Do Voters Prefer Lower Voices?

In apparent bad news for squeaky-voiced politicians, researchers at McMaster University say that voters prefer male candidates who speak at a lower pitch. In better news, their study involved no actual voters or candidates. So is it just laboratory lore, or is there some truth to this theory?

The study consisted of two experiments. In the first, 125 young men and women listened to a series of audio clips. The clips were taken from archived recordings of nine U.S. presidents, tweaked to create both a lower-pitched and higher-pitched version. In each trial, a subject listened to the two versions of one president's voice, then answered questions: Which of the two voices sounds more attractive? Which sounds more intelligent? Which would you be more likely to vote for?

The subjects chose the lower voices for all nine questions about positive attributes, and only selected the higher voice as that "more likely to be involved in a government scandal." But all this really says is that when subjects were presented with two recordings of the same person's voice, side-by-side, they consciously preferred the lower-pitched version.

To really get at people's voting preferences, the study should have kept subjects in the dark about what they were selecting. The audio clips should have been randomized so that subjects were comparing different people, not different versions of the same voice. The words spoken in each recording should have been the same. Naturally pitched voices could have been included, instead of only altered voices. As long as voices were being altered, it would have been nice to include several different pitches, instead of only two. And as long as we're changing the study altogether, how about some historical data about the voices of winning and losing candidates in actual elections?

The second experiment was a little better. Instead of presidents, subjects heard the voices of six non-famous males, manipulated into higher- and lower-pitched versions, speaking the same sentence. (Don't get too excited; there were only 40 subjects this time.) In each trial, subjects heard one raised voice and one lowered voice, then chose which one they would rather vote for in a national election.

Again, subjects picked the lower voices. But again, subjects were being asked to choose between an obviously lower and higher voice. If the voices had been presented one at a time, and subjects asked to rate them individually on attractiveness or leadership or appeal to voters, we could glean more information about people's unconscious preferences. As it is, we only know that subjects consciously preferred men with lower voices, deeming them better leaders and (according to attractiveness ratings) better potential mates.

Lead author Cara Tigue suggests that since a lower voice in males corresponds to higher testosterone levels, people who prefer basses to tenors are really displaying a preference for hormone-heavy men. Perhaps, Tigue says, we've evolved to prefer dominant men, and to detect them based on their vocal pitch.

It would be hasty, though, to infer anything from this study about the evolution of democratically elected pack leaders. Maybe if we elected more female politicians, people would stop associating a low voice with leadership ability in the first place.

Meanwhile, as Tigue acknowledges, there are a lot of factors that matter more to an election than vocal pitch. This year's candidates would be better off worrying about their talking points than the pitch at which they're delivered.

Cara C. Tigue, Diana J. Borak, Jillian J.M. O'Connor, Charles Schandl, & David R. Feinberg (2011). Voice pitch influences voting behavior Evolution and Human Behavior


Image: Screenshot from www.ricksantorum.com/video

Hell Hath No Fury like a Hermaphrodite Shrimp

Like car wash attendants for the coral-reef crowd, Lysmata shrimp staff "cleaning stations" where fish can go to be shined up. At these stations, cleaner shrimp eat parasites and dead tissue off the bodies of their clients, while the fish repay the act by not eating the shrimp. Some cleaner shrimp species, such as L. amboinensis, live and work in monogamous, hermaphroditic couples, faithfully fertilizing each other's eggs during their off-hours. In order to arrive at these peaceful unions, however, they might have to do a little killing.

Researchers Janine Wong and Nico Michiels in Germany wanted to know how L. amboinensis ends up in pairs rather than groups. When everybody has all the equipment necessary to spawn more shrimp, why is two the best number to live in?

The researchers collected cleaner shrimp subjects and kept them in tanks one, two, three, or four at a time.  No matter how many roommates they had, all the shrimp were given plenty of food and an equal amount of space. Then the researchers sat back to watch.

After six weeks, they found that every group of three or four shrimp, without exception, had become a pair of shrimp. Every pair of shrimp had remained a pair. To get rid of extraneous mates, the shrimp had killed each other until there were only two left.

Since the researchers had grouped the animals by similar size, though, no shrimp could just walk up to another and tear its head off. They had to wait for an opportunity.

Like other arthropods, cleaner shrimp periodically molt, shedding their old exoskeletons and growing new, better-fitting ones. Right after molting, which happens overnight, they're soft-bodied and vulnerable. In the experiment, the cleaner shrimp acted benignly toward each other during the day--but whenever the researchers returned in the morning to find a dead shrimp, its just-molted shell was in the tank with it. "Analysis of nighttime videos," the authors write, "indicated that aggressive interactions [had] contributed to mortality events."

Perhaps sensing the danger, shrimp living in groups of three or four suppressed molting, shedding their exoskeletons less often than usual. Once they were in stable pairs, the shrimp could relax and return to a regular molting schedule.

Competition for food could be behind L. amboinensis's urge to live in pairs. The more shrimp occupy a cleaner station, the fewer parasites and dead fish scales there are to go around. Having just one partner gives shrimp the minimum requirement for reproducing and the maximum share of food.

Another theory, called sexual allocation, says that species will find the optimal balance of males and females. This is true of male and female individuals within a population, as well as male and female functions within a hermaphroditic individual. Generally speaking, sperm are cheap for a body to make, while eggs are expensive. This means that a hermaphrodite should invest as much energy as possible into making eggs. If a shrimp is competing with others to reproduce, it'll have to make a lot of sperm to maximize its chances of fertilizing some eggs. But if a shrimp only has one partner, it knows its sperm have no competition--so it can get by with the minimum investment in sperm, and devote more energy to eggs.

The authors point out that the shrimp murders they witnessed took place under unnatural circumstances. On a real coral reef, cleaner shrimp getting bad vibes from their neighbors might just move away, rather than wait to be killed in the night. In enclosed laboratory tanks, the shrimp were forced to take drastic measures to reduce their group numbers. Still, the story ended the same way in all 20 tanks containing extra shrimp; this suggests the impulse to kill didn't come out of nowhere.

It's possible that in the ocean, the shrimp rarely (or never) act on their murderous tendencies. But someone would have to put cameras in the coral reefs to find out whether Lysmata's life is as much of a soap opera as it seems.

Image: Wikimedia Commons/Chris Moody


Janine W. Y. Wong, & Nico K. Michiels (2011). Control of social monogamy through aggression in a hermaphroditic shrimp Frontiers in Zoology


This post has been submitted to the NESCent contest for a travel award to attend the Science Online 2012 conference.

Make Mine Well-Done (with a Side of Calories)

Unless you enjoy your beef patties uncooked and straight from the fridge, there may be more calories hiding in that hamburger than you think. Harvard researcher Rachel Carmody says that our standard method of measuring calorie content doesn't account for the ways heat changes food. Cooking adds calories, Carmody says, and she's got some Atkins-adherent mice to back her up.

The calorie numbers on food labels are calculated according to how many grams of fat, carbohydrate, and protein the food contains, and how calorie-dense each of those nutrients is. It's simple math and chemistry. But since calories are a unit of energy--how much energy you, as an eating animal, manage to extract from your meal--biology should be a part of the equation, too. Our standard calorie math doesn't consider how much energy we expend chewing and digesting our food, or what components of our meal go toward feeding our gut microbes instead of our bodies. It also ignores the effect of cooking: heat breaks down starches and unravels proteins, making those molecules easier for our bodies to absorb.

Carmody used mice to study the effects of an all-cooked or all-raw diet. Mice, like humans, are natural omnivores. Unlike humans, they will allow you to feed them nothing but raw sweet potato for four days.

Adult male mice were put on a diet of either sweet potato or beef, raw or cooked. (The researchers also studied the effect of pounding the food, which makes it easier to chew but doesn't otherwise have much effect.) The mice could eat as much of their one food as they wanted. They were also free to exercise, running on magnetic wheels that recorded how much use they got. The researchers measured how much food their subjects ate, how much they exercised, and how much weight they had gained or lost after four days.

Since previous research had shown that cooked starches provide more energy, the potato-eating mice were expected to get more calories from their food when it was cooked. Obligingly, the mice maintained their original weights on a cooked-potato diet but lost weight on a diet of raw potato. Besides getting more energy out of each bite of food, the cooked-potato mice also ate more. The raw-diet mice, on the other hand, apparently weren't able to choke down enough sweet potato to keep up their weight. Both groups of mice exercised the same amount.

Mice being fed lean beef were also expected to lose weight, lacking necessary fat and carbohydrates in their diet. (The authors point out that in humans, eating nothing but lean meat leads to a condition called "rabbit starvation." You can go ahead and cross that all-rabbit diet off your list of resolutions for 2012, because it's said to cause diarrhea, headache, and "vague discomfort.")

All of the meat-eating mice lost weight. But those mice eating cooked meat lost significantly less weight, demonstrating that they were able to get more calories out of their food. Their amount of exercise was the same as the raw-meat mice. And unlike the mice fed on sweet potato, the meat-eating mice actually ate less of their food when it was cooked. This suggests that they weren't enjoying their diet very much, but it also suggests that the cooked beef was even more calorie-rich than the weight results would imply. If the mice eating cooked beef had swallowed the same quantities as their raw-diet counterparts, they might have lost even less weight, or not lost weight at all.

There are several factors that could make cooked meat more energy-rich. High heat unwinds (or "denatures") protein molecules, making them easier to digest. Since cooked meat is usually softer, we need to expend less energy chewing it up and breaking it down inside our bodies. Additionally, cooking kills the pathogens that like to hang out on raw meat. When we ingest E. coli or Salmonella along with our meal, we have to divert extra energy to our immune systems to keep those bacteria at bay. Calories spent chewing, breaking down, or disinfecting our food cancel out the calories of energy we're taking out of it.

We started using fire at least 300,000 or 400,000 years ago. For reference, that's before modern humans even existed. As long as we've been Homo sapiens sapiens, we've lived with fire. Once we figured out how to cook our food, which included a lot of meat, we would have seen the benefits: more energy for making tools, raising families, and growing those big brains.

Now that meat is available to many of us in the form of daily Double Whoppers, and not just the occasional mastodon steak, the question of how many calories are really in our food isn't a trivial one. Even the most careful calorie counters may be taking in more energy than they think. A fast-food taco, or a trough of starchy pasta at a restaurant, could hold even more calories than the menu says.

We need better math, for everyone's sake. For starving and malnourished populations, understanding how cooking increases calorie content could help people glean more sustenance from their limited resources. For populations struggling with obesity, better food labeling could allow people to take control of their calorie intake before we all have to go on a rabbit diet.


Carmody, R., Weintraub, G., & Wrangham, R. (2011). Energetic consequences of thermal and nonthermal food processing Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1112128108


Image: Carmody et al. 10.1073/pnas.1112128108

Which Ancient Megafauna Did We Wipe Out?

If things had turned out differently in past millennia, modern-day animal lovers wouldn't have to fly to Kenya to go on safari. North America was once overrun with tourism-worthy animals: Aside from the iconic woolly mammoth, there were saber-toothed cats, giant sloths, and short-faced bears more than twice as massive as a grizzly. We're still not sure what happened to them, but a new study in Nature attempts to untangle the whodunnit.

Since dozens of these "megafauna" species disappeared from the Americas, Eurasia and Australia just as humans were arriving, it's tempting to blame ourselves. The human love of the mixed grill, after all, runs deep.

But the mass extinction, beginning around 50,000 years ago, coincided with another key event: the end of the last ice age and shift to a warmer climate. So controversy over what killed off the ancient megafauna has persisted.

To tackle the large-scale, globe-spanning question, a large and globe-spanning team of researchers decided to take it species by species. Even though the animals went extinct around the same time, they might have been individually done in by different factors. The researchers looked at ancient animal remains and human remains from around the world, as well as DNA samples from the megafauna. The genetic material told them about each species' diversity over time (species with more genetic diversity are better able to adapt to changing environments), and the overlap of human and animal remains showed when and where we coexisted.

Woolly rhinoceros: Not our fault.

The study focused on just six animals. All of them were herbivores living in North America or Eurasia, and some of them have living members today but inhabit a greatly reduced range. 

The woolly rhinoceros, pictured above, used to live in Eurasia but is now extinct. The researchers found that the woolly rhino's population size was actually increasing well after the species came in contact with humans, and there's no evidence that we commonly preyed on (or even came in contact with) the rhino. This would seem to vindicate us--it was probably the warming climate, not humans, that wiped out the woolly rhinoceros.

Wild horse: Our fault.

The wild horse or tarpan, Equus ferus, is also extinct today (and not to be confused with wild populations of domestic horses). The species maintained a large Eurasian population well into the warming period, suggesting that climate change wasn't what ultimately killed it. The overlap between wild horse and human populations, as well as the abundance of wild horse remains at human archeological sites, hints that we may have hunted the species to death.

Woolly mammoth: ?

As for the poor mammoth, the data are disappointingly unclear. Our ranges overlapped in both Eurasia and North America, and ancient North Americans are known to have hunted the mammoth. But the mammoth's population in Eurasia, like the woolly rhino's, was still increasing after it came in contact with humans, and its range may have begun to shrink as the weather warmed. It could have been either culprit that ultimately killed the mammoth, or a fatal combination of human hunting and climate change together.

That fatal combination is what makes this sort of research--the cold cases of paleontology, if you will--urgent today. We're again experiencing warming, though it's happening much, much faster than in the age of the mammoths. Simultaneously, we're pushing species out of their habitats or poaching them into extinction. The authors of the new study didn't find any one feature, such as a genetic signature or a distinct pattern of distribution, that predicted which animals lived and which died. That means we're no closer to guessing which of today's species will survive climate change and human involvement--like the reindeer, which lived through the extinction of its fellow megafauna and thrives today--and which will go the way of the mammoth.

Images: PLoS/Mauricio Anton


Lorenzen, E., Nogués-Bravo, D., Orlando, L., Weinstock, J., Binladen, J., Marske, K., Ugan, A., Borregaard, M., Gilbert, M., Nielsen, R., Ho, S., Goebel, T., Graf, K., Byers, D., Stenderup, J., Rasmussen, M., Campos, P., Leonard, J., Koepfli, K., Froese, D., Zazula, G., Stafford, T., Aaris-Sørensen, K., Batra, P., Haywood, A., Singarayer, J., Valdes, P., Boeskorov, G., Burns, J., Davydov, S., Haile, J., Jenkins, D., Kosintsev, P., Kuznetsova, T., Lai, X., Martin, L., McDonald, H., Mol, D., Meldgaard, M., Munch, K., Stephan, E., Sablin, M., Sommer, R., Sipko, T., Scott, E., Suchard, M., Tikhonov, A., Willerslev, R., Wayne, R., Cooper, A., Hofreiter, M., Sher, A., Shapiro, B., Rahbek, C., & Willerslev, E. (2011). Species-specific responses of Late Quaternary megafauna to climate and humans Nature DOI: 10.1038/nature10574

Spiders Seek Balance of Work and (Fore)play

When picturing animals at play, you probably think of frolicking otters or wrestling tiger cubs--not arachnids aligning their copulatory organs. But University of Pittsburgh researcher Jonathan Pruitt believes that pretend sex between Anelosimus studiosus spiders is a form of play. And, like those wrestling cubs or human toddlers making block towers, the frisky young spiders are gaining skills that will help them in their adult lives. If they devote too much time to play, though, male spiders may never get to experience the real thing.

A. studiosus lives and builds its webs throughout North and South America. The males reach maturity first and leave their homes in search of females. Upon finding a juvenile female spider sitting in her web, a male moves in. While he waits for his love interest to reach sexual maturity, the claim-staking spider attempts to fight off any other males that come by.

But that's not the only activity that fills his time. The male and female engage in courtship and mock copulation--or, as Pruitt puts it, "non-conceptive sexual behavior." Though the female's genital tract is, physically, not open for business, she assumes a "receptive posture" and allows the male to place his parts next to hers.

Lest you suspect that the males are merely a little dim, and keep trying to mate despite the females' physical unavailability, Pruitt explains that mock copulation has clear differences from the real thing. For a start, the spiders are less aggressive with each other than during real sex. Additionally, mock copulation is much less likely to end with the male being eaten. In a real sexual encounter, the male has nearly a 1-in-4 chance of being cannibalized by the female before the deed is done. But males survive almost 99% of dry runs without becoming a meal.

According to Pruitt, this behavior meets criteria for animal play: it takes place in non-stressful situations; it happens frequently and voluntarily; it mimics a functional behavior but doesn't accomplish the same function. In this case, the function that's not being achieved is actual intercourse. But there are other benefits for the mock-mating spiders. Once they mature, pairs in which at least one individual is "experienced" get the job done faster than inexperienced pairs. This presumably helps the male's chances of not being eaten. Experienced males are also less likely to be rejected--or chased out of the web--by females. And experienced females, after they mate for real, lay sturdier eggs.

Pruitt and his colleagues wanted to know which spiders were most likely to engage in pretend copulation, and what the tradeoffs were for those spiders.

The researchers captured baby spiders and grew them to maturity in the lab. By pairing the spiders up and observing how much space they gave each other, the researchers could score each spider's "personality" as docile or aggressive. To study mock copulation, the researchers dropped male spiders onto the edges of female webs and watched each pair for a total of eight hours, counting how many pseudo-sexual encounters occurred. Finally, they dropped new (inexperienced) male spiders onto some of those webs and watched the ensuing face-offs between males.

They found that a spider's propensity for fake mating depended on several factors. Docile spiders were more likely to engage in mock mating when their female partners were large. That's not what one might expect from a species prone to cannibalism, but apparently the males are enticed by large females' greater egg-laying potential.

Among aggressive male spiders, on the other hand, female size didn't matter. Their likelihood of mock copulation only depended on whether their bodies were in good condition.

Aggressive males were also more likely to win competitions with other males, forcing intruders to retreat from their webs. But male spiders that had engaged in a lot of pretend sex, apparently worn out, were less likely to win these duels.

Thus, as Pruitt puts it, "males that engage in the behavior excessively risk exhausting themselves and being supplanted by cohabitating interlopers." (Words to live by.) Though females may mate with multiple males, the male that gets to her first will father most of her offspring. So getting kicked out of one's web by an intruder, even temporarily, can have a high cost.


Is mock copulation in spiders a form of play, or of practice? For animals, they may not be substantially different things. A definition of human play would have to include fun. But whether we're looking at a dolphin or an invertebrate, we can't truly know whether an animal is enjoying itself. Whatever the spider is doing, it's clear that pretend sexual encounters can increase its reproductive success and evolutionary fitness. Unless the male spends too much energy entertaining itself, of course, in which case it may never get to demonstrate its prowess.




Pruitt, J., Burghardt, G., & Riechert, S. (2011). Non-Conceptive Sexual Behavior in Spiders: A Form of Play Associated with Body Condition, Personality Type, and Male Intrasexual Selection Ethology DOI: 10.1111/j.1439-0310.2011.01980.x

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