Chapter 6. Evolution of the Brain and Behavior
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
By Sarah Kaplan The ancient Greeks spoke of a mythological society composed entirely of warrior women. The medieval traveler John Mandeville wrote of a place whose female rulers "never would suffer man to dwell amongst them." "Paradise Island," home of Wonder Woman, was a feminist utopia where no one with a Y chromosome was allowed. Sadly, those places only exist in fiction. But something like them does exist in the real world. It's in a wetland in rural Ohio. And it's full of salamanders. "They’re pretty incredible," said Robert Denton, a biologist at Ohio State who studies an unusual group of salamander species that literally don't need men. These creatures – all female – reproduce by cloning themselves. To keep their gene pool diverse, they sometimes "steal" sperm left behind on trees and leaves by male salamanders of other species and incorporate that DNA into their offspring. Most sexually reproducing organisms have two sets of chromosomes to make up their genome – one from each parent. But one of these strange salamanders can have between two and five times that much genetic material lying in wait within her cells. It's as if they have multiple genomes to fall back on, and that's made them incredibly successful. "Polyploid" salamanders have been around some 6 million years, Denton said — far longer than most other animal species that reproduce asexually. Since a lack of diversity means having a smaller arsenal of genetic variation to fall back on when living conditions change, these groups usually go extinct relatively quickly. © 1996-2016 The Washington Post
by Susan Milius There’s nothing like a guy doing all the child care to win female favor, even among giant water bugs. Thumbnail-sized Appasus water bugs have become an exemplar species for studying paternal care. After mating, females lay eggs on a male’s back and leave him to swim around for weeks tending his glued-on load. For an A. major water bug, lab tests show an egg burden can have the sweet side of attracting more females, researchers in Japan report May 4 in Royal Society Open Science. Given a choice of two males, females strongly favored, and laid more eggs on, the one already hauling around 10 eggs rather than the male that researchers had scraped eggless. Females still favored a well-egged male even when researchers offered two males that a female had already considered, but with their egg-carrying roles switched from the previous encounter. That formerly spurned suitor this time triumphed. A similar preference, though not as clear-cut, showed up in the slightly smaller and lighter A. japonicus giant water bug. “We conclude that sexual selection plays an important role in the maintenance of elaborate paternal care,” says study coauthor Shin-ya Ohba of Nagasaki University. © Society for Science & the Public 2000 - 2016
By Emily Benson Baby birds are sometimes known to shove their siblings out of the nest to gain their parents’ undivided attention, but barn owl chicks appear to be more altruistic. Scientists recorded the hissing calls of hungry and full barn owl nestlings (Tyto alba, pictured), then played the sounds back to single chicks settled in nests stocked with mice. The young owls that heard the squawks of their hungry kin delayed eating each rodent by an average of half an hour; those that heard cries indicating their invisible nest-mate was full ate the mice more quickly. The findings suggest that barn owl chicks give hungrier siblings a chance to eat first even when the nest is full of food, the researchers will report in an upcoming issue of Behavioral Ecology and Sociobiology. So is it true altruism? Maybe not. Nestlings may share food in exchange for help with grooming or to get the first crack at a later meal, the team says, suggesting a possible ulterior motive. © 2016 American Association for the Advancement of Science
Link ID: 22174 - Posted: 05.04.2016
By ERICA GOODE Horses snooze in their stalls. Fish take their 40 winks floating in place. Dogs can doze anywhere, anytime. And even the lowly worm nods off now and then. All animals, most scientists agree, engage in some form of sleep. But the stages of sleep that characterize human slumber had until now been documented only in mammals and birds. A team of researchers in Germany announced in a report published on Thursday, however, that they had found evidence of similar sleep stages in a lizard: specifically, the bearded dragon, or Pogona vitticeps, a reptile native to Australia and popular with pet owners. Recordings from electrodes implanted in the lizards’ brains showed patterns of electrical activity that resembled what is known as slow-wave sleep and another pattern resembling rapid eye movement, or REM, sleep, a stage of deep slumber associated with brain activity similar to that of waking. Some researchers had argued that these stages were of relatively recent origin in evolutionary terms because they had not been found in more primitive animals like amphibians, fish, reptiles other than birds, and other creatures with backbones. But the new finding, said Gilles Laurent, director of the department of neural systems at the Max Planck Institute for Brain Research and the principal author of the study, “increases the probability that sleep evolved in all these animals from a common ancestor.” He added that it also raised the possibility that staged sleep evolved even earlier and that some version of it might exist in animals like amphibians or fish. The report appeared in Thursday’s issue of the journal Science. Other researchers said the study could help scientists understand more about the purpose and mechanisms of sleep. But the finding, they added, is bound to generate more controversy about whether the resting state of primitive animals is really the same as sleep, and whether the brain activity seen in a lizard can be compared to that in mammals. © 2016 The New York Times Company
Nicola Davis Benedict Cumberbatch’s deep and booming voice might have made him a hit among women, but a low pitch is more likely to have evolved to intimidate other men, new research suggests. When both heterosexual men and women were played recordings of male voices, the deeper tones were hailed by men as sounding more dominant. While the deeper voices were judged to be more attractive by female listeners, the effect was weaker, the researchers report. “If you look at what men’s traits look like they are designed for, they look much better designed for intimidating other males than for attracting females,” said David Puts of Pennsylvania State University, who led the study. Published in Proceedings of the Royal Society B: Biological Sciences, the three-part study by an international team of scientists explored the links between voice pitch and mating systems, attractiveness and, for males only, perceived dominance. A formula for the perfect voice? Read more In the first leg of the research, the scientists turned their attention to primates encompassing Old and New World monkeys, as well as humans and other apes, to explore differences in “fundamental frequency” between males and females of each species - the aspect of the voice that is perceived as pitch. After selecting 1721 recordings, they found large differences were more common in polygynous species - where males mate with more than one female - than monogamous ones. That, they say, could be because in polygynous species, competition between males is greater - hence a male with a lower-pitched voice deemed to be intimidating could have the edge in securing a mate. Intriguingly, the researchers found that among the apes humans showed the greatest difference in pitch between the sexes, suggesting our ancestors were not searching for “the one” but were polygynous - a situation Puts still believes to be the case. © 2016 Guardian News and Media Limited
Cassie Martin The grunts, moans and wobbles of gelada monkeys, a chatty species residing in Ethiopia’s northern highlands, observe a universal mathematical principle seen until now only in human language. The new research, published online April 18 in the Proceedings of the National Academy of Sciences, sheds light on the evolution of primate communication and complex human language, the researchers say. “Human language is like an onion,” says Simone Pika, head of the Humboldt Research Group at the Max Planck Institute for Ornithology in Seewiesen, Germany, who was not involved in the study. “When you peel back the layers, you find that it is based on these underlying mechanisms, many of which were already present in animal communication. This research neatly shows there is another ability already present.” As the number of individual calls in gelada vocal sequences increases, the duration of the calls tends to decrease — a relationship known as Menzerath’s law. One of those mechanisms is known as Menzerath’s law, a mathematical principle that states that the longer a construct, the shorter its components. In human language, for instance, longer sentences tend to comprise shorter words. The gelada study is the first to observe this law in the vocalizations of a nonhuman species. “There are aspects of communication and language that aren’t as unique as we think,” says study coauthor Morgan Gustison of the University of Michigan in Ann Arbor. © Society for Science & the Public 2000 - 2016
By Sarah Kaplan We know where the human story started: In Africa, millions of years ago, with diminutive people whose brains were just a third of the size of ours. And we know where it ended: with us. Yet a lot of what happened in between is still debated, including the question of how humans' bodies and noggins got so much bigger than our ancestors'. The traditional thinking is that the growth of both was spurred by the process of natural selection. The evolutionary advantages of a big body and a big brain are plentiful, so it seems reasonable to think that each developed independent of the other in response to the demands of survival in a hostile world. But a new study in the journal Current Anthropology suggests that, while our brains are certainly an advantageous adaptation, our imposing physiques (such as they are) are more of an evolutionary fluke. That's because the genes that determine brain and body size are the same, argues Mark Grabowski, a fellow at the American Museum of Natural History. So as humans evolved bigger and bigger brains, our bodies "just got pulled along." Grabowski acknowledges that it may seem like a counterintuitive conclusion — most of us learned in high school biology that evolution is about adapting to circumstances and that only the fittest survive. We're not used to thinking of traits as a product of happenstance. But evolutionary scientists know that lots of traits — even ultimately beneficial ones — are just the luck of the draw.
Link ID: 22119 - Posted: 04.20.2016
By Robin Wylie Bottlenose dolphins have been observed chattering while cooperating to solve a tricky puzzle – a feat that suggests they have a type of vocalisation dedicated to cooperating on problem solving. Holli Eskelinen of Dolphins Plus research institute in Florida and her colleagues at the University of Southern Mississippi presented a group of six captive dolphins with a locked canister filled with food. The canister could only be opened by simultaneously pulling on a rope at either end. The team conducted 24 canister trials, during which all six dolphins were present. Only two of the dolphins ever managed to crack the puzzle and get to the food. The successful pair was prolific, though: in 20 of the trials, the same two adult males worked together to open the food canister in a matter of few minutes. In the other four trials, one of the dolphins managed to solve the problem on its own, but this was much trickier and took longer to execute. But the real surprise came from recordings of the vocalisations the dolphins made during the experiment. The team found that when the dolphins worked together to open the canister, they made around three times more vocalisations than they did while opening the canister on their own or when there was either no canister present or no interaction with the canister in the pool. © Copyright Reed Business Information Ltd.
Eleanor Ainge Roy in Dunedin An octopus has made a brazen escape from the national aquarium in New Zealand by breaking out of its tank, slithering down a 50-metre drainpipe and disappearing into the sea. In scenes reminiscent of Finding Nemo, Inky – a common New Zealand octopus – made his dash for freedom after the lid of his tank was accidentally left slightly ajar. Staff believe that in the middle of the night, while the aquarium was deserted, Inky clambered to the top of his cage, down the side of the tank and travelled across the floor of the aquarium. Rob Yarrell, national manager of the National Aquarium of New Zealand in Napier, said: “Octopuses are famous escape artists. “But Inky really tested the waters here. I don’t think he was unhappy with us, or lonely, as octopus are solitary creatures. But he is such a curious boy. He would want to know what’s happening on the outside. That’s just his personality.” One theory is that Inky slid across the aquarium floor – a journey of three or four metres – and then, sensing freedom was at hand, into a drainpipe that lead directly to the sea. The drainpipe was 50 metres long, and opened on to the waters of Hawke’s Bay, on the east coast of New Zealand’s North Island. Another possible escape route could have involved Inky squeezing into an open pipe at the top of his tank, which led under the floor to the drain. © 2016 Guardian News and Media Limited
By Gareth Cook What are the most intelligent creatures on the planet? Humans come first. (Though there are days when we have to wonder.) After Homo sapiens, most people might answer chimpanzees, and then maybe dogs and dolphins. But what of birds? The science writer Jennifer Ackerman offers a lyrical testimony to the wonders of avian intelligence in her new book, “The Genius of Birds.” There have long been hints of bird smarts, but it’s become an active field of scientific inquiry, and Ackerman serves as tour guide. She answered questions from Mind Matters editor Gareth Cook. What drew you to birds? I’ve watched birds for most of my life. I admire all the usual things about them. Their plumage and song. Their intense way of living. Their flight. I also admire their resourcefulness and pluck. I’ve always been intrigued by their apparently smart behavior, whether learned or innate. I grew up in Washington, D.C. — the second youngest in a gaggle of five girls. My parents had precious little time for one-on-one. Especially my dad, who had a demanding government job. So when he asked me if I wanted to go birdwatching with him one spring morning when I was seven or eight, I jumped at the chance. It was magical, going out in the dark woods along the C&O canal and listening for bird song. My father had learned his calls and songs in Boy Scout camp from an expert, an elderly Greek man named Apollo, so he was pretty good at identifying birds, even the shy woodland species. Eventually he gave me my own copy of Peterson’s Field Guide, along with a small pair of binoculars. I’ve loved birds ever since. My first run in with a clever bird was on our dining room table. We had a pet parakeet, a budgerigar named Gre-Gre, who was allowed to fly around the dining room and perch on our head or shoulders. He had a kind of social genius. He made you love him. But at breakfast, it was impossible to eat your cereal without his constant harassment. He liked to perch on the edge of my bowl and peck at the cereal, flapping his wings frantically to keep his balance, splashing my milk. I’d build a barricade of boxes around my place setting, but he always found a way in, moving a box or popping over the top. He was a good problem-solver. © 2016 Scientific American
By Virginia Morell Moths have an almost fatal attraction to lights—so much so that we say people are drawn to bad ends “like moths to a flame.” But in this age of global light pollution, that saying has a new poignancy: Moths, which are typically nocturnal insects, are dying in droves at artificial lights. The high levels of mortality should have evolutionary consequences, leading to moths that avoid lights, biologists say. To find out, two scientists tested the flight-to-light behavior of 1048 adult ermine moths (Yponomeuta cagnagella, shown above) in Europe. The researchers collected the insects in 2007 as larvae that had just completed their first molt. Three hundred and twenty came from populations that lived where the skies were largely dark; 728 were gathered in light polluted areas. They were raised in a lab with 16 hours of daylight and 8 hours of darkness daily while they completed their life stages. Two to 3 days after emerging as moths, they were released in a flight cage with a fluorescent tube at one side. Moths from high light pollution areas were significantly less attracted to the light than those from the darker zones, the scientists report in today’s issue of Biology Letters. Overall, moths from the light-polluted populations had a 30% reduction in the flight-to-light behavior, indicating that this species is evolving, as predicted, to stay away from artificial lights. That change should increase these city moths’ reproductive success. But their success comes at a cost: To avoid the lights, the moths are likely flying less, say the scientists, so they aren’t pollinating as many flowers or feeding as many spiders and bats. © 2016 American Association for the Advancement of Science.
Link ID: 22100 - Posted: 04.13.2016
By FRANS de WAAL TICKLING a juvenile chimpanzee is a lot like tickling a child. The ape has the same sensitive spots: under the armpits, on the side, in the belly. He opens his mouth wide, lips relaxed, panting audibly in the same “huh-huh-huh” rhythm of inhalation and exhalation as human laughter. The similarity makes it hard not to giggle yourself. The ape also shows the same ambivalence as a child. He pushes your tickling fingers away and tries to escape, but as soon as you stop he comes back for more, putting his belly right in front of you. At this point, you need only to point to a tickling spot, not even touching it, and he will throw another fit of laughter. Laughter? Now wait a minute! A real scientist should avoid any and all anthropomorphism, which is why hard-nosed colleagues often ask us to change our terminology. Why not call the ape’s reaction something neutral, like, say, vocalized panting? That way we avoid confusion between the human and the animal. The term anthropomorphism, which means “human form,” comes from the Greek philosopher Xenophanes, who protested in the fifth century B.C. against Homer’s poetry because it described the gods as though they looked human. Xenophanes mocked this assumption, reportedly saying that if horses had hands they would “draw their gods like horses.” Nowadays the term has a broader meaning. It is typically used to censure the attribution of humanlike traits and experiences to other species. Animals don’t have “sex,” but engage in breeding behavior. They don’t have “friends,” but favorite affiliation partners. Given how partial our species is to intellectual distinctions, we apply such linguistic castrations even more vigorously in the cognitive domain. By explaining the smartness of animals either as a product of instinct or simple learning, we have kept human cognition on its pedestal under the guise of being scientific. Everything boiled down to genes and reinforcement. To think otherwise opened you up to ridicule, which is what happened to Wolfgang Köhler, the German psychologist who, a century ago, was the first to demonstrate flashes of insight in chimpanzees. © 2016 The New York Times Company
Modern humans diverged from Neanderthals some 600,000 years ago – and a new study shows the Y chromosome might be what kept the two species separate. It seems we were genetically incompatible with our ancient relatives – and male fetuses conceived through sex with Neanderthal males would have miscarried. We knew that some cross-breeding between us and Neanderthals happened more recently – around 100,000 to 60,000 years ago. Neanderthal genes have been found in our genomes, on X chromosomes, and have been linked to traits such as skin colour, fertility and even depression and addiction. Now, an analysis of a Y chromosome from a 49,000-year-old male Neanderthal found in El Sidrón, Spain, suggests the chromosome has gone extinct seemingly without leaving any trace in modern humans. This could simply be because it drifted out of the human gene pool or, as the new study suggests, it could be because genetic differences meant that hybrid offspring who had this chromosome were infertile – a genetic dead end. Fernando Mendez of Stanford University, and his colleagues compared the Neanderthal Y chromosome with that of chimps, and ancient and modern humans. They found mutations in four genes that could have prevented the passage of Y chromosome down the paternal line to the hybrid children. “Some of these mutations could have played a role in the loss of Neanderthal Y chromosomes in human populations,” says Mendez. © Copyright Reed Business Information Ltd.
by Daniel Galef Footage from a revolutionary behavioural experiment showed non-primates making and using tools just like humans. In the video, a crow is trying to get food out of a narrow vessel, but its beak is too short for it to reach through the container. Nearby, the researchers placed a straight wire, which the crow bent against a nearby surface into a hook. Then, holding the hook in its beak, it fished the food from the bottle. Corvids—the family of birds that includes crows, ravens, rooks, jackdaws, and jays—are pretty smart overall. Although not to the level of parrots and cockatoos, ravens can also mimic human speech. They also have a highly developed system of communication and are believed to be among the most intelligent non-primate animals in existence. McGill Professor Andrew Reisner recalls meeting a graduate student studying corvid intelligence at Oxford University when these results were first published in 2015. “I had read early in the year that some crows had been observed making tools, and I mentioned this to him,” Reisner explained. “He said that he knew about that, as it had been he who had first observed it happening. Evidently the graduate students took turns watching the ‘bird box,’ […] and the tool making first occurred there on his shift.”
Philip Ball James Frazer’s classic anthropological study The Golden Bough1 contains a harrowing chapter on human sacrifice in rituals of crop fertility and harvest among historical cultures around the world. Frazer describes sacrificial victims being crushed under huge toppling stones, slow-roasted over fires and dismembered alive. Frazer’s methods of analysis wouldn't all pass muster among anthropologists today (his work was first published in 1890), but it is hard not to conclude from his descriptions that what industrialized societies today would regard as the most extreme psychopathy has in the past been seen as normal — and indeed sacred — behaviour. In almost all societies, killing within a tribe or clan has been strongly taboo; exemption is granted only to those with great authority. Anthropologists have suspected that ritual human sacrifice serves to cement power structures — that is, it signifies who sits at the top of the social hierarchy. The idea makes intuitive sense, but until now there has been no clear evidence to support it. In a study published in Nature2, Joseph Watts, a specialist in cultural evolution at the University of Auckland in New Zealand, and his colleagues have analysed 93 traditional cultures in Austronesia (the region that loosely embraces the many small and island states in the Pacific and Indonesia) as they were before they were influenced by colonization and major world religions (generally in the late 19th and early 20th centuries). © 2016 Nature Publishing Group
Ewen Callaway Homo floresiensis, the mysterious and diminutive species found in Indonesia in 2003, is tens of thousands of years older than originally thought — and may have been driven to extinction by modern humans. After researchers discovered H. floresiensis, which they nicknamed the hobbit, in Liang Bua cave on the island of Flores, they concluded that its skeletal remains were as young as 11,000 years old. But later excavations that have dated more rock and sediment around the remains now suggest that hobbits were gone from the cave by 50,000 years ago, according to a study published in Nature on 30 March1. That is around the time that modern humans moved through southeast Asia and Australia. “I can’t believe that it is purely coincidence, based on what else we know happens when modern humans enter a new area,” says Richard Roberts, a geochronologist at the University of Wollongong, Australia. He notes that Neanderthals vanished soon after early modern humans arrived in Europe from Africa. Roberts co-led the study with archaeologist colleague Thomas Sutikna (who also helped coordinate the 2003 dig), and Matthew Tocheri, a paleoanthropologist at Lakehead University in Thunder Bay, Canada. The first hobbit fossil, known as LB1, was found in 20032 beneath about 6 metres of dirt and rock. Its fragile bones were too precious for radiocarbon dating, so the team collected nearby charcoal, on the assumption that it had accrued at the same time as the bones. That charcoal was as young as 11,000 years old, researchers reported at the time3, 4. “Somehow these tiny people had survived on this island 30,000 years after modern humans arrived,” says Roberts. “We were scratching our heads. It couldn’t add up.” © 2016 Nature Publishing Group,
Link ID: 22055 - Posted: 03.31.2016
by Sarah Zielinski There must be something wrong with the guy who never leaves home, right? Maybe not — at least if that guy is a male spotted hyena. Males that stay with their birth clan, instead of taking off to join a new group, may simply be making a good choice, a new study suggests. Spotted hyenas are a matriarchal society. Females are in charge. They rank higher than every male in the clan. And the females generally stay with the clan for their entire lives. But males face a choice when they reach two and a half years in age. They can stay with the clan, or they can leave and join a new clan. Each choice has its pros and cons. Staying with the clan means that a male hyena keeps a place at the top of the male pecking order. He’ll probably have his mother around to help. But he’ll be limited in the number of females he can mate with, because many of the female hyenas won’t mate with him because they might be related. If he joins a new clan, the male hyena might have access to more females — and they might even be better than the ones in his home clan — but he’ll start with the lowest social rank and have to spend years fighting his way to the top. Among most group-living mammal species, the guys that stay at home turn out to be losers, siring fewer offspring. But spotted hyenas, it appears, are an exception. Eve Davidian of the Leibniz Institute for Zoo and Wildlife Research in Berlin and colleagues tracked 254 male spotted hyenas that lived in eight clans in Ngorongoro Crater in Tanzania throughout their lives, a study lasting 20 years. When these males reached the age of maturity, they left their clans to take a look at the other options available to them. Forty-one hyenas returned to their home clans, and 213 settled with new ones. © Society for Science & the Public 2000 - 2016
By Catherine Matacic Twenty-three years ago, a bonobo named Kanzi (above) aced a test in understanding human language. But a new study reveals he may not be as brainy as scientists thought—at least when it comes to grammar. The original test consisted of 660 verbal commands, in English, that asked Kanzi to do things like "show me the hot water" and "pour cold water in the potty." Overall, the ape did well, responding correctly 71.5% of the time (compared with 66.6% for an infant human). But when the researchers asked him to perform an action on more than one item, his performance plummeted to just 22.2%, according to the new analysis. When he was asked to "give the lighter and the shoe to Rose," for example, he gave Rose the lighter, but no shoe. When asked to "give the water and the doggie to Rose," he gave her the toy dog, but no water. The cause? Animals like bonobos may have a harder time than humans in processing complex noun phrases like “water and doggie,” linguist Robert Truswell of the University of Edinburgh reported in New Orleans, Louisiana, this week at the Evolution of Language conference. This feature of grammar—which effectively “nests” one unit within the bigger construct of a sentence—is easily picked up by humans, allowing us to communicate—and understand—more complex ideas. But Truswell cautions that humans probably aren’t born with the ability to interpret this kind of nesting structure. Instead, we must be taught how to use it. © 2016 American Association for the Advancement of Science
By NATALIE ANGIER Juan F. Masello never intended to study wild parrots. Twenty years ago, as a graduate student visiting the northernmost province of Patagonia in Argentina, he planned to write his dissertation on colony formation among seabirds. But when he asked around for flocks of, say, cormorants or storm petrels, a park warden told him he was out of luck. “He said, ‘This is the only part of Patagonia with no seabird colonies,’” recalled Dr. Masello, a principal investigator in animal ecology and systematics at Justus Liebig University in Germany. Might the young scientist be interested in seeing a large colony of parrots instead? The sight that greeted Dr. Masello was “amazing” and “incredible,” he said. “It was almost beyond words.” On a 160-foot-high sandstone cliff that stretched some seven miles along the Atlantic coast, tens of thousands of pairs of burrowing parrots had used their powerful bills to dig holes — their nests — deep into the rock face. And when breeding season began not long afterward, the sky around the cliffs erupted into a raucous carnival of parrot: 150,000 crow-size, polychromed aeronauts with olive backsides, turquoise wings, white epaulets and bright red belly patches ringed in gold. Dr. Masello was hooked. Today, Dr. Masello’s hands are covered with bite scars. He has had four operations to repair a broken knee, a broken nose — “the little accidents you get from working with parrots,” he said. Still, he has no regrets. “Their astonishing beauty and intelligence,” Dr. Masello said, “are inspirational.” © 2016 The New York Times Company
Giant manta rays have been filmed checking out their reflections in a way that suggests they are self-aware. Only a small number of animals, mostly primates, have passed the mirror test, widely used as a tentative test of self-awareness. “This new discovery is incredibly important,” says Marc Bekoff, of the University of Colorado in Boulder. “It shows that we really need to expand the range of animals we study.” But not everyone is convinced that the new study proves conclusively that manta rays, which have the largest brains of any fish, can do this – or indeed, that the mirror test itself is an appropriate measure of self-awareness. Csilla Ari, of the University of South Florida in Tampa, filmed two giant manta rays in a tank, with and without a mirror inside.The fish changed their behaviour in a way that suggested that they recognised the reflections as themselves as opposed to another manta ray. They did not show signs of social interaction with the image, which is what you would expect if they perceived it to be another individual. Instead, the rays repeatedly moved their fins and circled in front of the mirror (click on image below to see one in action). This suggests they could see whether their reflection moved when they moved. The frequency of these movements was much higher when the mirror was in the tank than when it was not. manta © Copyright Reed Business Information Ltd.