When a pollinator is at your front steps about to come in for a drink of nectar, you'd be foolish to let a gust of wind blow her away. That's why most flowers have installed velcro doormats. Pointy cells give their petals an extra-grippy surface that encourages bees, even in the middle of a windstorm, to stop and stay a while.
Flowers such as roses, tomatoes, and petunias have cone-shaped cells in the surface of their petals. In fact, about 80 percent of flowers with traditional petals have these conical cells, says University of Cambridge plant scientist Beverley Glover. The cones make a flower's color appear more vibrant by focusing sunlight onto pigment held in the center of the cell. They also help bees latch on. Since the cells are about the same size as the tiny claws on bees' feet, the claws slide in between the cones for a tight grip.
Previous research has shown that conical cells help bumblebees get the nectar out of snapdragons. These flowers keep their goods hidden inside what looks like a hinged door (or apparently, if you're the person who named this flower, a dragon's mouth). Snapdragons with pointed petal cells let bees comfortably land, pry open the door, and drink the nectar. When bees visit mutant snapdragons with flat petal cells, they struggle to maintain their grip.
But snapdragons, with their elaborate structure, are an unusual case. So Glover's team set out to see what conical cells are doing in simpler flowers. They started with the ordinary petunia.
When the team presented bumblebees with both standard petunias and mutant (flat-celled) petunias, the bees preferred to visit the more velcro-esque flowers. The difference in color between the two purple flowers was too slight for a bee's eyes to detect, so something else about the conical cells must have been attracting them.
To find the attractive quality in grippy petunia petals, the researchers swapped their standard petunias for a grippy petunia that's unattractive. This genetic mutant has the usual cone-shaped cells, but a much darker purple color that makes the flower difficult for bees to see. Now the bees preferred the flat-celled flowers, since they were easier to find and fly to.
Then the team created a little wind to see whether it gave the upper hand back to cone-celled flowers. Or rather, they created the appearance of wind by placing their petunias on a laboratory shaking machine. This device has a platform that jostles its contents around, keeping tubes and beakers of things well-mixed during experiments. When loaded up with petunias, it waved the flowers as if they were outside in a stiff breeze. (To add to the illusion, the shaker was covered with green tissue paper.)
At first, the bees still flew to the lighter-colored flowers with flat cells. But over the course of the 100 flower visits researchers let each bee make, the bees learned to favor the conical-celled flowers, even though they were still harder to see. By the end of the experiment, bees flew to these flowers a majority of the time.
Not only do conical cells help bees grip flowers, but they become even more important when those flowers are moving. The bumblebees' desire for a comfy place to wedge their feet overcame their dislike of difficult-to-see colors.
If pointed cells on your petals is so great, why do flowers such as lilies, tulips, and magnolias have flat cells instead? Glover says this is a question she's still trying to answer. "In a couple of plant groups we've been studying, we do think we see an association between switching to moth or bird pollination and losing your conical cells," she wrote in an email. If your pollinator is an insect or hummingbird that hovers over you rather than landing, there may be no advantage to keeping a sticky doormat.
Another possibility is that slippery-petaled flowers encourage bees to ignore the doorstep altogether and fly straight in the window. In flowers such as the flat-celled woody nightshade, Glover says, "the bee grasps the anthers and vibrates them to get the pollen out." But, she adds, "we don't have data to support this idea yet." When it comes to pollination etiquette, we're still learning the rules.
Alcorn, K., Whitney, H., & Glover, B. (2012). Flower movement increases pollinator preference for flowers with better grip Functional Ecology DOI: 10.1111/j.1365-2435.2012.02009.x
Images: Bee on flower by Martin Cathrae/Flickr; experimental diagram by Alcorn et al.
When you're surrounded by an ocean full of potential predators, the best way to avoid seeing the inside of one's stomach is to make sure none of them see you in the first place. Octopuses and some other cephalopods are experts at camouflage, manipulating the colors and textures of their skin to hide in plain sight. But their strategy, it turns out, has nothing to do with disappearing into the background.
To learn the camouflaging secrets of the masters, researchers led by Noam Josef at Ben-Gurion University of the Negev in Israel went scuba diving. On reefs in the Red Sea and Tyrrhenian Sea, they snapped pictures of two octopus species (Octopus cyanea and O. vulgaris) whenever they saw an individual hiding—crouched low and motionless for a minute or longer.
For the pictures to work in the team's digital image analysis, they had to be sunlit just so and taken from directly above. Over three years, they captured just 11 photos that fit their criteria. "These images are a bit hard to get," Josef said in an email. Not to mention the challenge of finding a camouflaged octopus in the first place.
Hint: Look for the coral with tentacles.
Each bird's-eye, or rather shark's-eye, photo was converted to a grayscale image. Researchers selected a rectangle showing the pattern on the octopus's mantle (the part that's not tentacles). Then a software algorithm compared the mantle sample to rectangles from everywhere else in the photo, shifting the frame one pixel at a time and searching for a match.
The best matches to the octopuses' camouflage patterns were not to be found in the gravelly ground beneath them. Instead, 10 out of the 11 octopuses had clearly mimicked a specific object nearby. They played coral, rock, weird sand blob, or algae patch.
View this picture larger and you'll see that one coral has eyes on top.
A camouflaged animal's best strategy depends on the viewpoint of its predators. Many fish have light-colored bellies that blend in with the sky when seen from below. Certain pygmy sharks take this trick a step further and emit a blue glow from their undersides. When viewed from above, fishes' darker-colored backs vanish into the background of the ocean.
An octopus sitting on a reef has to worry about big fish hunting from above, as well as moray eels and other predators that creep up from the sides. Since these enemies approaching from different angles will see the octopus framed against different backdrops, maybe it makes sense for the octopus to forgo blending in altogether. It's stuck being obvious, so it may as well pose as an obvious object that's less edible.
"Sometimes octopuses make an honest mistake and simply become conspicuous" by camouflaging, Josef says. "However, in a complex environment like the coral reef, acquiring key features of an object may serve the octopus better than just matching the general look of the reef." You can see a few of those convincing key details in the photos above, where octopuses have contorted themselves into the knobby branches of a coral or a shell's striped ridges.
Scientists have discovered some of the specialized cells in octopus skin that help them pull off their elaborate imitations—pigment holders, reflectors, light scatterers. But Josef says there are still more questions than answers: "What visual cues are used by these animals? How do octopuses match their colors even though they're colorblind?" (Yes. Colorblind.) "What information is transmitted from the eye to the brain? And what does an octopus really see?"
We're still "far from understanding" the camouflaging act of the octopus, Josef says. We'll have to keep hunting for scraps of information the cunning cephalopods let slip. That is, assuming we can find them first.
Josef, N., Amodio, P., Fiorito, G., & Shashar, N. (2012). Camouflaging in a Complex Environment—Octopuses Use Specific Features of Their Surroundings for Background Matching PLoS ONE, 7 (5) DOI: 10.1371/journal.pone.0037579 Images: Top, Ms. Keren Levy. Middle and bottom, Mr. Zvika (Ziggy) Livnat.
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
When coming face-to-face with a wriggling, freshly born pile of poisonous snakes, most of us wouldn't linger for a close look. But it was by looking into these living linguini platters that one biologist found a new answer to an old question: Why does island life make animals such freak shows?
Some big-bodied species shrink when they move from the mainland to an island habitat, a phenomenon that's created pygmy sloths, miniature mammoths, and possibly even a dwarf hominid that's now extinct. Some small-bodied species, meanwhile, grow enormous on islands. This category includes a 3-inch-long earwig, various ungainly and flightless birds, and a giant rat (living on Flores, the same island where the miniature people were, unfortunately for them).
Scientists have explained these fun-house transformations with a lack of resources on an island (keeping animals smaller) or a lack of predators (allowing them to grow bigger). Other factors, such as distance to the mainland or one sex's preference for extreme traits in a mate, could be at work too.
French researcher Fabien Aubret wondered whether scrutinizing the sizes of adult animals was making scientists miss another important variable: the size of babies. A newborn animal that can't find its first meal will quickly exit the gene pool. In snakes, this could be a simple matter of not being able to get one's mouth all the way around one's prey to swallow it.
Aubret studied twelve populations of tiger snakes, some living on mainland Australia or Tasmania and others on nearby islands. Among the island exiles, some groups have grown giant--up to 1.5 meters long, rather than the usual 0.8 or 0.9 meters--while others have shrunk. Most of the island populations were stranded by rising seas six to ten thousand years ago, leaving them with a different selection of prey animals than on the mainland.
Armed with a measuring tape, Aubret asked whether the changes the snakes' bodies have undergone since then can be entirely explained by the need for newborns to get their jaws around a meal. Tiger snake mothers give birth to live young rather than laying eggs, popping out a dozen or more at a time. On the mainland, these snakes and their parents swallow frogs for most of their meals. But on the islands, their prey can range from little lizards to large nesting seabirds.
Aubret captured almost 600 adult snakes from the various populations, measuring their length and weight before releasing all of them except the pregnant females. When the tangles of baby snakes emerged, he monitored the newborns' sizes for six months while feeding them a standard diet. For each study site, he calculated the average weight and circumference of animals on the prey buffet. (Weight because first a snake must subdue the unfortunate gecko or skink, and circumference because the animal must fit down the gullet.)
The size of baby snakes from each site--and the size of their jaws--was closely tied to the weight and circumference of the prey animals available there. Baby snakes from sites with large prey also grew faster.
Aubret says the pressure on newborn snakes to swallow available prey might be the only explanation necessary for the various body sizes tiger snakes have evolved on different islands. Adult body size, though of course it's related to the size of newborns, might be mainly irrelevant.
This gives biologists a new clue to the puzzle of how island life makes animals shrink or grow. While they wrap their heads around that, the tiger snakes will continue to wrap their own heads around any slow-moving animal that fits.
Fabien Aubret (2012). Body-Size Evolution on Islands: Are Adult Size Variations in
Tiger Snakes a Nonadaptive Consequence of Selection on Birth Size? The American Naturalist, 169 (6)
Image: Not actually a tiger snake, by batwrangler/Flickr
A superior visual memory is the best friend of artists and competitive card memorizers. But to people who've lived through traumatic events, it might be the enemy.
Researchers in Switzerland and Germany guessed that people with a better memory might be more susceptible to post-traumatic stress disorder, their minds clinging stubbornly to horrific events in the past. But studying the memories of people living with a mental illness is difficult, since the disorder itself might affect their memory. So when the researchers went on a hunt for genes that are linked to both memory and PTSD, they began in a healthy population.
A group of more than 700 Swiss young adults, free of any mental illness, participated in the first part of the study. They viewed several dozen pictures that were meant to elicit either a positive emotional response, a negative emotional response, or a neutral one. After being distracted for 10 minutes, they were given a surprise quiz on how many of the pictures they could recall.
The subjects's DNA underwent testing too. The researchers checked 2,005 individual spots in each person's genes called SNPs (pronounced "snips"). These are bits of DNA that vary across a population, such that some people might have a T nucleotide where others have a G, for example. All of the 2,005 SNPs the researchers checked had to do with certain multitasking molecules called protein kinases that seem to be involved in memory formation.
Out of the 2,005 gene variants in this haystack, one needle emerged: a bit of DNA that was significantly linked to subjects' performance on the memory test. There are two versions (or alleles) of the gene in question, which makes a molecule called PKC alpha. People with one of these alleles--an A rather than a G--remembered more of the pictures they'd seen. Although researchers were especially interested in their subjects' recall of emotionally negative pictures, the effect seemed to extend to positive and neutral ones as well.
Brain scans showed a difference inside the heads of these high-performing memorizers. Subjects with A alleles had more activity in parts of the prefrontal cortex while looking at the negative images. These same regions, the authors say, have been linked to emotional memory storage in other studies.
Now that the researchers had found a gene of interest, they could study it in some actual traumatized people. They turned to a group of 347 Rwandan refugees who fled their country during the civil war. After being interviewed thoroughly, 134 of the refugees were found to meet criteria for post-traumatic stress disorder. Rwandans who had the better-memory gene variant from the first part of the study were more likely to be in the PTSD group. They were also more likely to have the symptom of reliving a traumatic memory over and and over.
Among the healthy Swiss population, the better-memory A allele was more common than the worse-memory G allele. But among the Rwandan refugees, the opposite was true: The better-memory gene variant was the rare one. If it were more common, PTSD symptoms might have been even more frequent among the displaced Rwandans.
The genetics of mental illness are tricky to untangle, and what merits a diagnosis in one culture might be normal in another. Studies such as this one, though, could reveal who's most at risk for certain symptoms. And if scientists can figure out how exactly the genes in question are acting in the brain, we might see new drugs that can treat some of these symptoms--or prevent people's memories from turning against them in the first place.
de Quervain, D., Kolassa, I., Ackermann, S., Aerni, A., Boesiger, P., Demougin, P., Elbert, T., Ertl, V., Gschwind, L., Hadziselimovic, N., Hanser, E., Heck, A., Hieber, P., Huynh, K., Klarhofer, M., Luechinger, R., Rasch, B., Scheffler, K., Spalek, K., Stippich, C., Vogler, C., Vukojevic, V., Stetak, A., & Papassotiropoulos, A. (2012). PKC is genetically linked to memory capacity in healthy subjects and to risk for posttraumatic stress disorder in genocide survivors Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1200857109
Naturally a mother bat is happy to welcome into the world a bouncing baby whatever, as long as it has all its fingers and toe-claws. But she also wants her little one to have every advantage she can give it. So when spring comes early, big brown bats prefer to keep their female embryos. Unwanted males are reabsorbed into their mothers' bodies as if they never existed.
University of Calgary biologist Robert Barclay learned the bats' secret by spying on three colonies living in the charmingly named city of Medicine Hat, Alberta. The bats roost in the attics of elementary-school buildings. Over the course of 15 years, Barclay snagged the bats in nets at night or plucked them from their roosts among the attic beams to examine them.
Since females return to their birth colony every year to breed, while males disperse, these colonies mainly held mothers and babies. Barclay was able to track which females were pregnant and what kinds of babies they had--and when.
"When" turned out to be the important question. Overall, the Eptesicus fuscus bats gave birth to equal numbers of male and female babies. But certain springs turned out a glut of girl bats, nearly twice as many as boys. By later in the summer, the ratio evened out again.
What was special about these girl-heavy springs, Barclay found, was that the whole colony gave birth earlier than usual. "The entire birth period shifts from year to year, depending on the weather," he wrote in an email. "When it is cold and damp in the spring and there are not many insects for the bats to feed on, the pregnant mother bats drop their body temperature to save energy and wait out the bad weather." This waiting period is called torpor, "a sort of shorter version of hibernation," Barclay says. In addition to lowering the mother's body temperature, it slows the growth of the embryo inside her. It was in the warmest springs, when mothers could end their torpor early, that they favored girls.
Biology says that mothers should skew the sex ratio of their offspring when it will let them pass on their own genes most effectively. A male baby bat won't give his mother any grandchildren until his second year of life, regardless of when he's born. However, "if a mother gives birth to a female baby early enough in the summer for it to be able to grow and put on enough fat for the winter," Barclay says, "that baby will be able to produce her own baby the next summer, as a 1-year-old." Having an extra year's worth of grandchildren is a major evolutionary benefit for a mother bat.
What gives girls a head start on reproduction is the bats' weird way of breeding. Mating happens in the fall and winter, while the bats born that spring and summer are still juveniles--and the young males haven't yet started making sperm. But female bats don't ovulate until the spring. At that point, the male contribution she's stored all winter finally fertilizes her eggs. This means female bats, if they're born early enough, can ovulate and give birth within their first year of life.
Big brown bats have just one baby at a time. But several eggs are fertilized and implant in the mother at once. At some unknown point during gestation, she reabsorbs all but one of those developing embryos into her body. However it happens, evolution has given mother bats the power to choose a female embryo over the others when spring arrives early.
Bats are far from the only species capable of skewing their babies' sex ratios. Other mammal and bird species have been observed giving birth to extra male or female offspring at certain times, depending on their own set of influencing factors. Even humans, it's been suggested, can bias their birth ratios based on life expectancy or parents' wealth or the weather. The mechanisms are mysterious, but evolution will always favor moms whose children produce more grandchildren.
Whatever secrets they're still keeping, the attic bats have taught their young downstairs neighbors a few things about biology. "When we worked in the schools we would give talks to the students about bats, the importance they have in the environment, and how cool it was that they had bats right in their own school," Barclay says. "We frequently had kids come in the evening to watch the bats as they exited to go and feed." One of the hundred-year-old schools is named Elm Street, as in Nightmare on. "A great place to study bats on a dark, moonless night!" Barclay adds.
Even spookier than attic bat colonies is the reminder that our species' whole evolutionary history had a hand in determining whether we were born. We, and the bat babies, should probably thank our moms.
Barclay, R. (2012). Variable Variation: Annual and Seasonal Changes in Offspring Sex Ratio in a Bat PLoS ONE, 7 (5) DOI: 10.1371/journal.pone.0036344
Images: Big brown bat by cotinis/Flickr; school building by Robert Barclay.
And every day I've been surprised and happy to see you--yes, you--reading, sharing, commenting, liking, tweeting, Stumbling and Digging (the last two are especially appropriate, given my propensity for poop stories). Thank you.
If you want to celebrate with Octopus and me, why not comment on a post sometime? We'd love to hear your voice. Or send a story to a friend! The more the merrier, as I'm pretty sure they say under the ocean. Unless you're a top predator species or something that lives alone under a rock.
A sperm cell, much like an expensive robotic vacuum cleaner, is a minimally intelligent body on a mission. Both the Roomba and the male gamete have to navigate a walled space without much idea where they're going or why. And although it won't clean your floors on the way, the sperm cell uses some of the same strategy as the robot vacuum.
To discover the set of rules that sperm cells steer by, researchers used--what else?--sperm mazes. Led by fluid dynamics researcher Petr Denissenko at the University of Warwick, a group of scientists in the United Kingdom built hair-thin tunnels in various shapes. Then they sent human sperm into the curving or zigzagging tunnels. A camera watched through a glass wall on each channel to see what paths the tiny explorers took.
In a narrow tunnel, frantically swimming sperm soon come up against a wall. Then, the camera showed, they follow that wall, seeming to keep their heads against it as they swim. (This same trick will get you out of a corn maze if you're lost, though you might want to keep a hand on the wall instead of your head.)
Wall-following is also one of the rules used by a Roomba. In the case of the robot, it ensures that the edges of the room and the base of the sofa get clean. In the case of sperm, wall-following keeps them moving in one direction as they trace the twists and folds of a fallopian tube.
But sperm aren't experts. When the wall takes a sharp turn away from them, sperm often don't notice; they simply shoot off in the direction they were already swimming. Luckily, they'll find another wall soon. "There are no large open spaces in the reproductive tract," Denissenko says.
Not all sperm are equally spacey about following walls. When the path bends, some follow it better than others. If future research finds a connection between wall-following skill and sperm success--are better navigators also better fertilizers?--then fertility doctors might be able to sort out the best sperm using mazes.
Knowing the rules that sperm swim by also means doctors can coax all of them to travel in the same direction. Denissenko and his coauthors built another maze, shaped like a wreath of grapes, that herds sperm into U-turns until they're all swimming one way.
Roombas use other rules that sperm don't. For example, a Roomba knows to avoid cliffs, a hazard human sperm are unlikely to encounter since there are no staircases inside a human.
Sperm have their own rule too: When they collide with each other, they swim off in different directions. Is this a trick for getting out of traffic? And how do sperm cells know they've hit a fellow swimmer, rather than a wall? Scientists aren't sure yet. "Understanding the role of collisions is really on my to-do list now," Denissenko says.
Like cat-harassing robots, humans' own little automatons rely on a few simple algorithms to do their job. It's nice to see that these seemingly clueless cells know a thing or two. Now if only they'd take on some household chores.
Denissenko, P., Kantsler, V., Smith, D., & Kirkman-Brown, J. (2012). Human spermatozoa migration in microchannels reveals boundary-following navigation Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1202934109
Those of us without prehensile ears tend to think of our senses of hearing and touch as separate. But our sensory abilities overlap with each other more often than our kindergarten teachers let on. Our sense of smell gets help from our vision centers. Tasting food is mostly done with our noses. And a new study says hearing is just another sense of touch. The same genes can make you good--or deficient--at both.
Hearing a bird chirp and picking up a pencil from your desk, though they seem like wildly different tasks, are really the same trick performed by your body twice. Cells that receive physical input from the outside world (the edge of the pencil against your fingertips, or the vibration of sound waves rattling your inner ear) have to turn that information into an electrical signal and send it back to your brain.
So researchers in Germany guessed that the same genes affect both senses, in people as well as in other vertebrates. They used human subjects to ask the question in several different ways.
First, the team studied a group of more than 500 hearing subjects. In a battery of tests, people listened to tones and clicks, responded to tiny vibrations on their fingertips (measuring their touch sensitivity), and felt surfaces with narrow ridges (touch acuity).
There was plenty of variability in subjects' hearing and touch abilities. Both senses clearly grew worse with age. And in many of the tests, women outperformed men. These data let researchers chart how a healthy person's senses should act throughout their lives.
Then 100 pairs of twins came in for testing. Geneticists love twins: Identical sets have all the same genes, so any differences between them must come from somewhere outside their DNA. Fraternal sets share about half their genes, but are the same age and grew up (usually) in the same environment, so they can be easily compared to identical twins.
Subjecting the twin sets to the same tests, the researchers saw that touch sensitivity and touch acuity both have major genetic components, just like hearing does. And they saw that the two senses correspond to each other: People with good hearing are more likely to have good sense of touch too.
What about people with bad hearing? The researchers recruited another set of 39 teenagers and young adults from a school for the hearing impaired. About a fifth of the deaf subjects had "very poor touch performance."
There are plenty of genetic and non-genetic reasons people are born deaf, and the researchers don't know which of these factors were present in their subjects. But it seems that for some hearing-impaired people, whatever damaged their hearing did the same to their sense of touch. The simple explanation is that the same genetic mutation affects both senses.
Finally, the researchers examined a group of subjects with an illness called Usher syndrome that causes deafness and blindness. Scientists know of several genes that are involved--a mutation in any one of then can cause Usher syndrome. The German team found that patients with a certain Usher gene mutation also had significantly worse touch acuity than normal.
The twins and the deaf young adults showed that hearing and touch go along with each other, seeming to rely on shared genes. The Usher syndrome patients let researchers go a step further and identify one specific gene that affects both senses. "Both senses require cells that convert tiny changes in mechanical force into an electrical signal," said senior author Gary Lewin. "Genes may code for proteins that play a similar role in this process in the two types of cells." In other words, if our cells use the same genes for hearing and touch, they may also share a set of molecular tools.
I asked Lewin whether science is on the path to trimming down our number of senses. If we begin to understand hearing and touch as one mechanism, and if taste barely exists without smell, do we really have three senses? "No, I think we will stick with five and even more senses," Lewin said. "The cellular mechanisms and the way these different sensory cells are connected are highly unique."
Even so, our sensory skills continue to surprise us. Our kindergarten teachers may not have been wrong, but our understanding of human senses is growing up.
Frenzel, H., Bohlender, J., Pinsker, K., Wohlleben, B., Tank, J., Lechner, S., Schiska, D., Jaijo, T., Rüschendorf, F., Saar, K., Jordan, J., Millán, J., Gross, M., & Lewin, G. (2012). A Genetic Basis for Mechanosensory Traits in Humans PLoS Biology, 10 (5) DOI: 10.1371/journal.pbio.1001318