Field of Science


The Composer and the Cassowary: An Appreciation of Mistakes

High in a church balcony last weekend, waiting to perform a solo for Palm Sunday and trying not to panic, I thought about cars being hit with hammers. I'm not sure this is the kind of visualization recommended for singers. But sometimes genetics asserts itself.

A college biology professor once told my class that genetic mutation is like whacking a car with a hammer. You will almost never improve your car this way. More often, you'll damage it. If you're lucky the damage will be only superficial: a change in the silent portion of your genome, or maybe a few funny feathers.

The piece my choir was getting ready to sing, Gregorio Allegri's Miserere, has experienced some mutations in its own DNA over the centuries. Allegri composed the piece way back in the early 1600s, and after that it was sung exclusively during Holy Week at the Sistine Chapel. Even though people had to attend a 3 AM service in Rome to hear it, the Miserere became famous. The Vatican, wanting to keep the piece to itself, threatened excommunication for anyone who copied down the score.

As secrets and life forms tend to do, though, the music leaked out. In the late 18th century, a certain precocious teenager with the last name of Mozart spent Holy Week in Rome with his father. After hearing the Miserere at the Sistine Chapel, young Wolfgang sat down and transcribed the whole thing from memory. He returned for a second performance to double-check his work. From there, the score got into the hands of a music historian who published it.

If the music had really been genetic material, Mozart would have been DNA polymerase, a molecular machine that copies DNA. The polymerase molecule grasps a DNA strand and crawls along, letter by letter, building a matching strand as it goes.

Like Mozart, the enzyme is good at what it does. It proofreads. But sometimes it slips up: A single letter of DNA might be swapped for another one. A section of the code might be flipped backward. One or more letters might be inserted or deleted. (Even one letter lost or gained can cause a major change, since the DNA code is read in three-letter words. In English, imagine losing a letter from the sentence "SHE ATE THE RED BUG" and ending up with "SEA TET HER EDB UG." Some words are still there, but the meaning of the sentence is destroyed.)

Even if DNA polymerase is performing well, damage to the genome can come from outside sources such as UV radiation. But a large fraction of your DNA seems to do nothing at all. If a mutation happens here, you won't know the difference. If a slip-up creates a synonymous change in a gene—the code allows for some words to be spelled in multiple ways—you'll also be fine. And if the mutation does something horrible, it will remove you from the gene pool.

Evolution doesn't care much about any of this. It only notices the rare constructive strokes of the hammer, and it only sees them if they happen in the cells that will become your sperm and eggs (called the "germ line"). If you have DNA damage in the skin of your back from too much tanning, you can't pass it on to your children.

Back when Allegri's Miserere was being sung in the Sistine Chapel, the choirs were made up of men and boys. In choirs like mine, women sing the alto and soprano parts. But that's only a superficial mutation; we singers are the flesh of the piece.

The germ line mutation came in the 19th century. Someone who copied the piece apparently made a mistake, shifting a whole repeated section up by a fourth. What started out as a normal soprano solo now rocketed all the way to a high C, a preposterous note that humans are almost never asked to sing.*

Natural selection didn't weed out this mutation. Once the change had happened and been passed to new generations of the musical score, it stayed in place—even after the error was discovered. We continue to sing the mutated piece because, simply, it's awesome this way. Here's a video. You'll know when the boy soprano hits the high C: it's the note you hear through the bones of your spine instead of your ears.

It's not an overstatement to say that what happened to Allegri's music represents the whole history of life on Earth. Every new development has come from a mistake, small or egregious, that was allowed to stick around for one reason or another. Life started as tiny blobs, then whoops—heads! Legs! Oops again—tulips! Uncorrected errors became tree bark, snail shells, lungs, fur, resistance to antibiotics. Inching along mistake by mistake, life forms developed the machinery to make blood, slime, deadly venom, and spider silk.

Some living things have come together so elegantly that they bring an audience to its feet. There are racing cheetahs, swooping owls, orchids that mimic bees. But even the giant, gut-colored flower that stinks like a corpse to attract flies is a success in its family line. The cassowary is a bird that made so many mistakes, it traded the ability to fly for tree-trunk legs and a head with a sail on top. Even the cassowary, though, is doing something right. Errors become the high notes.

Postscript: My choir director turns out to have a son who, at age three, actually took a hammer to the family car while it was in the garage. The car was not improved. 

Images: Top, cassowary from The New Student's Reference Work and Gregorio Allegri, both via Wikimedia Commons. Bottom, cassowary by Peter Nijenhuis via Flickr.

*Plot clarification, in case anybody is worrying about me up there in the loft: this is not the part I sang.

Good Coot Parents Let Kids Starve, Make It Up to Them Later

Too many mouths to feed? Just make your babies fight each other to the death! That's a strategy some bird parents have been using since even before The Hunger Games was popular. It means the strongest chicks get stronger while the weakest ones conveniently stop showing up to the table.

One type of bird takes this family drama a step further: after letting the biggest chicks bully their siblings for a while, parents suddenly decide the runts are their favorites and begin beating up the older chicks themselves. Authors looking for the next dystopian mega-hit, take note.

"Many species of birds show 'hatching asynchrony,'" says Daizaburo Shizuka of the University of Nebraska, Lincoln. This means they stagger the hatching of the eggs within a nest. When some chicks emerge from their eggs days later than others, the younger birds are doomed to be outweighed and outcompeted by their older siblings. Blue-footed boobies, for example, produce two mismatched chicks; one may peck the other to death or shove it out of the nest. (If you think that's horrifying, you haven't heard about sand tiger sharks, which eat each other inside their mother's womb.)

The polite way to say "letting half your babies die" is "brood reduction." Why hatch a runty egg at all? Parents may allow more siblings to live if food is plentiful. Or a second egg might be a kind of insurance in case the first doesn't hatch.

American coots are waterbirds that lay large clutches of eggs and may space out their hatching over a week or more. This means some siblings end up much heftier than others. At first, young coots follow their parents around, relying on their parents to feed them insects and plant material they find by diving. Siblings don't physically attack each other, but older birds easily out-jostle smaller ones for food. Half of all chicks die of starvation.

Over several years, Shizuka and Bruce Lyon, an ecologist at the University of California, Santa Cruz, monitored 75 American coot families on a lake in British Columbia. They snuck every new chick away as it hatched to give it a color-coded tag. Spying on these families while their chicks ate or starved, the researchers discovered a highly unusual system at work.

During the first 10 days after hatching, younger coot chicks often died of starvation. But any runty chicks who survived this period saw their luck turn around. Parents suddenly started playing favorites. Each coot parent picked one preferred chick out of those who'd hatched last, and gave that chick the most food. Heightening the drama, moms and dads each chose a different favorite.

To discourage bigger siblings from asking for so much food, the parents spent more time "tousling" these birds. In humans this means "affectionately messing up someone's hair," but in birds it means "grabbing your baby by the head and shaking it." As you might imagine, it's pretty convincing. The beefy siblings backed off.

Once parents switched to spoiling the runts and beating up the bigger kids, late hatchers became just as likely to survive as their siblings. The youngest chicks even grew slightly larger than their older brothers and sisters.

This system may be a way "for parents to try to get the best of both worlds," Shizuka says. First, coot parents allow brood reduction to happen, watching their chicks compete to the death. Once the family reaches its optimal size, he says, "parents can take matters into their own hands to make sure that the youngest chicks that are still surviving end up getting enough."

Don't throw out your parenting books yet. Although this method seems to work for the coots, scientists still aren't sure why so many birds have evolved elaborate strategies that require siblings to murder each other—or why chicks go along with it. Shizuka says, "It's safe to say the matter is not resolved."

Shizuka, D., & Lyon, B. (2013). Family dynamics through time: brood reduction followed by parental compensation with aggression and favouritism Ecology Letters, 16 (3), 315-322 DOI: 10.1111/ele.12040

Image: Bruce E. Lyon

Play Along as Sub Discovers Sunken Whale Bones Crawling with New Life Forms

Forget a needle in a haystack. For that search you'd be allowed light and air—and when you held the needle in your hand at last, it wouldn't be unrecognizably coated in bone-eating worms. Looking for whale skeletons on the ocean floor is such an impossible task that no one sets out to do it on purpose. The most recent find, lying near Antarctica and crawling with previously unseen species, was a very happy accident.

A dead whale that sinks all the way to the ocean floor is called a "whale fall," kind of like "windfall," which it is. The corpse is a massive sack of food dropped from above into a barren landscape. It feeds generation upon generation of life: first the scavengers that pick it clean, then other creatures that chew the bones into scaffolding and bacteria that churn out sulfides, and then a host of animals that feed on these chemicals directly or indirectly.

The same types of animals live at hydrothermal vents and cold seeps, where they consume sulfides and other chemicals seeping out of the earth. Whale falls may act as stepping stones for these species to migrate from one undersea chimney to the next. Even though they haven't seen many sunken skeletons up close, scientists have deduced this with the help of experiments such as dropping wood piles into the ocean and leaving them there.

When the members of a UK-funded research expedition came across the latest whale fall, they were piloting a remotely operated vehicle (ROV) more than 1,440 meters under the sea. "We were at the end of a very long ROV survey," says graduate student Diva Amon, "and had already gone an hour over our allocated time on the seafloor." Then, she says, "we spotted a row of curious white blocks in the distance."

Investigating more closely, the team realized that the blocks were spine bones. They were looking at a whale skeleton covered in deep-sea animals. "We all realized that this was only the sixth natural whale fall to be seen, and the first in the Antarctic," Amon says. "Everyone was thrilled."

In this video, you can watch from the eyes of the ROV as it pans across the find. The camera moves from the whale's skull to its vertebrae, which are lined up like a string of enormous marshmallows. Then it zooms in to see the lush jungle of life sprouting from each bone. Around 50 seconds in, you'll get a cephalopod surprise (is there a better kind?).

The fronds you see waving from the vertebrae are the tail ends of bone-eating worms called Osedax, which Amon calls "remarkable." Tucked in between them are the shells of limpets. When the camera pans down to a fellow who looks like a rubbery sock (a sipunculan worm), you might spot tiny crustaceans scurrying across the bone in the background. Did you see the worm whisk itself into hiding when the squid jetted by? You should probably watch again to be sure.

If the pale denizens of this skeleton look weird to you, they were weird to the scientists back at sea level too. The creatures at the whale fall included nine species that had never been seen before. "Every time one explores the deep sea, there is a very large chance of finding a new species," Amon says.

DNA analysis showed that the skeleton, nearly 11 meters long, once belonged to a minke whale. The types of creatures now living on it were similar to those at other whale falls. Based on these life forms and the state of the bones, scientists could tell that the whale fall has become a sulfur-rich environment. It houses the same animals that inhabit deep-sea vents and cold seeps, and it may be helping those creatures migrate across the ocean floor. "One species of limpet that was found on the whale bones was also found on nearby hydrothermal vents," Amon says.

The researchers couldn't tell whether the skeleton had been in its resting place for a few years or for several decades. Either way, they left this rare needle right where they found it.

Amon, D., Glover, A., Wiklund, H., Marsh, L., Linse, K., Rogers, A., & Copley, J. (2013). The discovery of a natural whale fall in the Antarctic deep sea Deep Sea Research Part II: Topical Studies in Oceanography DOI: 10.1016/j.dsr2.2013.01.028

Images: Whale vertebrae photo and video (c) UK Natural Environment Research Council ChEsSo Consortium; deep-sea creatures (c) Natural History Museum.

Need the Time? Ask a Rooster

"The connection with the sun coming up is a misconception," asserts an article in the rural lifestyle magazine Grit. "Roosters crow all the time." Some roosters in Japan would like to loudly disagree. They've shown scientists that their crowing has everything to do with what time of day it is—something they don't even need the sun to know.

Tsuyoshi Shimmura and Takashi Yoshimura, both of Nagoya University in Japan, investigated whether a rooster's crowing is tied to its circadian clock. That is, does the bird's internal sense of night and day determine when it's noisiest? Or do roosters crow at random hours—"morning, noon and night, not to mention afternoon, evening and the parts of the day that don’t have names," according to a disgruntled neighbor-to-roosters quoted in the Grit story?

Like any scientists studying how animals follow the sun's rhythms, the researchers began by shutting their subjects indoors. In a controlled environment, they kept the roosters on a strict schedule of 12 hours in the light and 12 hours in the dark.

Recordings showed that the roosters did not crow at random. A sudden burst of crowing came two hours before the artificial dawn, and the birds gave another "cock-a-doodle-doo" immediately after the lights came on. (Though in their country, the authors point out, it's "ko-ke-kok-koh.")

Then the scientists turned the lights out entirely, keeping the birds in a permanent night. The roosters at first continued to follow crowing cycles of roughly 24 hours, with only their internal clocks keeping them on schedule. Over the course of two lightless weeks, this rhythm gradually wound down.

In the barnyard, though roosters need their circadian alarm clocks for any pre-dawn crows, they can rely on other cues to trigger their crowing at sunrise—say, the sun. So Shimmura and Yoshimura next checked whether light itself causes crowing.

Starting with roosters that were living in permanent night, they tried exposing the birds to a little bit of light at the dawn hour. A few of the roosters crowed. When the researchers used brighter and brighter light, more and more of the birds crowed in response, as if recognizing the sun. A sound recording of other roosters crowing also worked to set their birds off.

Yet just flipping on the lights wasn't enough to make a benighted bird start crowing. When the light and sound signals came at "dawn," the roosters readily responded. When researchers used the same signals later in the "day," their birds didn't respond as strongly. And when they tried the signals at "night," the roosters didn't crow at all.

Even though they were living in permanent dark, roosters weren't fooled by seeing a fake sun at any old time. To get them crowing in earnest, the signals of sunrise had to come at the same time that the birds' bodily alarm clocks rang.

Roosters seem to be expert timekeepers. This knowledge, though, may not make come as much consolation to their neighbors.

Shimmura, T., & Yoshimura, T. (2013). Circadian clock determines the timing of rooster crowing Current Biology, 23 (6) DOI: 10.1016/j.cub.2013.02.015

Image: by -JvL- (Flickr)

Why People on Cell Phones Are the Worst

If it were urgent, maybe we could be more forgiving. But the subject of that phone call one table away at Starbucks never seems to be vital. A bathroom renovation, maybe. Or a phrase-by-phrase recounting of a text message dialogue with an ex. If you suspect overheard phone conversations are inherently more awful than people talking face to face, you're right: research shows that these conversations reach across our espresso cups, grab our attention, and don't let go.

Psychologist Veronica Galván studied this problem recently at the University of San Diego. To bring the coffee shop into the lab, she started by lying to about 150 undergrads. The students believed themselves to be in an experiment about reading comprehension. When they sat down at a table to solve a worksheet full of anagrams, another student sat down next to them and launched into a seven-minute conversation. This person, of course, was a plant.

The neighbor had a scripted conversation, either over the phone or with a second actor in the room. (The discussion covered three typically scintillating topics: "a birthday party for dad, shopping for furniture, and meeting a date at the shopping mall.") Meanwhile, subjects tried to ignore the noise and dutifully completed their worksheets.

When subjects filled out questionnaires afterward about how distracting they'd found the conversation in the room, their answers depended on what they'd heard. People who heard the one-sided conversation (a person on a cell phone) found it significantly more noticeable, more distracting, and more annoying than those who heard two people talking.

Even so, all the subjects performed about the same on their anagram-solving test. Galván had expected to see a difference between people who heard a phone conversation and people who didn't, but she says the anagrams may have been too easy to show an effect. Conversely, they may have been too difficult to allow people's attention to wander. Galván hopes her future experiments will reveal what kinds of tasks are most vulnerable to distracting phone conversations.

After their anagram test, subjects took a pop quiz about the conversation they'd just overheard. They saw a series of words and had to decide whether each one had been spoken in the conversation. In this case, the test results were clear. People who'd heard a one-sided conversation remembered it better than people who'd heard a two-sided conversation, Galván reports in PLOS ONE. Additionally, they rated their confidence in their responses higher than people who heard the two-sided conversation.

It's possible people remembered two-sided conversations less clearly because they heard more words overall. But the idea that a one-sided conversation seizes more of our attention agrees with previous research on the subject.

Because we can follow along with a two-sided conversation, its content is more predictable and therefore (the theory goes) easier to ignore. One person yakking away into a phone, however, is unpredictable and confusing. We can't stop our minds from trying to puzzle it out.

The subjects in Galván's study were all undergraduates. "College students are fairly accustomed to overhearing cell phone conversations," she says. "Yet even they reported more annoyance and had better memory for the one-sided conversation." She suspects older adults might find cell phone conversations even more annoying and distracting than college students do.

Until science finds a way to make other people's phone calls less bothersome, you're doomed to catch every word of that half-a-business-meeting being conducted two chairs over. On the bright side, you may remember it well enough to blackmail the guy in the future.

Galván, V., Vessal, R., & Golley, M. (2013). The Effects of Cell Phone Conversations on the Attention and Memory of Bystanders PLoS ONE, 8 (3) DOI: 10.1371/journal.pone.0058579

Image: Ed Yourdon (Flickr)

Bats, like Batman, Thrive in a Post-Apocalyptic Environment

Without plagues, earthquakes, and unhinged criminal masterminds, the residents of Gotham might never need to put up the bat signal. Real bats, of course, are less concerned with responding to emergencies than with eating bugs. But like Batman, they do just fine—if not better than ever—in recently devastated environments. Specifically, forests that have burned down.

For five weeks in the summer of 2002, a wildfire tore through national forests in the Sierra Nevada mountains. The McNally Fire was started by a careless human, and ended with over 150,000 acres burned. A year later, scientists came by to see how the bats were doing.

"Bat ecologists have known for a while now that bats respond favorably to controlled, low intensity fires," says Michael Buchalski of Western Michigan University, one of the study's authors. "We were more interested in the effects of large, natural fires." These blazes can completely destroy the forest canopy, leaving an area unrecognizable.

Researchers visited 14 sites in the woods, half in burned areas and half in areas that were untouched. They left devices that recorded the ultrasonic cries of echolocating bats at night. Since tallying up all the bat activity they heard could be misleading—one flourishing species of bats might mask the disappearance of another—they divided the recordings into groups of similar-sounding calls, representing groups of bat species.

The researchers estimated how plentiful each type of bat was based on how often they heard its calls. Comparing burned and unburned areas, they found that no bat group was bothered by the fire. Instead, every group of bats was at least as plentiful in the fire-scorched areas—and some were doing even better than usual.

Despite the absence of costumed criminals, a few factors might account for bats' increased activity in a scorched landscape. Bats hunt by swooping through the air and searching for insects below. With much of the vegetation cleared out by fire, insects have fewer places to hide, and hunting bats have a clearer view for their echolocation.

Additionally, the first plant regrowth after a fire leads to a boom in insect species. This means there's more prey than ever available for hungry bats. "One-stop shopping!" says coauthor Joseph Fontaine of Murdoch University. Those bats may find new places to roost—or, if you prefer, build their secret lairs—inside dead trees.

Buchalski and Fontaine say bats probably need a mix of landscapes to thrive, including areas that have recently burned. Carefully allowing forests to burn more like they did in the past could lead to "healthier forests and healthier wildlife populations," Buchalski says. "However, this is a very contentious issue within the field of forestry management."

"We have spent the majority of the last century suppressing and excluding fire," Fontaine adds. "More fire right now is probably not a bad thing whatsoever." (For non-human animals, anyway.) With climate change increasing the potential for drought and wildfire, the authors say that understanding how different species deal with fire is becoming more important.

Bats aren't the only animals that appreciate a fire. Fontaine says deer mice and other short-lived rodents respond very well to fire, and deer and elk like to chew on the soft new shrubs that have regrown a few years later. Several types of woodpeckers, he adds, rely on fires. Many bird species that forage in the open and don't need living trees to make their nests have a similar response to the bats.

Although forest fires are a boon for many species, the robin doesn't seem to be among them.

Buchalski, M., Fontaine, J., Heady, P., Hayes, J., & Frick, W. (2013). Bat Response to Differing Fire Severity in Mixed-Conifer Forest California, USA PLoS ONE, 8 (3) DOI: 10.1371/journal.pone.0057884

Image from public domain files at Wikia.

Rats Sniff to Communicate, Not Just to Smell

There's more to a pair of rat noses than meets the eye. Like tiny, leashless dogs, rats like to sniff each other all over when they meet. Yet not all of this sniffing is aimed at gathering scents. Some of it seems to transmit messages such as "I'm in charge" or "Be cool" or "Please don't bite my face."

Rats and other animals give off odors from the "face, flanks, and anogenital region," says neuroscientist Daniel Wesson of Case Western Reserve University. So it's not surprising that these regions are where rats aim their sniffers when they cross paths. To find out whether there might be more going on, though, Wesson outfitted rats with head-mounted devices that measured the speed of their sniffs. Then, after recording videos of these rats encountering each other, he looked at how sniff frequency lined up with different stages of the rodents' interaction.

He saw that all rats sped up their sniffing when their noses were pointed at each other's flanks or rear ends. But when the rats were sniffing each other's faces, their behavior depended on whether they were socially dominant or subordinate. Higher-ranking rats sped up their sniffing as usual. Lower-ranking rats slowed down their own sniffing in response.

This seemed to be an "appeasement signal," akin to climbing into one's own locker when the school bully approaches. Wesson found that when subordinate rats didn't give this signal—when they kept up their sniffing at the usual rate—dominant rats were quicker to pick a fight.

To further test this idea, Wesson treated the insides of the rats' noses with zinc sulfate, making them temporarily lose their sense of smell. Even though they weren't gathering any odors, rats kept on sniffing. And when they were face-to-face, they acted the same as always: dominant rats sniffed faster, while subordinate ones slowed down to avoid trouble. "This sniffing behavior was interestingly resilient," Wesson says.

Sniffing seems to be a form of communication for rats—but only sniffing in the face, not other body parts. Wesson says this may be because face sniffing is an especially vulnerable position for a rat or other animal to be in. When their eyeballs and whiskers and biting parts are all in close proximity, maybe it's a good time for rats to make clear that they don't want a fight.

Alternately, face-to-face might be the only way a rat can detect another rat's sniffing; maybe the signal wouldn't get through if it were aimed at the tail end. "These are different theories we are testing now," Wesson says. There may also be ultrasonic squeaks or other signals invisible to humans that contribute to the conversation between two rats.

If rats use sniffing for communication, and not only for gathering smells, do other social sniffers do the same thing? "I would predict so," Wesson says. "Other rodents likely use this behavior, as could possibly cats and dogs." He points out that neighborhood dogs who meet on a walk will sniff each other, then either part peacefully or start fighting. Some signal in their sniffing behavior may make the difference, though this idea would have to be tested.

That's not to say dogs or rats aren't also gathering actual smells when they sniff. It would be "frankly silly" to discount the importance of smell in an animal's life, Wesson says. It seems there's much more going on, though, when an animal sticks its nose into the world.

Wesson, D. (2013). Sniffing Behavior Communicates Social Hierarchy Current Biology DOI: 10.1016/j.cub.2013.02.012

Image: Daniel Wesson.

The Evolution of Humans and Lice in 13 Reality TV Titles

Humans and our lice are even closer travel companions than Kourtney and Kim when they took New York. The parasites cling to us more tightly than Paris Hilton's new BFF. They've been such cozy acquaintances of ours, in fact, that the story of human evolution is written into their genes.

That's what Marina Ascunce and other researchers at the University of Florida found when they sampled lice from around the world and compared their DNA. In the chromosomes of these wingless bloodsuckers, they discovered a window on human culture almost as good as a flip through the TV guide.

Fear Factor
"Lice" is a four-letter word that can inspire dread in the hearts of kindergarten teachers, moms and dads, and well-coiffed middle schoolers. An infestation of head lice is usually harmless, if horrifying. Ascunce and her coworkers point out, though, that head lice in the United States, Nepal and Ethiopia have been found carrying disease-causing bacteria.

What Not to Wear
More dangerous than head lice are body or clothing lice, which mostly affect the homeless and people living in refugee camps. These lice can carry at least three kinds of bacteria that are dangerous to humans. Over the past few decades, the authors write, there have been several disease outbreaks tied to body lice—including an outbreak of epidemic typhus (caused by the bacterium Rickettsia prowazekii) in Burundi that sickened more than 45,000 people.

Body and head lice belong to the same species (Pediculus humanus). Yet the two subspecies, like knockoff shows on different TV channels, make up separate populations that don't encounter each other in nature.

The Pickup Artist
The researchers used lice that had been plucked off of humans in 11 locations around the world. Head lice came from a few sites each in the United States, Asia, and Europe, plus Honduras. There were also body lice from Nepal and from a homeless shelter in Canada, for a total of 93 lice.

The Bachelor
Incidentally, head lice infestations usually include more females than males. It's not clear why, but when you have lice, your scalp is like one big rose ceremony.

House Hunters International
By letting them stow away in our hair while our own species migrated around the world, we've created unique geographic populations of lice. The head lice in this study fell into into three distinct groups based on their shared DNA. Asian lice (from Thailand, Nepal and Cambodia) made up one group. Lice from Honduras were another distinct group. Lice in the United States, though, were in the same genetic cluster as those from Europe.

Temptation Island
Louse DNA shows plenty of evidence of inbreeding. This isn't too surprising when you consider that populations reproduce as fast as they can while staying marooned on one person's head (and that new infestations can result from just one egg-bearing female crawling onto a fresh scalp). The most-inbred lice were found in New York.

19 Kids and Counting 
Compared to their highly inbred head cousins, body lice showed a little more diversity. One reason for this, the authors point out, may be that body lice have more young. A female head louse can leave 150 eggs nestled and glued into her host's hair; a female body louse may leave twice that many eggs in the seams and hems of a person's clothing.

MXC: Most Extreme Elimination Challenge
Another factor that has probably contributed to low diversity in lice populations is our ongoing effort to kill them. Head lice infestations have increased around the world, the authors write, in part because the bugs have developed resistance to the insecticides we dump on kids' heads. A dousing with poison may leave behind a few hardy lice, which can then repopulate the whole area. (Biologists call this kind of population narrowing and regrowth a "bottleneck.")

Britain's Worst Celebrity Driver
Actually it has nothing to do with lice, but did you guys know this was a real show?

The Real World: Boston
The American lice sampled by Ascunce and her colleagues (from New York, San Francisco, and Florida) were a genetic match to the European lice (which came from Norway and the United Kingdom). If this pattern holds up across the United States and Europe, it would suggest that the lice Americans carry traveled to the New World along with European colonists. In other words, we have Columbus's lice.

Sarah Palin's Alaska
The genetically distinct lice found in Honduras, though, don't seem to have come over with the pilgrims. The authors think it's possible that the Honduran bugs represent the native American lice. Perhaps they came here on the heads of more ancient humans who crossed into this continent from Asia, traveling across the Bering Strait and down through Alaska long before Europeans arrived.

Wife Swap
An earlier study of louse mitochondrial DNA (genetic material that's only passed through mothers) turned up a distinct genetic group that's present in Europe, Australia, and the New World, but not in Africa. It's possible that this DNA, rather than having come from the lice our most ancient ancestors carried out of Africa, represents lice those humans picked up while hobnobbing with Neanderthals on their way through Eurasia. 

Survivor: Heroes vs. Villains
The story of our conflict with lice is a classic one. As long as the insects keep developing resistance to our poisons and fighting back when we try to kill them, this series isn't likely to ever get canceled.

Ascunce, M., Toups, M., Kassu, G., Fane, J., Scholl, K., & Reed, D. (2013). Nuclear Genetic Diversity in Human Lice (Pediculus humanus) Reveals Continental Differences and High Inbreeding among Worldwide Populations PLoS ONE, 8 (2) DOI: 10.1371/journal.pone.0057619

Image: Gilles San Martin (via Wikimedia Commons)

This post has been submitted to the 2013 blog contest held by the National Evolutionary Synthesis Center (NESCent).