect, after all), plants can't take advantage of that extra carbon without sufficient water and nutrients and a comfortable temperature. The few plant species studied so far have shriveled, not grown, in response to climate change.

Over successive generations, evolution might favor smaller individuals within species: Those that need fewer resources might be more likely to survive. The survivors, then, would pass their small-bodied genes to their offspring, and the effects of climate change would be written into animals' genomes for good.

As for those few species that are growing instead of shrinking? They're mostly at high latitudes, where a slight increase in temperature is a welcome relief from the cold. As temperatures rise even more, those species might not be so happy with the change. The species that are most likely to benefit from increased temperatures, or at least not to be too bothered, are predators that can adjust their diet to a wide range of prey. Certain invasive species, which have already demonstrated their handiness at eating anything available to them and adapting rapidly to changing conditions, might also be unscathed.

The authors point out that if every species on the planet shrank at the same rate, we'd all be fine: Within each Polly-Pocket ecosystem, everything would stay in balance. But since species are responding differently to climate change, with some already shrinking and others not, we can expect to see food chains getting bunched up or broken. As those lower on the food chain grow smaller (or, failing to adapt, go extinct altogether), species that eat them will find less food in their meals than they're used to.

This applies to humans, too. Both farmed and wild fish have already been observed shrinking, and heat and drought threaten our crops. Meanwhile, of course, the human population is growing. As climate change leads to food shortages for various groups of people, and undernourished children fail to grow as large as their parents, then even the human species might start shrinking.

Sheridan, J., & Bickford, D. (2011). Shrinking body size as an ecological response to climate change Nature Climate Change DOI: 10.1038/nclimate1259

Who Needs Pheromones When You've Got a Rotten Banana?

"The courtship chamber was placed on top of an identical chamber, with the chambers separated by muslin gauze," reports geneticist Yael Grosjean in a Methods section fit for a paperback romance. Then the "perfumed" portion of the experiment began. An aphrodisiac scent was presented on the other side of the muslin gauze. Scientists watched to see whether the subject, a male fruit fly, would be compelled to start courting his partner. To ensure that the female wouldn't influence the results with her responses, she had been recently frozen to death.

(This may seem unromantic, but keep in mind that in another part of the study, the females were headless. It didn't deter the males.)

A male fruit fly displays a scripted set of actions when courting a female, beginning with a buzzy sort of love song and ending with the deposition of his extraordinarily long sperm. Many animals use pheromones, chemical messages wafting through the air, to attract partners. But, Grosjean says, scientists haven't yet found the hardware in a male fruit fly's brain that would respond to pheromones. So what other chemical signals might the fruit fly be sensing when it decides to court a female?

Grosjean's research team identified neurons in male Drosophila melanogaster that detect scent and extend into a part of the brain involved in sexual behaviors. They found that when these neurons weren't working properly, males failed to court (headless) females. Once they knew the neurons were important for courtship behaviors at the brain end, the researchers investigated what was happening at the "nose" end. They exposed the neurons to the smell of fly bodies, both up close and at a distance (as they would be if pheromones were involved). But the neurons didn't respond.

The researchers proceeded to test another 163 odors on the frigid cells until they found a couple of smells that turned them on: phenylacetic acid and phenylacetaldehyde. These aromatic compounds come not from flies, but from plants. (They also lend their honey-like scent to some of the perfumes manufactured by humans.)

These molecules are common in fruit and vegetable matter, including overripe bananas and prickly-pear cactus, two of Drosophila's preferred foods. To understand why mealtime puts fruit flies in the mood for mating, it helps to know that they lay their eggs in their food. (I guarantee this will occur to you the next time you see buzzing visitors inside the pastry display case at your favorite coffee shop.) To a fruit fly, vegetables and fruits are good places to eat, mate, and start a new generation.

It's a surprising evolutionary solution to the problem of helping tiny flying animals find each other and mate. Pheromones work for some other species, but for fruit flies, the smell of a good egg-laying environment might be enough.

The question of whether humans release or detect pheromones, tantalizing though it is, remains unresolved. Maybe scientists would have more luck if they looked for environmental cues humans respond to, rather than molecules released by other humans. I wouldn't expect prickly-pear cactus to be the next hot perfume, but you never know.

Grosjean, Y., Rytz, R., Farine, J., Abuin, L., Cortot, J., Jefferis, G., & Benton, R. (2011). An olfactory receptor for food-derived odours promotes male courtship in Drosophila Nature, 478 (7368), 236-240 DOI: 10.1038/nature10428

This post was chosen as an Editor's Selection for

How the Need to Pee Helps (and Hurts) Decision Making

The Ig Nobel awards are an annual, tongue-in-cheek version of their namesake, recognizing researchers for ridiculous-sounding papers ("How to Procrastinate and Still Get Things Done") and obscure areas of study (why do certain Australian beetles continuously attempt to mate with discarded beer bottles, even as ants chew off their genitalia?). Sometimes, the awards editorialize on the year's news: Erroneous doomsday predictor Harold Camping won this year's mathematics prize "for teaching the world to be careful when making mathematical assumptions and calculations".

The best Ig Nobel winners, though, start with a silly question and end up with an interesting answer. This year, the prize in medicine went to two different research groups pursuing the same burning question: What happens to our cognitive abilities when we really, really have to pee?

One paper examined subjects' speed in a memory-based test. The adult subjects watched playing cards flipping over on a screen and had to press keys to indicate whether the cards were red or black and whether each card matched the previous one. Oh, and every 15 minutes they had to drink another 250 ml of water.

The researchers repeatedly asked subjects to rate their urge to urinate on a scale ranging from "not at all" to "the most I have ever felt in my life." It took an average of two hours and 20 minutes, and a little over two Nalgenes' worth of water, for subjects to reach the desperate end of the scale. At that point, they completed the computer task a final time before relieving themselves.

Though subjects' accuracy on the simple task never decreased, those who most urgently had to pee were slower to decide whether a card matched the one before it. There were only eight people in this study, so results should be interpreted with caution. But the researchers say that the slowed reaction time they saw was comparable to the effect of pulling an all-nighter, or having a BAC of .05%. If you're on the road and need to go, maybe you shouldn't wait too long to pull over.

The second Ig Nobel winner used larger study groups and asked how the need to pee affects our impulse control abilities. The researchers started with a classic Stroop test, in which color words are printed in contradictory ink hues:

It's easy for us to read the list aloud, but harder to go through the list and name the color of each word. That's because we have to suppress our first impulse, which is to just read what's there. The researchers gave subjects a Stroop test, then asked afterward how badly their subjects had to pee. All the subjects performed equally when reading the words. But when it came to naming the color of each word, subjects who reported a greater need to urinate were faster.

The researchers say that inhibiting our motor reflexes--in this case, inhibiting the urge to pee--helps us to simultaneously inhibit other urges. They tested their hypothesis in a few other ways. In one experiment, they first made sure half their subjects needed to pee by giving them 700 ml of water and waiting 45 minutes. Then subjects answered a series of questions about rewards: for example, would you rather have $16 tomorrow, or $30 in five weeks? Full-bladdered subjects were more likely to choose a larger reward in the future. The result was the same when, instead of drinking water, subjects filled out a word search that included a lot of terms such as "toilet" and "bladder." After being "primed" in this way, not only did subjects feel like they had to use the bathroom; they also tended to opt for the larger and more distant reward.

By happy coincidence, the name for this phenomenon is "inhibitory spillover." An effort at inhibition in one part of the brain leaks out to other areas. In this study, restraining themselves physically makes people more restrained in their decisions. Why take the smaller amount of money now, a subject reasons, when the reward will be bigger in the future? By then, maybe this burning feeling in my bladder will even be gone!

Exploring how people inhibit their impulses might teach us how to make better, or at least more forward-thinking, decisions. Should we take a small reward now, or hold out for something better? Should we accept $10 today for participation in a scientific study, or be free to use the bathroom whenever we like? The two studies seem to reach different conclusions about how the urge to "void" affects our cognitive processes, but really they're asking different questions. Taking them together, you might say that having a full bladder is a bad time to drive a car--but not such a bad time to buy one.

Lewis, M., Snyder, P., Pietrzak, R., Darby, D., Feldman, R., & Maruff, P. (2011). The effect of acute increase in urge to void on cognitive function in healthy adults Neurourology and Urodynamics, 30 (1), 183-187 DOI: 10.1002/nau.20963

Tuk, M., Trampe, D., & Warlop, L. (2011). Inhibitory Spillover: Increased Urination Urgency Facilitates Impulse Control in Unrelated Domains Psychological Science, 22 (5), 627-633 DOI: 10.1177/0956797611404901