Gibbon Moms Help Daughters Practice Their Singing for Future Mates

Before their daughters grow up and leave home, mothers may impart some lessons in the womanly arts—for example, the proper way to whoop and hoot with your mate while sitting in a tree branch. As an adult, a female gibbon sings elaborate duets with her male partner. But before she leaves the family, her mother seems to take responsibility for the daughter's vocal lessons.

Young gibbons spend many years learning to vocalize like adults. By age six or so, "sub-adult" apes can match the vocal prowess of a grownup. Mothers and daughters often sing at the same time, though it's not clear why. Researchers traveled into the rainforests of Sumatra to make audio recordings of gibbon families and try to figure out whether these sing-alongs are significant.

Lead author Hiroki Koda of Kyoto University and his colleagues studied six families of agile gibbons (that's a species name, not just a descriptor). Koda explains that gibbons are monogamous, and male and female young grow up with their parents before departing the group to find their own partners. Each family in the study included a nearly adult daughter, and the researchers captured recordings of these daughters and their mothers singing together.

They found that some daughter gibbons were better than others at singing in sync with their mothers. They were also better at matching their mothers' tunes. But these talented daughters actually duetted with their mothers less often. Koda thinks that's because the ones who "showed more skillful songs" are the most mature, and are nearly ready to leave home. Daughters who still need the practice sing with their mothers more often.

Here, a mother and daughter gibbon match each other's calls as they sing together:

The researchers also found that mothers who sing more often with their daughters—the ones who are still giving lessons—modify their own songs more when they do so. Koda says this may be similar to the "motherese" that humans speak to their babies. Like human moms talking slowly and at a high pitch, gibbon moms alter their vocalizations when duetting with their daughters.

Koda says that in the past, primate calls have been seen as "completely different from human language development." Rather than learning from their parents, young monkeys and apes seem to figure out their calls on their own. But this is the first evidence of mothers helping offspring learn to vocalize in gibbons—or any other nonhuman primate.

By paying more attention to vocal interactions between parents and offspring, Koda thinks scientists might discover other examples of primate parents getting involved in their children's learning. (After that, maybe they'll discover primate parents getting too involved. "Don't you take that tone with me, young lady! I heard what you just hooted!")

Images: Top, singing gibbon by patries71, via Flickr (not, as far as I know, the study species). Bottom, a mother gibbon from the study by Hiroki Koda.

Hiroki Koda, Alban Lemasson, Chisako Oyakawa, Rizaldi, Joko Pamungkas, & Nobuo Masataka (2013). Possible Role of Mother-Daughter Vocal Interactions on the Development of Species-Specific Song in Gibbons PLOS ONE DOI: 10.1371/journal.pone.0071432

The Hazards of Being an Athletic Ape

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


Image credit: Cpl. Michelle M. Dickson

Inner Ears Reveal Speed of Early Primates

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

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

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

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

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

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

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

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

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

This piece was first published on June 22 at ScienceNOW.


Image: Timothy Ryan/Pennsylvania State University

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

Having a Water Bottle for a Mom Not Ideal

In the wild, young rhesus macaques can reasonably expect not to have their mothers replaced by kitchen props. The monkeys depend on their moms to nurse them and tote them through tree branches while they're small, just like other primates. But a laboratory experiment in Maryland took these babies from their mothers and had them raised alone or in groups of their peers. The monkeys' strange infancies had physical and mental effects that lasted into adulthood.

At the National Institute of Child Health and Human Development (part of the National Institutes of Health), rhesus macaques born between 2002 and 2007 were randomly assigned to one of three groups. The lucky first group got to stay with their mothers, who kept their young close by while living in a large cage with other monkeys.

The rest of the young monkeys were taken from their mothers and reared by humans in a nursery for their first five weeks of life. Then, if they were in the second experimental group, they were put into a cage with three other monkeys of the same age. The four peers were left to "raise" each other, Lord of the Flies style.

The final group of monkeys, after being nursed by humans for five weeks, spent two hours a day in these same peer cages. During the remaining 22 hours, they lived alone in a cage with a "surrogate mother." The name is a bit of an insult to primate intelligence, though, since researchers describe this object as "effectively a terry cloth-covered hot water bottle hanging from the top of the cage."

By the end of their first year of life, all the juvenile monkeys had been moved from their experimental cages into one social group. Now the researchers, led by Gabriella Conti at the University of Chicago, began to collect data on the monkeys' health. Over the years of the study, they watched 231 rhesus macaques grow up in this bizarre daycare system. Even though the monkeys all ended up living together, their disparate childhoods left a mark.

The first clear effect was illness. Male monkeys that had been raised by a "surrogate" got sick nearly twice as often as mother-raised or peer-raised monkeys, even though by this time in their lives they all shared the same living conditions. Nearly every surrogate-raised male monkey had an illness at some point during the study.

Female monkeys that had been raised by peers, rather than by a real or fake mother, were more likely to have wounds and bald patches once they were living in the large group. Since these females displayed more aggressive behavior, the researchers think they may have been starting fights with the other monkeys. Their aggression may have goaded other monkeys into biting them and pulling their hair out.

And across all the groups taken away from their mothers—male and female, peer-raised and surrogate-raised—monkeys were more likely to have repetitive habits called stereotypies. In the zoo, a stereotypy such as pacing or swimming in circles suggests that an animal is in distress. In humans, stereotypies can be a symptom of autism. Habits displayed by the rhesus monkeys in this study included "digit sucking (the most frequent behavior), pacing, head tossing, self-grasping, saluting, spinning, rocking, circling, and swinging."

Some of the difference between monkeys raised by their mothers and the rest could be due to breastfeeding, Conti points out. But the increased illness in male monkeys was limited to the surrogate-mom group; the peer-raised monkeys, despite also missing out on breastfeeding, didn't have extra illnesses. And although all motherless monkey groups showed an increase in stereotypy, the effect was greatest in surrogate-raised males. This suggests that even if formula feeding causes some of the health effects seen here, it can't account for all of them.

The not-shocking conclusion is that monkeys need their moms to develop normally. Being raised parentless seems to make them less able to cope with infections or social stressors later in life. It's something to consider for research centers or zoos raising animals without their mothers. Even if the young have been orphaned or abandoned, there may be ways for human keepers to mitigate the damage.

Conti is an economist, though, and she's more interested in another primate: humans. She compares the rhesus research to studies of human children raised without either of their parents. These studies have found mental and physical health effects in children in Romanian orphanages, for example, or Israeli kibbutzim (where kids were raised communally). As smart and independent as we are, we're still primates who need someone to haul us through the tree branches when we're young.


Gabriella Conti, Christopher Hansman, James J. Heckman, Matthew F. X. Novak, Angela Ruggiero, & Stephen J. Suomi (2012). Primate evidence on the late health effects of early-life adversity PNAS : 10.1073/pnas.1205340109


Image: Baby Japanese macaque by Nemo's great uncle/Flickr

Dogs Understand Us Better than Our Closest Relatives

Does your dog understand you when you point at something? If so, this may be one of the few pop intelligence quizzes on which it can outscore a chimpanzee.

Previous studies had shown that dogs can pass a test in which a human points to a container and the dog must look inside it to find food. Human one-year-olds can pass this kind of test too. But chimpanzees have a hard time with it. Researchers at the Max Planck Institute for Evolutionary Anthropology in Germany wondered if these previous tests were unfair to chimpanzees. Would changing the setup of the experiment prove that chimps really do understand our gesturing?

In previous versions of the experiment, chimpanzees had been seated behind a barrier, while dogs were in the same room as the humans. Additionally, the objects that the animals were asked to choose between usually sat between the human experimenter and the chimpanzee--so the human didn't actually need the chimps' help to lift a container and get the food underneath. Perhaps the chimpanzees understood just fine when the human experimenter pointed to a cup, but thought, "Get it yourself, big-brain."

So the German researchers leveled the playing field between the two non-human species. They added a barrier between human and dog to make their setup more like the chimps'. They put the objects they were pointing to on the far side of their animal subjects, so the humans really couldn't reach the objects themselves. They also replaced containers and hidden food with boring, inedible objects, such as a rope or a sponge. Then they gathered 32 dogs and 20 chimps. ("For practical reasons," the authors write, "the studies of the chimpanzees and the dogs were conducted separately.")

First came a warm-up phase in which the experimenter encouraged the animal to fetch a single object (in exchange for a treat) by saying "Give it to me!" This taught the animals to associate the voice command with retrieving an object. But the experimenter didn't point or look at the object she wanted.

For the experiment itself, there were two objects in the room instead of one. The experimenter pointed to the one she wanted and repeated the "Give it to me!" command, moving her eyes between the animal and the desired object to make her point clearer. The dog or chimp had to turn around, retrieve the correct object, and bring it back to the experimenter to get a treat.

The chimpanzees flunked the test. While they consistently picked up one of the two objects and brought it back to the researcher, they only picked the correct object half the time. But the dogs, as a group, performed significantly better than if they were guessing. (And they did even better when the barrier between them and the human experimenter was removed.)

It's not that chimpanzees don't follow other animals' gazes. Previous studies found that great apes will look where a human is looking to check for anything of interest. But they don't seem to understand that gaze as a form of communication. And pointing with a finger--which is really just an exaggerated way to show where you're looking--doesn't help them.

Dogs, on the other hand, have evolved to be highly attuned to what humans want. As long as they pee outside and perform the duties we assign them (sheep herding, duck retrieving, company keeping) we give them food and warm place to stay.

Of course, dogs' understanding of human gestures will depend somewhat on their personal experiences with their owners. In this study, many of the individual dogs did not perform any better than chance. But earlier studies have shown that young puppies can understand human finger-pointing, while young wolves don't understand it as well.

The fact that chimps don't understand pointing as a form of communication suggests this isn't a universal ape gesture. They can follow a gaze and understand that other individuals have different perspectives; and the captive chimps in this study should have been especially used to communicating with people. But, fittingly enough, the gesture that says "go and fetch that thing for me" seems to be specifically human.


Kirchhofer, K., Zimmermann, F., Kaminski, J., & Tomasello, M. (2012). Dogs (Canis familiaris), but Not Chimpanzees (Pan troglodytes), Understand Imperative Pointing PLoS ONE, 7 (2) DOI: 10.1371/journal.pone.0030913


Photo: by me.

Chimps Prefer the 2-Point Conversion

If non-human great apes were coaching more football games, you could expect to see fewer extra points being kicked. We risk-averse humans usually prefer kicking an easy extra point after a touchdown, rather than attempting a more difficult 2-point conversion. But chimps and other great apes, after considering their odds, usually opt for the greater risk and the bigger reward.

By "reward," I mean banana.

Researchers at the Max Planck Institute in Germany tested a group of chimpanzees, bonobos, gorillas and orangutans on their risk-taking strategies using chunks of banana. They wanted to know whether the apes' likelihood to go hunting for banana pieces hidden under cups, rather than taking a smaller banana piece already in front of them, depended on the "expected value" of their choices. Expected value is simply an item's worth, multiplied by your odds of getting it. If a 2-point conversion attempt is successful exactly half the time, then its expected value is 1 point.

The 22 apes each sat through a series of experiments involving banana bits in cups. On one side of a table, they saw a small piece of banana placed under a yellow cup. Next to that was a row of blue cups,  anywhere from one to four of them. Under one of the blue cups was a larger piece of banana.

The apes knew the larger piece of banana was hidden under one of the blue cups, but unless there was only one blue cup, they didn't know exactly where the banana was. (They understood the setup because there was also a series of trials in which the apes watched the banana being placed under one of the blue cups.) In each trial, an ape could point to just one cup and get the reward--if there was any--underneath.

The yellow cup was a guaranteed small reward. The blue cups were a gamble. And the size of the gamble (in other words, its expected value) depended on how many blue cups were on the table. It also depended on the difference in size between the two banana chunks. The "safe" piece of banana in the yellow cup ranged from one-sixth to two-thirds the size of the large piece.

The researchers found that the apes' decisions did correlate to the expected value of their options. Overall, as the expected value of picking a blue cup increased--there were fewer blue cups on the table, or the safe piece of banana was small and untempting--apes opted more often to try a blue cup. When the expected value of the gamble was lower--because there were a lot of blue cups to choose between, or the safe banana piece was large to begin with--they were more likely to stick with the yellow cup.

Adjusting choices based on the expected value of each option is similar to how humans would decide. But the apes were less human-like in their general propensity for risk. Even at the lowest possible expected values, apes chose to gamble on a blue cup more than 50% of the time.

In other words, apes acted more like humans playing the lottery than humans kicking an extra point after a touchdown. These apes, of course, didn't have their coaching jobs on the line. They might have just enjoyed playing the cup game. And in a human football game, there are plenty of situations in which a kicked extra point is better than going for 2--even though its expected value, with a success rate of about 50%, is the same.

But even outside of football games, humans are known by psychologists for being risk averse, especially when it comes to potential gains. We'd rather take a small guaranteed reward than a larger and riskier one. (For losses, though, we tend to feel the opposite way.)

When the researchers broke down their results by species, they found that while all four species were risk prone, bonobos were a little more conservative in their choices than chimps were. With only a small number of ape subjects, it's hard to draw any serious conclusions. But it's interesting to speculate about the differences between us and our two closest living relatives. Have chimps evolved to take more risks, always gambling on finding something better, because in the wild they must search for fresh fruit year-round? Can bonobos afford to be more conservative because their diet in the wild is more flexible? What factor in our past put risk-averse humans at an evolutionary advantage?

Next time your favorite football team takes an overly conservative extra point, don't blame the coach for his evolutionary history. You could always call up the owners, though, and suggest they hire a chimpanzee instead.









Photo: Flickr/Mat_the_W 


Haun, D., Nawroth, C., & Call, J. (2011). Great Apes' Risk-Taking Strategies in a Decision Making Task PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028801

Are You Yawning Because Your Brain's Hot?

Everyone knows yawning is the pinkeye of social cues: powerfully contagious and not that attractive. Yet scientists aren't sure what the point of it is. Is yawning a form of communication that evolved to send some message to our companions? Or is the basis of yawning physiological, and its social contagiousness unrelated? A new paper suggests that yawning--even when triggered by seeing another person yawn--is meant to cool down overheated brains.

We're not the only species that feels compelled to yawn when we see others doing it. Other primates, and possibly dogs, have been observed catching a case of the yawns. But Princeton researcher Andrew Gallup thinks the root cause of yawning is in the body, not the mind. After all, we yawn when we're alone, not just when we're with other people.

Previously, Gallup worked on a study that involved sticking tiny thermometers into the brains of rats and waiting for them to yawn. The researchers observed that yawning and stretching came after a rapid temperature rise in the frontal cortex. After the yawn and the stretch, rats' brain temperatures dropped back to normal. The authors speculated that yawning cools the blood off (by taking in a large amount of air from outside the body) and increases blood flow, thereby bringing cooler blood to the brain.

If yawning's function is to cool the brain, Gallup reasoned, then people should yawn less often when they're in a hot environment. If the air outside you is the same temperature as your body, it won't make you less hot.

To test that theory, researchers went out into the field--namely, the sidewalks of Tuscon, Arizona--in both the winter and the summer. They recruited subjects walking down the street (80 people in each season) and asked them to look at pictures of people yawning. Then the subjects answered questions about whether they yawned while looking at the pictures, how much sleep they'd gotten the night before, and how long they'd been outside.

The researchers found that the main variable affecting whether people yawned was the season. It's worth noting that "winter" in Tuscon was a balmy 22 degrees Celsius (71 degrees Fahrenheit), while summer was right around body temperature. In the summer, 24% of subjects reported yawning while they looked at the pictures. In the winter, that number went up to 45%.

Additionally, the longer people had been outside in the summer heat, the less likely they were to yawn. But in the winter, the opposite was true: People were more likely to yawn after spending more time outside. Gallup speculates that because the testing took place in direct sunlight, subjects' bodies were heating up, even though the air around them remained cooler. So a yawn became more refreshing to the brain the longer subjects stood outside in the winter, but only got less refreshing as they sweltered in the summer.

The study used contagious yawning rather than spontaneous yawning, presumably because it's easier to hand subjects pictures of yawning people than to aggressively bore them. Gallup notes that contagious and spontaneous yawning are physically identical ("a stretching of the jaw and a deep inhalation of air," if you were wondering), so one can stand in for the other. Still, it would be informative to study people in a more controlled setting--in a lab rather than on the street, and preferably not aware that they're part of a yawning study.

A lab experiment would also allow researchers to directly observe whether their subjects yawned, rather than just asking them. In the field, researchers walked away while subjects were looking at the pictures, since people who know they're being watched are less likely to yawn. But self-reported results might not be accurate. The paper points out that "four participants in the winter condition did not report yawning during the experiment but yawned while handing in the survey to the experimenter."

Still, it seems there's real connection between brain temperature and yawning. It will take more research (and more helplessly yawning subjects) to elucidate exactly what the connection is. Even if brain temperatures always rise right before a yawn and fall afterward, cooling the brain might not be the point of the yawn--another factor could be causing the impulse to yawn, and the temperature changes could be a side effect. Studying subjects in a truly cold environment, and showing that they are once again less likely to yawn (because outside air would cool their brains too much), would provide another piece of evidence that temperature triggers the yawn in the first place.

None of this tells us why yawning is so catching, though. Personally, I think I yawned at least a thousand times while reading and writing about this paper. Maybe I should have taken some advice from an older study by Andrew Gallup, which found that you can inhibit yawning by breathing through your nose or putting something chilly on your forehead.

Photo: Wikipedia/National Media Museum

Andrew C. Gallup, & Omar Tonsi Eldakar (2011). Contagious yawning and seasonal climate variation. Frontiers in Evolutionary Neuroscience

Is the Aging Brain Uniquely Human?

Even if you stay free of Alzheimer's disease, the normal aging process is fairly destructive to your brain. Neurons disappear, connections lose their strength, protein gunk builds up, and the whole brain shrinks. Areas controlling learning and memory are among the hardest hit. A new study claims that our crumbling brains aren't just a fact of normal aging. Instead, they may be unique in the animal kingdom, the result of an evolutionary bargain our species has struck.

Chet Sherwood at George Washington University led the study, which put humans and captive chimpanzees of various ages through MRI scanners. The humans ranged from ages 22 to 88. Chimps were between 10 and 45 years old, because 45 years is about as long as chimps can live in the wild (more on that in a moment).

In humans, the researchers found a pattern of decreasing brain volume throughout life that accelerated into old age. That pattern was missing in chimpanzees, whose brains seemed to maintain a consistent size.

Chimpanzees were used because they're our closest living relatives; we've been apart for only about 6 million years of evolution. The authors reason that because chimps' brains don't shrink as they age, our own brain degeneration must be a product of our recent evolution. We've developed brains that are big and energy-hungry, and to judge from our global population size, throwing our resources into our noggins seems to have been a good evolutionary strategy.

Since splitting from our ape relatives, we've also evolved longer life spans. Women, in particular, are a curiosity because they can live decades past their fertile years. Evolutionary biologists have hypothesized that keeping infertile elderly women around is no accident, because these grandmothers can bolster the success of their own genes by helping to take care of their grandchildren. The authors of the chimp study suggest that these helpful grandmothers are to blame for our degenerating brains: we've evolved long lifespans and brains that can't quite keep up.

The grandmother hypothesis, though, is hard to prove. And though 45 is elderly for a chimpanzee in the wild, the authors acknowledge that chimps under medical care in captivity can live into their 60s. Is a human today who lives into her 80s, thanks to medical care and disease prevention, comparable to a chimp in the wild? Or is a human "in the wild" better represented by someone in a southern African country with a life expectancy in the 30s or 40s?

If this study included chimpanzees at the true upper end of their age potential, it might provide more insight. The authors acknowledge that some previous studies have shown different results; for example, a study of brain mass that included chimpanzees up to age 59 did find some shrinkage with age.

The authors assume our damaging brain decline is a byproduct of evolution, but don't ask whether it might come from extending our life spans even further than evolution intended. Some perspective might come from studying another animal that no longer lives "in the wild": domestic dogs. Wolves live six to eight years in the wild, but many kinds of pet dogs can live for twice that long.

Even though they're not close to us in evolutionary terms, dogs age much like humans do. Their brains shrink in old age, especially in the prefrontal cortex and the hippocampus--the same areas that are particularly vulnerable in humans. Dogs develop cognitive problems and behavioral changes. Their brains even accumulate deposits of amyloid-beta, the protein gunk that appears in humans and is linked to Alzheimer's disease. Maybe our aging brains are not only the result of our exceptional smarts, then, but also of our domestication.


Sherwood, C., Gordon, A., Allen, J., Phillips, K., Erwin, J., Hof, P., & Hopkins, W. (2011). Aging of the cerebral cortex differs between humans and chimpanzees Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1016709108

To Live Longer, Be a Happy Ape

Orangutans that achieve their goals, enjoy swinging with others, and always look on the bright side of the banana have longer lifespans than those who merely mope around the zoo. That's the conclusion of a long-term study of over 180 captive orangutans. The unhappy apes died sooner, and the happy apes lived to gloat about it.

Alexander Weiss at the University of Edinburgh and his colleagues collected data on captive orangutans in parks around the world. At the beginning of the study period, employees at each zoo who were familiar with the orangutans there rated the apes on their apparent happiness. Questions included how often each orangutan seemed to be in a positive or negative mood, whether it enjoyed social interactions, how well it was able to achieve its goals, and "how happy [raters] would be if they were the orangutan for a short period of time."

Over the next seven years, the researchers kept track of which orangutans had died. Though orangutans in captivity rarely live past their 30s, their aging process is similar to humans'.  And, as in humans, females tend to outlive males.

So it wasn't surprising that more male orangutans died during the course of the study. But the researchers also found that orangutans rated as happier at the beginning of the study were less likely to die over the seven years that followed.

One standard deviation in happiness, they found, was worth about five and a half added years of life. That means the difference between a pretty happy orangutan and a pretty unhappy orangutan is 11 years of living--no small change when you can only hope for 30 to 35 years to begin with.

What could cause unhappy apes to die younger? One possibility is that apes appearing less happy are already ill in some subtle, pre-symptomatic way. Another explanation is that a positive attitude evolved through sexual selection, like a set of showy tail feathers, as a signal to potential mates that Suzy or Sammy Sunshine has good genes. (Though being able to live into old age presumably isn't as important to potential mates as just living long enough to make some baby apes.)

A third possibility is that unhappy orangutans are experiencing more stress in their life, or have a poor ability to handle stress. Our bodies react to stressors by activating a hormonal system that gears us up to fight or flee whatever real or figurative predator is chasing us. It's a survival mode in the short term, but keeping that mode switched on in the long term is damaging to our bodies. Unhappy apes may have their lives shortened by stress.

The authors note that in orangutans, as in humans, happiness doesn't rely on outside circumstances. Part of it is inherited: you're born with your personality. But genes aren't fate, and aiming for a positive attitude--or the fruit on the high branch--might keep you swinging around the jungle into old age.

Image: harrymoon/Flickr

Weiss, A., Adams, M., & King, J. (2011). Happy orang-utans live longer lives Biology Letters DOI: 10.1098/rsbl.2011.0543

Our Killing Cousins

If you're feeling any guilt about belonging to the one species that encroaches on other animals' habitats, hunts them for sport, and drives them to extinction, consider this: we're not alone. There's another species capable of hunting its neighbor to near annihilation. Of course, it's our closest relative.

Chimpanzees eat mostly fruit and other plant matter. They were believed to be complete vegetarians until Jane Goodall first witnessed a chimpanzee hunt in the 1960s. An organized hunting party may chase a young monkey through the treetops, some chimpanzees blocking its escape routes while others wait in ambush. Meat is not only a nutritional resource for a chimpanzee community, but a social and political tool.

One of chimps' favorite animals to prey on is the red colobus monkey. And a new paper says that in Uganda's Kibale National Park, chimps are taking more than their fair share of monkeys. The red colobus population has declined sharply over the past few decades, and if they don't rebound soon, they could be wiped out entirely.

Previous studies had suggested that the red colobus monkey population in the park was declining, and that chimps might be to blame. So an international group of researchers set out to settle the question. They gathered data in the park for nine years, then added it to data from several previous studies to produce almost 33 years' worth of observations.

Rather than trying to find and count every primate in the forest, researchers took a kind of cross-section by walking along a predetermined route and recording what monkeys and apes they crossed paths with.

What they found was quite pronounced: between 1975 and 2007, the population of red colobus monkeys decreased by 89%. Their decline was tied to a significant, though less dramatic, increase in the chimpanzee population. The researchers ruled out various other explanations for the apparent red colobus loss, including disease, lack of food, shyness around strolling scientists, and being eaten by eagles. Habitat loss and poaching, the usual human-based causes of species loss, were ruled out by the national park's protections. The chimpanzees, with their suspiciously expanding population, were the only remaining culprits.

This is the first time scientists have observed one species eating another species into a serious population slump. Usually, non-human species are forced to maintain a balance with one another. But the chimps at Kibale are managing an eerily human overuse of resources.

Of further concern is the fact that both species are already endangered, thanks to humans. The red colobus population might not be so fragile if we hadn't driven its numbers down to begin with. Or perhaps overhunting is a new chimpanzee behavior, an adaptation that would have appeared without our interference. Either way, now that one endangered species is threatening the survival of another, can conservationists afford to stay out of the animals' business?

The authors of the study think there's hope for the red colobus in Uganda, because their population's plummeting seemed to slow or stop near the end of the study period. Observations by other scientists suggest that the monkeys in the park have dramatically expanded their ranges since the 1970s; that is, individual monkeys seem to roam over a much wider area of land than they used to. This may be their attempt to avoid hunting chimpanzees. If it works, the monkeys will have saved their species from not one, but two primate threats.


Images: Thomas Lersch/Wikimedia Commons, Olivier Lejade/Wikimedia Commons

Botswanavision

Do you ever find yourself squinting into the glare of your computer screen around 4 PM and thinking that your eyes aren't built for this? You're right, of course. The human eye evolved on the African savanna. This is what it's built to see:

Scientists from the University of Pennsylvania and elsewhere took about 5,000 digital photos in a Botswana savanna. They captured natural scenes at various times of day, from sun-baked vistas to up-close tree bark to fresh elephant dung, and compiled the images into a publicly available database.

Clicking through the albums may make you feel overheated, but it also simulates a pleasant stroll through the savanna. (Spoiler alert: baby baboons!)

The researchers used this database to investigate the evolution of the human eye. Specifically, they wanted to find the logic behind how our color-sensing machinery is set up.

Our eyes detect color using cone cells, which come in three types: one that detects light at short wavelengths (blue), one for medium wavelengths (green), and one for longer wavelengths (red). The three types of cones aren't distributed evenly across the retina, though. The blue-detecting cones are rare, and mostly exist around the outer edges of the retina. The red and green cones are much more common, but the ratio between them varies widely from person to person.

For each of the scenes in the Botswana photo database, scientists calculated how much light of different wavelengths would be reaching the viewer's eye. Based on those numbers, they mathematically determined the most efficient distribution of cone cells in the retina. They found that blue-detecting cones couldn't pick up as much information as the red or green cones (which explains why we don't make very many of these cells) but were most useful at the periphery of the eye. The red and green cone cells, though, would be about equally useful at picking up information from these scenes. That explains why humans can have widely varying ratios of red to green cone cells without an effect on their vision.

Though they may seem disorganized, our retinas have evolved to efficiently gather information from our environment--or our ancestral savanna, anyway. Future research might address how our eyes handle other environments. Additionally, the authors say that knowing how to build eyes efficiently might help us create better robots. Not having had the benefit of evolution, today's robots can't see nearly as well as we can.

Photos: University of Pennsylvania.

Bees and Other Stocking Stuffers

Happy holidays! Inkfish found some exciting goodies in its many-tentacled stocking this year (thanks, tipsters!), including:


Toys for chimpanzees
While observing a chimpanzee community in Uganda for 14 years, researchers Sonya Kahlenberg and Richard Wrangham saw the animals use sticks in several different ways. They poked narrow sticks into holes to search for water or honey; they threatened other chimps with sticks, or used them for hitting or throwing. Perhaps most surprisingly, they saw some chimps carrying branches or chunks of bark in a way that suggested carrying a doll.

The behavior was seen most often in young female chimps. Because the chimps sometimes carried their sticks into their nests or played with them in a maternal way, the researchers think the stick-carrying behavior is really play-mothering. And since adults don't carry sticks, the young chimps in this community are learning the behavior from each other.

Coyote cops

The city of Chicago is perfectly aware that several dozen coyotes are roaming the parks and streets at night (even, in this video, trotting down the center of State Street, in the loop). In fact, the coyotes are out with the government's blessing. 

Cook County has put radio collars on more than 60 coyotes and allows them to run around Chicago without interference. This lets the Coyote Project gather data about how coyotes travel, while the animals themselves get to kill all the rats they want. And, um, only an occasional house cat.

Adorable pocket-sized scientists (with bonus bees!)

A group of 8- to 10-year-old students at Blackawton Primary School in the United Kingdom are probably the youngest researchers ever to be published in a peer-reviewed journal. 

Teacher Dave Strudwick and neuroscientist Beau Lotto led the kids in an awesome classroom study about bees. The students wanted to study whether bees could use spatial reasoning to solve a puzzle. So they presented the bees with different arrangements of colored circles, some holding sugar water, and concluded that the bees did learn which patterns were the best "flowers" to visit.

The students' paper was published in Biology Letters. It includes many samples of the students' own language, such as the confusing statement, "We then put the tube with the bees in it into the school's fridge (and made bee pie :))...No bees were harmed during this procedure," as well as the heartening conclusion that "Science is cool and fun because you get to do stuff that no one has ever done before." 

Volcanoes made out of ice
Based on images and data from Cassini, a spacecraft orbiting Saturn, scientists think that Titan (one of Saturn's moons) has Earth-like volcanoes on its surface. Unlike Earth volcanoes, though, these volcanoes might spew ice. Take that, Eyjafjallajokull!

A new family member
Did you ever ask your parents for a baby sister or brother for Christmas? How about a new cousin? In Denisova Cave in Siberia, researchers found a 30,000-year-old finger bone. They managed to sequence its DNA, and concluded that it belonged to a previously unknown human relative. 


These ancient people, the "Denisovans," were more closely related to Neanderthals than to Homo sapiens. Though the Denisovans lived at the same time as modern humans, they're long extinct, along with Neanderthals and the "hobbit" people that may have lived on the island of Flores. We still don't know what became of our ancient cousins, leaving us the only hominids around. But a tiny bit of Denisovan DNA seems to persist in the genomes of Melanesians--a gift they didn't know they'd gotten.




Images: cell.com, rsbl.royalsocietypublishing.org, NASA/JPL-Caltech/USGS/University of Arizona

Optimism and Pessimism (a quiz)

Does everybody have a sharpened pencil?

1. A scary new type of drug-resistant bacteria has emerged in the UK. It appears to have come from____, where British people are traveling to _____.

a. Thailand/receive experimental stem cell treatments

b. America/take advantage of the weak dollar

c. Morocco/stay in Sex-and-the-City-2-themed hotels

d. India/have cosmetic surgery

2. Meanwhile, the World Health Organization has declared that the H1N1 (swine flu) pandemic is:

a. now peaking in the southern hemisphere

b. leading to a secondary pneumonia pandemic

c. just a lot of hype

d. over

3. If you're home with the flu, why not occupy yourself with a Rubik's cube? After 15 years of research, a programmer has determined that any Rubik's cube can be solved in just:

a. 80 moves

b. 50 moves

c. 20 moves

d. 15 moves

4. You already knew that orangutans are bad dieters, but did you know that they're also excellent at charades? This week, scientists published an overview of pantomimes they've seen orangutans act out. Which of the following was NOT included?

a. "I'd like a haircut."

b. "Your fly is open."

c. "Hurry up and open this coconut for me."

d. "Wipe that dirt off your face."

5. Earlier this year, Stephen Hawking made the surprising assertion that we shouldn't try to contact extraterrestrials, because intelligent aliens are probably mean. This week, in another bizarre blend of scientific optimism and pessimism, he said that:

a. If we can just avoid wiping ourselves out for another 200 years or so, humans will be able to survive by colonizing other planets.

b. HIV is going to solve the planet's overpopulation problem.

c. After global warming melts the ice caps completely, the ocean will be able to absorb a lot more carbon.

d. Humans will probably invent time travel shortly before our civilization collapses, thereby allowing someone to go back in time and warn us.

Answers are in the comments.

Pokey Pongo

Pity the Pongo who tries to go on a diet. Scientists announced this week that orangutans (their genus name is Pongo) have the slowest metabolism of almost any mammal. Pound for pound, they use less energy than mammals "including sedentary humans," as researchers noted with amazement.

How do you measure an orangutan's energy use? First, you feed it heavy water. Then you need to get it to pee in a cup. Luckily, captive orangutans at the Great Ape Trust in Iowa are pretty agreeable. "We walked around with some little paper Dixie cups and just held them under the ape and asked them if they would pee in the cup for us," says Washington University anthropologist Herman Pontzer.

Pontzer thinks orangutans have evolved super-slow metabolisms because, in the wild, they survive on fruit that can be scarce for much of the year. I'd be interested to know, though, how similar the captive orangutans really are to wild ones. The researchers say that the captive orangutans have "activity levels similar to orangutans in the wild." But surely there are other factors that could affect the metabolism of these animals, which are close relatives to humans. The types of activity they get, their stress levels, the regularity of their feeding, and their degree of interaction with other orangutans must all be different in captivity from in the wild. Just think of all the factors (according to your average women's interest magazine, anyway) that can affect human metabolism!

Even if the captive apes have a slower metabolism than their wild counterparts, it's still an impressive feat. The only mammal with a slower measured metabolism is the tree sloth. Like an orangutan, a sloth hangs out in trees a lot (often upside-down, in the case of the sloth) and has goofily long arms. Both animals are big dozers.

The sloth moves at an especially unhurried pace: somewhere around 2 meters per minute. So much for cardio!