Field of Science


The Plus Side of Eating Placenta

He's not suggesting new parents pause in the delivery room to whip up a placenta sandwich. But neuroscientist Mark Kristal says human mothers might be missing out on the benefits other mammals receive from gobbling up their afterbirth. With luck, there might be a way for us to take advantage of placenta power that's not totally disgusting.

Mark Kristal is a professor at the University of Buffalo who's been studying the practice of placenta eating--or placentophagia, if you want to bring it up in polite company--for more than 40 years. His interest in the subject sprang from his study of maternal behaviors in mammals giving birth. "I had the field to myself," he said in an email.

And he knows it's gross. "Unfortunately, people often ask me what my research is on during dinner," he says. "It always gets a laugh (and a gag)."

Humans, with the exception of some naturopaths and celebrities, don't eat placentas. But that makes us nearly alone among mammals. From rodents to cattle to apes, new moms turn to the business of eating or licking up the afterbirth, including the liver-like placenta, as soon as the baby is out.

In a new review paper (soon to be available here), Kristal and his coauthors discuss the potential benefits of placentophagia for mammals that practice it, as well as for mammals that don't (us). There are several practical reasons why animals might ingest their placentas. Maybe they want to hide the odor of blood from predators, for example, or to keep their nests clean. Maybe mothers are famished after the ordeal of giving birth, or perhaps the placenta replaces nutrients that were depleted during pregnancy.

Though some of these explanations fit subgroups of mammals, none of them works universally. So Kristal thinks there must be a more basic evolutionary explanation for placentophagia. If almost every mammal does it, the simplest explanation is that they do it for the same reasons.

One intriguing possibility, and the strongest lead researchers have so far, has to do with pain. In the 1980s, researchers discovered that female mammals' bodies produce pain-relieving endorphins during labor and delivery. Studying rats, Kristal found that eating the placenta increased the effect of these endorphins. The placenta didn't dampen pain on its own. But rats that ingested placentas felt less pain, because they responded more strongly to their bodies' own pain relievers.

The effect also works with morphine, a similar pain suppressant. Rats that ate placenta, or amniotic fluid, experienced greater pain relief from morphine. Kristal found that the pain-relief-enhancing effect of afterbirth works in male rats, too, and in animals of other species. It also worked when researchers fed rats with human placentas.

This suggests human placentas have the same health benefits as other mammals'. So why do humans, alone among land mammals, deny ourselves the pleasures of eating placenta? It's possible, Kristal says, that evolution destroyed our appetite for afterbirth for a good reason. Maybe it has to do with toxins caught in the placenta as the organ filters them out of the fetus's environment. Or maybe extra-painful childbirth was helpful in human evolution because it encouraged women to help each other through delivery.

Kristal thinks that with further research, scientists can identify the ingredient in placenta that enhances pain relief from morphine or endorphins. Then the compound can be made in the lab and used as a drug--for all kinds of pain in males and females, not just childbirth.

These days, a few women who have gotten wind of the potential advantages of placentophagia are experimenting with it themselves. But they're interested in more than just pain relief. There are claims that eating one's placenta cures conditions ranging from postpartum depression to nursing difficulties.

Though such claims aren't backed up by any research, Kristal is interested in these same postpartum problems--which, he says, are uniquely human. Sure, other mammals sometimes go so far as to kill and eat their newborns. Rodents, for example, are tempted to ingest everything that comes out of them during delivery, baby included. But a healthy newborn will get its mother's attention by moving around and making noise. Other mammals only eat their young after an extremely stressful pregnancy.

Kristal says none of these behaviors, though, are parallel to the human problems of postpartum depression or an inability to bond with one's baby. If scientists could pinpoint the mechanisms that cause these issues, they could then start asking whether any element in the placenta might help treat them.

While science lags behind, eager placenta-eaters are going ahead with their own methods. Actress January Jones recently outed herself as a fan of placenta pills. After delivering her son, she had her placenta dried and made into capsules. Pill poppers are also featured in this gruesomely detailed 2011 New York Magazine article about placentophagia. (Focused on trend-conscious Brooklynites, the story contains the horrifying sentence, "I threw a chunk of placenta in the Vitamix with coconut water and a banana.")

Mark Kristal gets emails "all the time" from women who have tried placentophagia, he says. Without exception, they all insist it helped them.

But the claims of placentophagia fans are the same regardless of how much placenta they ingested, when they took it, or how they prepared the organ (cooked? raw? encapsulated? smoothied?). And it's unlikely that any real medicinal effect of the placenta could be so universal. For example, experiments have shown that placenta loses its pain-suppressing power when it's heated.

It's more likely that the benefit human women report from eating their afterbirths is the benefit of placebo. The ability to make women feel that they're tapping into a primal force to keep themselves healthy may be the real power of placenta.

Mark B. Kristal, Jean M. DiPirro, & Alexis C. Thompson (2012). Placentophagia in Humans and Nonhuman Mammals: Causes and Consequences Ecology of Food and Nutrition

Image: avlxyz/Flickr (Note: This is a picture of someone's French toast remains. Not placenta.)

Adorable Lemur's Sordid Nightlife Revealed by Lice

How do you study the social habits of an animal that's shy, comes out only at night to scurry through tree branches in dense jungles, and is the size of an M&M packet? You could try talking to its body lice.

The brown mouse lemur (Microcebus rufus) is an almost supernaturally adorable primate that lives in Madagascar. Thanks to its tininess and hard-to-access habitat, scientists don't know much about its behavior. So to get the scoop on the lemur's social life, a group of researchers turned to the lemur's less adorable companion: the louse Lemurpediculus verruculosus.

This louse is much like the ones you're familiar with. It clings to a host's hairs while sucking its blood, and is happy to switch hosts if another animal comes in close physical contact. The brown mouse lemur's louse lives mainly on the primate's ears, where fur is sparser and skin is easy to reach. It also hangs out on lemurs' eyelids and testes.

(I declined the authors' advice to "See Figure S1a for an image of the lice observed on the testes.")

Led by Sarah Zohdy from the University of Finland, researchers trekked into the jungle and placed traps for mouse lemurs, baiting them with fresh banana. During their study period, they managed to catch 32 of the elusive primates. On each lemur, the researchers did a thorough lice check with a comb, like a kindergarten teacher would. (They note that it's easy to spot the lice since their size is so great compared to the size of the lemur.) Then, without removing any lice, they marked the bugs on each lemur's ears with a lemur-specific code--a set of colored nail-polish dots applied to every louse's back with a toothpick--and after a few seconds for drying, set the lemurs free again.

Whenever the team recaptured a lemur they'd already seen, they checked the animal's lice to see whether it was still carrying only its own bugs, or had shared with a friend. Their observations coincided with the lemurs' brief breeding season, during which they expected to see a sharp increase in sharing.

Sure enough, almost all the louse swaps that Zohdy and her team observed happened during the breeding season. They also happened exclusively between males, who were the main carriers of lice. Among the 9 female lemurs they captured, the researchers found just 1 with lice. But 14 out of 23 males were infested at some point during the experiment.

Though male lemurs are known to share nests, Zohdy speculates that the spike in louse sharing during breeding season comes from males grappling with each other to compete for females. It's possible that some lice were transferred during mating, spending time on female lemurs in between male hosts. But for the most part, the lice seem to prefer male company.

And we're not just talking about their choice of host. Though the researchers only marked lice that were living on lemurs' ears, they usually found these same lice later living on a host's testes. The lice may prefer this piece of real estate because of its thin fur and rich blood supply--especially during the breeding period when these appendages are, in the authors' words, "dramatically distended." ("See Figure S6 for an example.")

The lice seemed to say, then, that male mouse lemurs have the closest contact with each other when they're fighting over females during mating season. They also revealed that brown mouse lemurs range farther than previously thought. Based on previous trapping studies, the researchers expected that lemurs would stay within a small range, and that louse sharing would decrease as they got farther from their home base. But lemurs surprised researchers by spreading their lice far afield.

So brown mouse lemurs aren't homebodies, after all. And though they're shy, they may bump elbows with plenty of their peers during mating season. This information isn't just useful for understanding the lives of lemurs: Since lice and other parasites can carry diseases, knowing how they travel can help scientists predict the spread of infections.

The technique of using parasites as surveillance bugs could help scientists spy on other hard-to-find animals and learn more about their lives--sordid details included.

Zohdy, S., Kemp, A., Durden, L., Wright, P., & Jernvall, J. (2012). Mapping the Social Network: Tracking lice in a wild primate (Microcebus rufus) population to infer social contacts and vector potential BMC Ecology, 12 (1) DOI: 10.1186/1472-6785-12-4

Images: Iraiidh/Wikimedia Commons; Sarah Zohdy.

How Stress Makes Oranges Better for You

Though Sicily may seem like a relaxing oasis, it's really a stressful climate where rogue elements can turn you bloody--whether you have a run-in with the mafia, or you're an orange. New research shows why the Italian blood orange prefers this hostile environment to your backyard. With a little coercion, though, we might someday convince this extra-healthy fruit to move abroad.

A variety of the sweet orange Citrus sinensis, the blood orange has eerie red flesh and is grown most successfully around Sicily. To develop their trademark color, the oranges need to ripen in a climate where the nights are much colder than the days. They're cultivated in a few other places outside of Italy, and their color can be enhanced by storing them in the cold after picking them. But in general, the blood orange is an inflexible character.

The blood orange's pickiness makes it hard to mass produce and get onto grocery store shelves. A team of researchers from the United Kingdom, Italy, and China (where another variety of blood orange grows) set out to find what makes the orange so finicky.

Pigments called anthocyanins give the fruit its gory look. These same pigments are responsible for the deep purplish hues of blueberries, eggplant peels, and Japanese maples. Combing through the blood orange's DNA, the researchers found a gene they named Ruby that turns on the fruit's anthocyanin machinery.

When Ruby is activated, the plant makes anthocyanin and the orange turns red. To demonstrate this, the researchers snuck the Ruby gene into a tobacco plant. Tobacco leaves normally make anthocyanin only in small amounts. But with Ruby added to their genes, tobacco plants cranked up the pigment's production and sprouted reddish leaves.

If Ruby is the foreman who hits the ON button at the anthocyanin factory, he apparently needs a cold snap to get him out of bed--because without cold nighttime temperatures, blood oranges don't turn bloody. The researchers discovered that the element waking Ruby up is a kind of rogue gene called a transposon.

Also called "jumping genes," transposons are chunks of DNA that can hop around a genome and insert themselves wherever they like. At some point in the blood orange's evolution, a tranposon stuck itself right in front of Ruby and became the on-switch for the on-switch.

Ordinarily, the plant suppresses the transposon. It's not a good idea, after all, to let wandering genes start bossing around the rest of your DNA. But transposons often get turned on when plants are stressed. Scientists think this may be a desperate trick plants evolved to use when times are tough: The normal order of business isn't working, so plants set their rogue genes free to see if they have any useful innovations. When blood orange trees are stressed by cold temperatures, they release their hold on the transposon in front of Ruby. The transposon wakes up the factory foreman, and you know the rest.

Now that we've found the secret to making blood oranges bloody, senior author Cathie Martin says genetic engineers could create a new variety that doesn't need the cold at all. Scientists could tweak the orange's genome so that Ruby is active all the time, keeping the pigment factory going in any temperature.

Imagining a job for a task force of tree psychologists, I asked Martin if we could grow unmodified blood orange trees in warm climates and just stress them out some other way. But she said that probably wouldn't work. You also can't create a blood orange by chilling regular "blonde" oranges or orange trees--this particular team of rogue gene and factory foreman is specific to this variety of Citrus sinensis.

Of course, you could always just stick to the fruits that grow easily in your climate. But Martin says blood oranges are even better for us than regular oranges. "There are many examples of...dietary anthocyanins having a beneficial effect on health," she says, "especially for cardiovascular disease and obesity." In mice, blood orange juice (but not regular orange juice) limits weight gain and prevents obesity.

If these pigments are as healthful as they seem--and especially if climate change is going to make the tree's home turf less comfortable--maybe it's worth pursuing a way to get the blood orange out of Sicily.

Butelli, E., Licciardello, C., Zhang, Y., Liu, J., Mackay, S., Bailey, P., Reforgiato-Recupero, G., & Martin, C. (2012). Retrotransposons Control Fruit-Specific, Cold-Dependent Accumulation of Anthocyanins in Blood Oranges THE PLANT CELL ONLINE DOI: 10.1105/tpc.111.095232

Image: ccharmon/Flickr

When Keen Minds Are Quick to Wander

We're all afflicted with wandering minds. Those that are especially prone to gallop away during an easy task may just have more horsepower to begin with.

Working memory is the place where your mind holds and manipulates the things you're currently thinking about. If you can fit more items in there at once, you have a better working memory capacity--and odds are you score better on IQ and other tests. Previous studies have shown that when our working memory is busier, our minds wander less. Does this mean wandering uses resources from working memory, taking valuable brainpower away from other tasks?

Daniel Levinson, a graduate student at the University of Wisconsin, Madison, led a study of working memory and mind wandering. Scientists call wandering "task-unrelated thought" or TUT, as in the chastising sound you might imagine when you catch yourself drifting away from your work.

Levinson used two experiments to study whether people with better working memories are more likely to let their attention drift during a simple assignment. In the first experiment, 74 subjects performed an easy visual task on a screen, pressing keys in response to the letters they saw. In the second, 42 subjects did an even duller task, pressing a key in time with their own breathing. Both experiments were periodically interrupted by a message on the computer screen asking whether subjects had just been thinking about something besides the job at hand.

All subjects also completed a standard test of their working memories. In both experiments, people with higher working memory scores reported more episodes of mind wandering (or TUT).

Levinson thinks that since the tasks used here were simple, using only a minimum of working memory resources, subjects' minds were free to wander. Those who had greater resources to begin with had more left over after clicking the keyboard, and tended to spend it elsewhere--say, planning a grocery list. In previous studies, more challenging tasks had eaten up working memory resources and left little behind for daydreaming.

Of course, a correlation between working memory and mind wandering doesn't prove that one causes the other, as Levinson readily agrees. To show that, he says, you'd have to increase individuals' working memory and see that their ability to mind wander also increased. Alternatively, maybe people with better working memories just find these computer-screen tasks easier to begin with, and that sends some other part of their minds meandering.

But Levinson says the subjects in his study with higher working memory, for the most part, didn't outperform others (as you might expect if they found those tasks easier). When researchers removed the one measure by which those subjects did do better from their analysis, the result stayed the same: Minds with greater working memory resources wandered more.

If mind wandering really does depend on working memory, Levinson says there are various theories about how that relationship might work. One idea is that a fragmentary thought can pop into your consciousness spontaneously, or because your stomach rumbles and reminds you of lunch. Your working memory may grasp that fragment and spin it into a longer yarn of thought: Where should I get lunch today? After lunch do I have time to go to the library? Now you're gathering and elaborating on bits of information that aren't in your immediate environment--a job that requires your working memory.

Levinson thinks this kind of research could lead to training methods that help people keep their minds on task. Until then, maybe we can hack the system on our own.

To keep my own mind on task while I'm writing, I like to be in a mildly distracting environment. A subdued Starbucks works, as does playing classical music at my desk. (TV, music with lyrics, or that horrible guy on his cell phone next to me at Starbucks do not work.) Paradoxically, giving myself a small distraction to handle seems to help me focus. Judging by the scarcity of open outlets at most coffee shops, I'm not the only person who does this.

I asked Levinson whether committing part of my working memory to tuning out a distraction should help tone down my mental chatter. "Yes!" he said. "People with more working memory are better at blocking out visual distractors on a screen. So people think that working memory is used to filter out distractions." Spending some resources on this task should leave me with less free rein to wander. Though, he points out, I'd also have fewer remaining resources for the task at hand.

Levinson suggests a different trick. Working memory is known for helping you keep track of your priorities and override your habits, he says. If you set a goal to rein in your mind when you notice it wandering, the simple act of remembering that goal may claim some of your working memory resources and make you less likely to drift.

Though this tactic may sound like a recipe for frustration (Wandering again? Tut tut!), Levinson considers it empowering. "It's a choice that I'm actually making when I elaborate on my mind wandering, and I'm using my resources when I do it," he says. "I also have a choice to invest those resources somewhere else."

There's also the zen approach. "It's impossible not to mind wander," Levinson says. "On average, people will mind wander for half of their daily lives." We can't help it. But maybe we can take a moment along the way to appreciate what a mobile mind says about our brainpower.

No, really, just a moment. You can go now.

Levinson, D., Smallwood, J., & Davidson, R. (2012). The Persistence of Thought: Evidence for a Role of Working Memory in the Maintenance of Task-Unrelated Thinking Psychological Science DOI: 10.1177/0956797611431465 

Image: VickyvS/Flickr

How to Slim Down, Manage Your Man, and Stay Tight with Your Girlfriends!

Who ever said science wasn't for us ladies? This week's research is full of tips on looking good, eating right, and taking care of your man! Plus: Don't miss a shocking true story about a girls' get-together turned deadly.

The calorie-free way to de-bland your diet
You try to eat right. But sometimes that low-sodium poached chicken breast on lettuce doesn't thrill your taste buds. What if merely looking at pictures of steak, pizza or pastries made your healthy meal taste heartier? New research from Switzerland says that just might work.

A group of Swiss scientists studied 14 healthy adults. The subjects held an electrode on their tongues while researchers flashed pictures of foods in front of them. The electrode gave off little buzzes of "electric taste," triggering subjects' taste buds with a neutral, slightly metallic taste.

People experienced a more pleasant flavor in their mouths when the electric taste was paired with a high-calorie food picture than a low-calorie one. The scientists say these images of forbidden foods light up the parts of our brains that go "Mmm!"

Could you try this trick in your own home? The researchers didn't study what happened when people ate actual food while looking at pictures. But if your gluten-free, high-fiber bread is blander than a piece of metal, staring at a picture of chocolate cake might make it seem tastier.

This surprising workout trick will have you handing back unwanted pounds!

If you're overweight, you might find exercise frustrating. Just a few minutes of exertion can leave you feeling overheated and sweaty. But research presented at an American Heart Association meeting may provide a solution to your problem: colder hands.

Researchers at Stanford University conducted a small study on obese women between the ages of 30 and 45. All the women participated in a 12-week exercise program that included push-ups, lunges, and using a treadmill. Half the women held their hands in cylinders of cold water while they were on the treadmill, while the other half kept their hands in body-temperature water.

Because the women who exercised with their hands in cold water stayed cool, they were less likely to get frustrated and drop out of the exercise program. (They even stuck it out through those dreaded push-ups!) These women lost more weight and got in better shape than the other group of women.

You probably don't have one of these cold-water exercise devices in your local gym. But you can still apply the findings to your own exercise routine. In the summer, why not freeze water bottles and hold them in your hands while you work out? And in colder months, get outside and ditch those gloves! After all, everyone can agree that a beach-ready body is worth a little numbness in the extremities.

Are cheeseburgers turning your guy's swimmers into toast?

Bad news, drive-through lovers! Fertility specialist Jill Attaman says a diet high in saturated fat is bad for sperm counts.

Attaman studied the swimmers of 99 men who came to a fertility clinic. She also gathered data about the men's diets and divided them into three groups based on their fat intake. The men in the highest fat-consuming group had sperm counts 43 percent lower than men who consumed the least fat. That's news that will chill some men's hearts colder than a Shamrock Shake.

But it's not all bad news for fats. While saturated fats were tied to low sperm counts, healthy fats called omega-3's seem to be good for sperm. Men who were in the highest third for consumption of this kind of fat had healthier, better-formed swimmers. So next time you cook your burger king a thoughtful dinner, think of his own little sesame seeds and try salmon instead of steak.

"I was part of a hot defensive bee ball"

Bertha,* a Japanese honeybee, was hard at work in her hive one day when she became aware of an intruder. A giant hornet, Vespa mandarinia japonica, was inside the entrance of the hive. Suddenly Bertha found herself swept up in a buzzing mass of bodies.

"I'd heard rumors about the hot defensive bee ball before," Bertha says, "but I'd never been a part of one myself." The sister honeybees clumped together in a tight swarm around the massive body of the hornet. (They don't call them giants for nothing. Check out some mug shots of these unpopular predators here.)

Vibrating their muscles to generate heat, the bees cranked the temperature in the swarm up to 46 degrees Celsius, or 115 degrees Fahrenheit. That's even hotter than your Bikram class! It was uncomfortable for Bertha--but for the hornet, it was worse.

Within an hour, the hornet was dead. The bees dispersed. And that's when they found themselves, instead of at the hive's entrance, inside a glass beaker. The attack had all been a ruse perpetrated by scientists. The hornet hadn't even been coming after the bees in earnest; researchers had shoved it inside the hive on a wire.

"I felt sort of used," Bertha says. "I was just swept up in the moment, and now I know I was manipulated into joining the bee ball. But at least it was for science." (Bertha was luckier than some of her sisters, who were forced to donate their heads to science as well.)

The researchers wanted to find out what genes were activated in bees' brains while they formed the hot defensive bee ball. They found one gene of note. But the same gene was active when bees were heated up outside of the bee ball. So it seems to be a response to the furnace-like environment the bees create, not a cause of the mysterious ball-forming impulse.

To find out what drives bees to form hot, deadly mobs in the first place, scientists--and Bertha--will have to wait.

*Some names have been changed.

Ohla, K., Toepel, U., le Coutre, J., & Hudry, J. (2012). Visual-Gustatory Interaction: Orbitofrontal and Insular Cortices Mediate the Effect of High-Calorie Visual Food Cues on Taste Pleasantness PLoS ONE, 7 (3) DOI: 10.1371/journal.pone.0032434 

Attaman, J., Toth, T., Furtado, J., Campos, H., Hauser, R., & Chavarro, J. (2012). Dietary fat and semen quality among men attending a fertility clinic Human Reproduction DOI: 10.1093/humrep/des065

Ugajin, A., Kiya, T., Kunieda, T., Ono, M., Yoshida, T., & Kubo, T. (2012). Detection of Neural Activity in the Brains of Japanese Honeybee Workers during the Formation of a “Hot Defensive Bee Ball” PLoS ONE, 7 (3) DOI: 10.1371/journal.pone.0032902 

Images: plates of food Ohla et al.; glove peanutian/Flickr; burger guy Mr. T. in DC/Flickr; bee klugi/Flickr

Accounting for Taste: Why a Bear, but Not a Seal, Will Steal Your Cupcake

Humans aren't the only mammals with a sweet tooth. Omnivores from beagles to grizzlies can detect a wide range of flavors and enjoy the taste of sugar. But other mammals with narrow carnivorous diets have been subjected to evolution's "use it or lose it" decree. These meat-eaters are genetic mutants without working taste receptors for sweets. Not only do they not want your cupcake, but they can't even taste it.

Researchers led by Peihua Jiang at Monell Chemical Senses Center in Philadelphia wanted to know how often evolution has removed tastes from animals' repertoires. Omnivores such as humans can detect five basic tastes: sweet, sour, bitter, salty, and umami (a meaty flavor). Previous studies had shown that cats, though, are indifferent to sweetness. Cats were also known to have a mutation in the gene for the sweet taste receptor, rendering it nonfunctional. Had other carnivores' sweet receptors met the same fate?

For 12 carnivore species, the authors sequenced the genome section containing the sweet taste receptor. In just 5 of these species, the gene was intact. These included the aardwolf, Canadian otter, spectacled bear, raccoon, and red wolf.

It was presumably not practical to round up all these animals and give them tests to confirm that they like sugar. But the authors were able to test four spectacled bears, a charismatic South American species. When given a choice between a bowl of plain water and a bowl of sugar water, the bears strongly preferred the sugar water. They even enjoyed some artificial sweeteners (Splenda, for instance, but not NutraSweet).

Spectacled bear: Yes cupcakes.

The other 7 carnivore species in the study had mutations in their sweet taste receptors. These animals came from widely separated branches of the mammal family tree: sea lion and seals; Asian small-clawed otter; hyena; fossa (a cat-like creature from Madagascar); and banded linsang (a secretive jungle creature from Southeast Asia).

Though, again, the authors didn't recruit any hyenas or jungle cats for their study, they did bring in two Asian small-clawed otters for testing. The otters were given the same bowls of sweetened and unsweetened water that the bears tasted. But the otters were totally indifferent to sugar water.

Asian small-clawed otter: No cupcakes.

An aardwolf, since you asked: Yes cupcakes, yes termites.

Finally, the researchers looked at the dolphin genome, which had been previously published. Not only was the dolphin's sweet taste receptor mutated, but so was the receptor for umami flavor. There seemed to be no intact gene for a bitterness receptor, either.

It seems incredible that an animal could be so deficient in tasting. But previous studies have suggested that dolphins can't taste sugar and have a reduced ability to taste bitterness. A close look at their tongues reveals only a few taste bud-like structures. The same is true of the sea lion: It has barely any taste buds, and has a mutated gene for the umami receptor as well as sweet.

They wouldn't have much chance to taste their food even if they did have taste buds, though, because neither sea lions nor dolphins chew their prey. They both gulp down fish whole.

Dolphin: No cupcakes, no chewing.

Despite these similarities, sea lions and dolphins lost their taste separately. Their lineages took to the sea separately and 15 million years apart. Their genetic mutations, too, are different.

In fact, out of all the genetic anomalies the researchers found in carnivores' sweet taste receptors, no two mutations were the same. This means that again and again, evolution has removed the ability to taste sugar from carnivores. There must be some cost, then, to keeping unnecessary taste receptors. When animals evolve to consume an all-meat diet, it's better for them to prune their unnecessary tastes. And when they evolve to swallow their food whole, it seems there's not much need to taste anything.

Even within close families of mammals, evolution has tweaked individual species' taste receptors as they evolved different diets. Black bears love raisins but also enjoy insects and fish; panda bears, which only eat bamboo, can't taste umami. Though many bats feed on fruit, the vampire bat only eats blood and can't taste sugar.

Taste receptors aren't purely for enjoyment, though. A bitter or sour taste can be our clue that a food is spoiled or toxic. So it's surprising that even the bitter taste receptor, which evolved for our protection, can apparently be thrown away. 

Maybe when animals have a strictly specialized diet (of fish, or bamboo, or blood) they can rely on their eyes and other senses to ensure they're eating the right thing. But we omnivores have to decide on our diets by taste. It means we must think harder about what we're eating--but it also means we can enjoy every flavor of cupcake.

Jiang, P., Josue, J., Li, X., Glaser, D., Li, W., Brand, J., Margolskee, R., Reed, D., & Beauchamp, G. (2012). Major taste loss in carnivorous mammals Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1118360109

Images: bear Cburnett/Wikimedia Commons; otter Patrick Gijsbers/Wikimedia Commons; aardwolf Dominik Käuferle/Wikimedia Commons; dolphin Just Taken Pics/Flickr.

Note: This post was originally titled "Accounting for Taste: Why a Bear, but Not an Otter, Will Steal Your Cupcake." But my attentive husband pointed out that there was a type of otter in the sugar-tasting group, as well as the sugar-ignoring one. I should admit now that I actually don't know whether any of these animals steals pastries.

This post was chosen as an Editor's Selection for

Bees and Humans Crave Novelty for the Same Reasons

You might not expect to find much in common between a human brain and the brain of a flying insect that’s happy to sacrifice itself, for its colony’s safety, by tearing off its entire back end in your arm. But certain bees share a personality trait with certain humans. Even if their needs are met at home, they’re compelled to go searching for new experiences. And shared brain chemistry might be what’s driving both of us.

Although the worker bees in a hive are closely related sisters, they can have different habits. Some tend to “scout,” an activity that comes in two flavors. Nest scouting happens when a swarm of bees defects from its home hive and goes in search of a new place to live; the scouts seek out good locations and then report back to the group. And food scouts go searching for new flower patches to feed from, even if the colony is already well fed. (Then they give other bees directions to the food source with a dramatic performance called a “waggle dance” that, incredibly, conveys location and distance.)

Researchers at the University of Illinois Urbana-Champaign and elsewhere did some personality testing on bees to find out how consistently scouts like to scout. Do the same bees always strike out on their own, or does everyone take shifts?

In tests on eight different colonies, the researchers found and marked the bees that worked as nest scouts or food scouts. They discovered that, while the overlap wasn't total, nest scouts were much more likely to be food scouts too. To find the bees that most liked to scout, the researchers trained a hive to eat at a feeder. Then they began placing new feeders farther away inside the bees' enclosure. The bees that were most likely to check out these alternate feeders, instead of staying at the close one, were collected and studied.

The tiny brains of the scout bees (as well as non-scouts) were cut up and examined to see which of their genes were working hardest. "Scouts and non-scouts show massive differences in brain gene activity," says senior author Gene Robinson. These differences appeared in the activity of genes controlling several brain chemicals such as glutamate and dopamine.

Was the scouts' altered brain chemistry the cause of their behavior, or a consequence of it? To find out, the team collected non-scouts and fed them sugar water laced with drugs. (Robinson says it's easy to convince honeybees to take their medicine. "Bees love sweets!")

When they ingested the brain chemical glutamate, non-scouts changed their behavior and became more likely to scout. But when they were fed with a molecule that blocks dopamine, the non-scouts were even less likely to scout than usual.

It's not clear how these neurochemicals interact to increase or decrease scouting behavior. But it seems that both glutamate and dopamine act in the bees' brains to influence their scouting personality.

Some humans, too, are more likely to go in search of new sensations. Psychologists call this behavior "novelty seeking." People who score high on this personality trait are more likely to abuse drugs. And like the bees, they display differences in how their brains handle dopamine. Novelty seeking in humans has also been linked to glutamate in the brain--again, like the bees.

It's highly unlikely that bees and humans inherited our shared brain chemistry from our distant common ancestor. (Robinson told ScienceNOW that this was "probably some kind of marine flatworm"--not an animal that would have expressed many personality traits at all.) Instead, we seem to have converged on the same behaviors, compelled by the similar actions of messenger chemicals in our brains.

Seeing our personalities reduced to the mindless actions of molecules moving through our brains can be unsettling--especially when we're being compared to insects. But it makes the lives of bees who travel far from the hive seem pretty close to home.

Liang, Z., Nguyen, T., Mattila, H., Rodriguez-Zas, S., Seeley, T., & Robinson, G. (2012). Molecular Determinants of Scouting Behavior in Honey Bees Science, 335 (6073), 1225-1228 DOI: 10.1126/science.1213962

Photo: Chiot's Run/Flickr

Penguins Recognize the Squawk of a Champion

It was the middle of the night when researchers snuck up to nesting penguins on the coast of New Zealand and stole the eggs out from under them. Placing the warm eggs in an incubator for safekeeping, they slid artificial eggs back under the penguins' bodies. Each replacement egg held a heart monitor that was now pressed against a parent penguin's skin. Then the researchers crept away and prepared to give the penguins a bit of a scare.

Little blue penguins (also called fairy penguins, or simply little penguins) are the world's smallest and bluest penguins. They live in burrows on the southern coasts of Australia and New Zealand. During the breeding season, males and females pair off and share the responsibility of keeping their eggs warm.

These penguins are both territorial and chatty. They "bray" to announce themselves, and seem to recognize other individuals' calls. If a territorial dispute between two little blue penguins comes to a scuffle, the winner gives a final bray of victory at the fight's conclusion.

Researchers in New Zealand wanted to know if these announcements of victory--called "triumph displays"--are followed by local penguins like the nightly news. Do penguins inside their burrows eavesdrop on tiffs going on around them, listen for the voice of the winner, and then make sure to give that champion penguin a little extra room?

Led by Solveig Mouterde at the University of Waikata, a group of researchers carried out the stealthy egg swaps described above. They conducted their experiment at night, when the birds are active on land; each nest was occupied by either a lone male or lone female penguin who was tending the eggs while his or her partner fished at sea. After sneaking away and giving the penguins some time to settle down with their new, electronic offspring, the researchers began broadcasting the sound of penguin brays from speakers.

They used recordings taken from a distant colony of penguins, so the individuals in this study wouldn't recognize any voices. Each penguin heard a short soap opera of penguin calls: First, an exchange of territorial squawks between two male penguin voices. Then, the sounds of a scuffle ("i.e. flipper slapping"). After the fight, a final bray of victory from one of the two penguins. Finally, five minutes later, the distinctive squawk of either the winner or loser penguin--but now right outside the listening penguin's burrow, as if approaching.

Once the researchers swapped the heart-monitor eggs back out for the penguins' real eggs, they studied their recordings to see how penguins reacted to the nighttime drama.

They saw that female nest-sitters had elevated heart rates when either of the recorded penguins "approached" their burrows. Males' responses, though, depended on whose voice it was. If the approaching voice matched that of the winner in the mock fight they'd just overheard, male penguins kept quiet and their heart rates became elevated. But if they heard the voice of the loser, male penguins stayed calm. They were also more likely to squawk right back at the potential intruder, as if to say, "Back off, I know you're not so tough!"

It seems that little blue penguins can not only recognize other individuals' voices, but eavesdrop intelligently on the interactions happening outside their burrows.

After two penguins have tussled over territory, it benefits the winner to give a victorious squawk: He lets other penguins know that they shouldn't mess with him, and saves himself the effort of having to fight another day. It also benefits nosy neighbor penguins to listen in on a scuffle. By paying attention to who wins and loses fights, they can avoid the king of the ring and save themselves from an embarrassing trouncing.

These ten-inch-tall penguins can follow their neighborhood social dynamics just like an eavesdropping human would. That's not bad for a bird that can't even tell when it's babysitting a piece of plastic.

Mouterde, S., Duganzich, D., Molles, L., Helps, S., Helps, F., & Waas, J. (2012). Triumph displays inform eavesdropping little blue penguins of new dominance asymmetries Animal Behaviour, 83 (3), 605-611 DOI: 10.1016/j.anbehav.2011.11.032

Image: Tanya Dropbear/Wikimedia Commons

Your Sense of Sight Helps You Smell

Imagine the smell of an orange. Have you got it? Are you also picturing the orange, even though I didn't ask you to? Try fish. Or mown grass. You'll find it's difficult to bring a scent to mind without also calling up an image. It's no coincidence, scientists say: Your brain's visual processing center is doing double duty in the smell department.

Since previous studies had shown that the brain's visual center lights up with activity when someone does a purely smell-related task, a group of researchers set out to test what these two senses have to do with each other. Does the smell merely remind us of the visual? Or do our brains actively route scent input through the visual cortex, because it's a crucial step in our processing?

Led by Jahan B. Jadauji at McGill University, the researchers tested this using a potentially alarming tool called repetitive transcranial magnetic stimulation (rTMS). The technique involves a large coil, placed against a person's head, that sends magnetic pulses into a chosen region of the brain. The electric current startles that area of the brain into extra activity. TMS coils are sometimes aimed at the front left of patients' brains to treat major depression.

Here, researchers placed the TMS coil at the back and base of the skull, where the brain's visual processing center (counterintuitively enough) sits. Magnetic pulses stimulated the visual cortex, an effect that would linger throughout the testing session. Researchers first made sure of this by testing their subjects' visual perception and observing that it improved after TMS.

Both before and after their visual centers had been excited by magnetic stimulation, subjects sat for a smelling exam. They first sniffed scent-holding pens of different strengths to measure their noses' sensitivity. After TMS, subjects sniffed sets of three identical-smelling pens and told researchers which was the strongest. Then they sniffed sets of three equally intense pens and decided which of the three had a different smell (cloves? lemon? turpentine?) than the other two.

Finding the strongest smell didn't require subjects to identify what the smell actually was--and they didn't do any better on this task after their visual cortices were amped up with TMS. But finding the mismatched smell out of a group made subjects think a little harder about what they were smelling. And on this task, subjects performed better after TMS.

The researchers also tried a sham TMS procedure, in which coils were held to subjects' heads but didn't actually fiddle with their brains. And they tried aiming the magnetic stimulation at subject's hearing centers, rather than visual. Neither of these steps improved subjects' performance at picking out mismatched scents. Only stimulating the visual cortex did the trick.

This means, according to Jadauji, that the brain's visual processing center is specifically involved in how we process smells. Marring the curriculum plans of kindergarten teachers everywhere, our sense of smell--or at least our skill at identifying different smells--may rely on our sense of vision.

It's intriguing to wonder what other parts of our brains might be secretly conspiring in this way. Do we also use our visual centers when we identify sounds? Or touches? If identifying a smell requires that we call up a mental image, do we also carry that processing a step further into our language centers, naming the thing we've identified? A previous study found a connection between mental illness and the ability to identify smells. Tracing the connections between our senses might lead to a better understanding of functional and dysfunctional brains.

Of course, it's hardly news that people's senses can play together in unexpected ways. Earlier, I was tempted to write that it's "impossible" to imagine a scent without an image, but I remembered that I kind of have a problem keeping my senses separated. Don't feel too superior. It may turn out that everyone is a little bit synesthetic after all.

Jadauji, J., Djordjevic, J., Lundstrom, J., & Pack, C. (2012). Modulation of Olfactory Perception by Visual Cortex Stimulation Journal of Neuroscience, 32 (9), 3095-3100 DOI: 10.1523/JNEUROSCI.6022-11.2012

Photo: by Jippolito/Flickr

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