Chapter 6. Evolution of the Brain and Behavior
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By Harvey Black The intelligence of the corvid family—a group of birds that includes crows, ravens, magpies, rooks and jackdaws—rivals that of apes and dolphins. Recent studies are revealing impressive details about crows' social reasoning, offering hints about how our own interpersonal intelligence may have evolved. One recent focus has been on how these birds respond to the sight of human faces. For example, crows take to the skies more quickly when an approaching person looks directly at them, as opposed to when an individual nears with an averted gaze, according to a report by biologist Barbara Clucas of Humboldt State University and her colleagues in the April issue of Ethology. The researchers walked toward groups of crows in three locations in the Seattle area, with their eyes either on the birds or on some point in the distance. The crows scattered earlier when the approaching person was looking at them, unlike other animals that avoid people no matter what a person is doing. Clucas speculates that ignoring a human with an averted gaze is a learned adaptation to life in the big city. Indeed, many studies have shown that crows are able to learn safety behaviors from one another. For example, John Marzluff of the University of Washington (who co-authored the aforementioned paper with Clucas) used masked researchers to test the learning abilities of crows. He and his colleagues ventured into Seattle parks wearing one of two kinds of masks. The people wearing one kind of mask trapped birds; the others simply walked by. Five years later the scientists returned to the parks with their masks. The birds present at the original trapping remembered which masks corresponded to capturing—and they passed this information to their young and other crows. All the crows responded to the sight of a researcher wearing a trapping mask by immediately mobbing the individual and shrieking. © 2013 Scientific American
Virginia Morell A wolf’s howl is one of the most iconic sounds of nature, yet biologists aren’t sure why the animals do it. They’re not even sure if wolves howl voluntarily or if it’s some sort of reflex, perhaps caused by stress. Now, scientists working with captive North American timber wolves in Austria report that they’ve solved part of the mystery. Almost 50 years ago, wildlife biologists suggested that a wolf’s howls were a way of reestablishing contact with other pack members after the animals became separated, which often happens during hunts. Yet, observers of captive wolves have also noted that the pattern of howls differs depending on the size of the pack and whether the dominant, breeding wolf is present, suggesting that the canids’ calls are not necessarily automatic responses. Friederike Range, a cognitive ethologist at the University of Veterinary Medicine in Vienna, was in a unique position to explore the conundrum. Since 2008, she and her colleagues have hand-raised nine wolves at the Wolf Science Center in Ernstbrunn, which she co-directs. “We started taking our wolves for walks when they were 6 weeks old, and as soon as we took one out, the others would start to howl,” she says. “So immediately we became interested in why they howl.” Although the center’s wolves don’t hunt, they do howl differently in different situations, Range says. “So we also wanted to understand these variations in their howling.” © 2012 American Association for the Advancement of Science.
By CARL ZIMMER Evolutionary biologists have come to recognize humans as a tremendous evolutionary force. In hospitals, we drive the evolution of resistant bacteria by giving patients antibiotics. In the oceans, we drive the evolution of small-bodied fish by catching the big ones. In a new study, a University of Minnesota biologist, Emilie C. Snell-Rood, offers evidence suggesting we may be driving evolution in a more surprising way. As we alter the places where animals live, we may be fueling the evolution of bigger brains. Dr. Snell-Rood bases her conclusion on a collection of mammal skulls kept at the Bell Museum of Natural History at the University of Minnesota. Dr. Snell-Rood picked out 10 species to study, including mice, shrews, bats and gophers. She selected dozens of individual skulls that were collected as far back as a century ago. An undergraduate student named Naomi Wick measured the dimensions of the skulls, making it possible to estimate the size of their brains. Two important results emerged from their research. In two species — the white-footed mouse and the meadow vole — the brains of animals from cities or suburbs were about 6 percent bigger than the brains of animals collected from farms or other rural areas. Dr. Snell-Rood concludes that when these species moved to cities and towns, their brains became significantly bigger. Dr. Snell-Rood and Ms. Wick also found that in rural parts of Minnesota, two species of shrews and two species of bats experienced an increase in brain size as well. Dr. Snell-Rood proposes that the brains of all six species have gotten bigger because humans have radically changed Minnesota. Where there were once pristine forests and prairies, there are now cities and farms. In this disrupted environment, animals that were better at learning new things were more likely to survive and have offspring. © 2013 The New York Times Company
By Jessica Shugart Sometimes it pays to be mediocre. A new study shows that sheep with a 50/50 blend of genes for small and big horns pass along more of their genes over a lifetime than their purely big-horned brethren, who mate more often. The finding offers rare insight into an enduring evolutionary paradox—why some traits persist despite creating a reproductive disadvantage. The results, published online August 21 in Nature, reveal that while big-horned sheep mated most successfully each season, small-horned sheep survived longer. Rams who inherited one of each type of gene from their parents got the best of both worlds: they lived longer than bigger-horned sheep and mated more successfully than those with the smallest horns. As a result, middle-of-the-road sheep passed on more of their genes over time. “They’re the fittest of them all,” says Jon Slate of the University of Sheffield in Scotland, who led the study. “This is a marvelous combination of using the most modern tools available to confirm classic older views of sexual selection,” says evolutionary geneticist Allen Moore of the University of Georgia in Athens, who was not involved in the study. Traits such as bold peacock feathers and giant antlers evolved to garner the attention of prospective females and boost reproductive success. Yet if each generation of females continues to pick the most stellar males, Charles Darwin wondered, how do sub-par versions of a trait continue to persist? “It’s something that has preoccupied evolutionary biologists ever since,” Slate says. © Society for Science & the Public 2000 - 2013
by Ed Yong In the image above, all the eggs in the top row are laid by cuckoos and those in the bottom row belong to their victims. These uncanny similarities help cuckoos to fob off their parental duties by laying their eggs in the nests of other species. If the hosts can’t tell the difference between their eggs and the foreign ones, they’ll end up raising the cuckoo chick as their own. And they pay a hefty price for their gullibility, since cuckoo chicks often kill or outcompete their foster siblings. The relationship between cuckoos and their hosts is a classic example of an evolutionary arms race. Cuckoos, should evolve eggs that more closely match those of their hosts, while the hosts should evolve keener senses to discriminate between their own eggs and a cuckoo’s. The greater honeyguide isn’t a cuckoo but uses the same tactics—it parasitises the nests of little bee-eaters by laying eggs of the same size and shape. But this mimicry doesn’t help it to fool the bee-eaters, which seem to accept any old egg no matter how different it looks. Instead, Claire Spottiswoode from the University of Cambridge has found that the parasitic honeyguides are fighting an evolutionary arms race against… each other. Bee-eaters build their nests underground, usually within abandoned aardvark burrows. When honeyguides invade, they’ll puncture the bee-eater’s eggs before laying their own. This kills some of the eggs outright and weakens others. If any chicks survive to hatching, they’re finished off by the honeyguide chick, which stabs its foster siblings to death with a vicious hooked bill.
Louis Herman The mournful, curiously repetitious yet ever-changing songs of male humpback whales have long puzzled scientists. The tunes are part of the males’ mating displays, but researchers don’t know their exact function, or which males in a population are doing the singing. Now, scientists who’ve been studying the giant marine mammals in Hawaii for almost 40 years report that even sexually immature males join older males in singing, apparently as a way to learn the music and to amplify the song. The beefed-up, all-male choruses may attract more females to the areas where the songsters hang out. Scientists generally thought that only adult male humpbacks (Megaptera novaeangliae) sing, says Louis Herman, a marine mammal biologist emeritus at the University of Hawaii, Manoa, and the lead author of the new study. “But that’s just because you can’t easily tell which ones are mature and which ones are immature,” he says. “We know that mature males are larger than immature ones, so we had to figure out an unobtrusive way to measure them in the open ocean.” Herman and his team hit on a technique by looking at 20th century whaling records. Biologists with whaling operations in the Southern Ocean had the opportunity to measure many humpbacks killed during the commercial hunts. They determined, based on the weight of males’ testes, that the whales reached sexual maturity at a body length of 11.2 meters. Working independently, whaling biologists in Japan, who also measured killed whales, reached a similar conclusion; they described 11.3 meters as the break point between adolescents and adults. © 2012 American Association for the Advancement of Science
Karen Ravn The authors of a new study write that this plant bug, Coridromius tahitiensis, “lacks precopulatory courtship, and males instead pounce on nearby females, with whom they struggle violently in their attempt to mate.” If you lived on an exotic island where unsafe sex was all too common, you'd find ways to ward off unwanted attention. On Tahiti, the females of two related insect species have had to move their genitals to different sides of their bodies and even impersonate the opposite sex — all to avoid getting pierced in the abdomen by the sexual organs of the wrong males, biologists report. The two insects, which live side by side on the Pacific island of Tahiti and feed on the same plants, are known as Coridromius tahitiensis and Coridromius taravao. Both species follow the aptly named practice of traumatic insemination. With his genital organ reminiscent of a hypodermic needle, the male stabs a female in the side and shoots sperm into her abdomen. The ritual — shared by a number of other invertebrates, including bedbugs (Cimex lectularius) — can cause injury or infection for the female. Not only that, but insects that use this type of reproductive method are not particularly persnickety about partners, so a male of one species may try to mate with another male — or even with a member of another species. Such interspecies mating can be costly to both species in terms of wasted time, energy and sperm, says Nikolai Tatarnic, a biologist who is now curator of insects at the Western Australian Museum in Welshpool. © 2013 Nature Publishing Group,
by Laura Poppick, LiveScience Researchers have widely examined homosexual behavior in mammals and birds, but have addressed it less frequently in insects and spiders. To assess the range of evolutionary explanations for same-sex intercourse in the invertebrate world, a team of biologists from Tel Aviv University in Israel and the Swiss Federal Institute of Technology in Zurich, Switzerland examined roughly 100 existing studies on the topic and compiled the first comprehensive review of homosexuality in invertebrates. The review was published earlier this month in the journal Behavioral Ecology and Sociobiology. The team focused on male-male interactions to simplify the analysis, and found that most of these encounters occurred as accidents. Whereas larger animals have developed more complicated homosexual motivations — like maintaining alliances, which has been found in certain primate and seagull species — insects seem to mistakenly partake in it in a hasty attempt to secure mates. [Gay Animals: Alternate Lifestyles in the Wild] "They have evolved to mate quick and dirty," said study co-author Inon Scharf, an evolutionary ecologist at Tel Aviv University. "They grab every opportunity to mate that they have because, if they become slow, they may give up an opportunity to mate." In some cases, males carry around the scent of females they have just mated with, sending confusing signals to other perusing males. In other cases, males and females look so similar to one another that males cannot tell if a potential mate is a female until he mounts "her" and prepares for the act, Scharf said. © 2013 Discovery Communications, LLC.
// by Jennifer Viegas Single parenting takes on new extremes for certain starfish that are hermaphrodites -- male and female at the same time and, in some cases, self-fertilizing. The species faces high risk of extinction, according to new research. The dire situation faced by the non-mating starfish, Parvulastra parvivipara and Parvulastra vivipara, helps to explain why so many organisms, including humans, have sex. Genetic diversity and the dispersal of youngsters support population growth. The plight of the starfish, documented in the latest issue of the journal Biology Letters, reveals how a life without sex but with self-fertilization could result in eventual oblivion. “There are quite a few reasons why these species are vulnerable,” senior author Michael Hart of Simon Fraser University’s Department of Biological Sciences told Discovery News. “The whole species could be wiped out.” Hart and his team studied the starfish, which are restricted to high intertidal pools of South Australia and Tasmania. These starfish also go by the nickname "sea cushions," since they look a bit more like a cushion than a star when viewed from the side. Most adult starfish of other species do reproduce via a separate male and female. Females usually produce eggs that males fertilize in the seawater. At that point, the fertilized eggs develop and grow before becoming little starfish that will attach themselves to the substrate and start the whole process over again. © 2013 Discovery Communications, LLC.
By CARL ZIMMER “Monogamy is a problem,” said Dieter Lukas of the University of Cambridge in a telephone news conference this week. As Dr. Lukas explained to reporters, he and other biologists consider monogamy an evolutionary puzzle. In 9 percent of all mammal species, males and females will share a common territory for more than one breeding season, and in some cases bond for life. This is a problem — a scientific one — because male mammals could theoretically have more offspring by giving up on monogamy and mating with lots of females. In a new study, Dr. Lukas and his colleague Tim Clutton-Brock suggest that monogamy evolves when females spread out, making it hard for a male to travel around and fend off competing males. On the same day, Kit Opie of University College London and his colleagues published a similar study on primates, which are especially monogamous — males and females bond in over a quarter of primate species. The London scientists came to a different conclusion: that the threat of infanticide leads males to stick with only one female, protecting her from other males. Even with the scientific problem far from resolved, research like this inevitably turns us into narcissists. It’s all well and good to understand why the gray-handed night monkey became monogamous. But we want to know: What does this say about men and women? As with all things concerning the human heart, it’s complicated. © 2013 The New York Times Company
By Melissa Hogenboom Science reporter, BBC News Several ancient dinosaurs evolved the brainpower needed for flight long before they could take to the skies, scientists say. Non-avian dinosaurs were found to have "bird brains", larger than that of Archaeopteryx, a 150 million-year-old bird-like dinosaur. Once regarded as a unique transition between dinosaurs and birds, scientists say Archaeopteryx has now lost its pivotal place. The study is published in Nature. A recent discovery in China which unveiled the earliest creature yet discovered on the evolutionary line to birds, also placed Archaeopteryx in less of a transitional evolutionary place. Bird brains tend to be more enlarged compared to their body size than reptiles, vital for providing the vision and coordination needed for flight. Scientists using high-resolution CT scans have now found that these "hyper-inflated" brains were present in many ancient dinosaurs, and had the neurological hardwiring needed to take to the skies. This included several bird-like oviraptorosaurs and the troodontids Zanabazar junior, which had larger brains relative to body size than that of Archaeopteryx. This latest work adds to previous studies which found the presence of feathers and wishbones on ancient dinosaurs. BBC © 2013
Link ID: 18439 - Posted: 08.01.2013
Andrew Curry In the 1970s, archaeologist Peter Bogucki was excavating a Stone Age site in the fertile plains of central Poland when he came across an assortment of odd artefacts. The people who had lived there around 7,000 years ago were among central Europe's first farmers, and they had left behind fragments of pottery dotted with tiny holes. It looked as though the coarse red clay had been baked while pierced with pieces of straw. Looking back through the archaeological literature, Bogucki found other examples of ancient perforated pottery. “They were so unusual — people would almost always include them in publications,” says Bogucki, now at Princeton University in New Jersey. He had seen something similar at a friend's house that was used for straining cheese, so he speculated that the pottery might be connected with cheese-making. But he had no way to test his idea. The mystery potsherds sat in storage until 2011, when Mélanie Roffet-Salque pulled them out and analysed fatty residues preserved in the clay. Roffet-Salque, a geochemist at the University of Bristol, UK, found signatures of abundant milk fats — evidence that the early farmers had used the pottery as sieves to separate fatty milk solids from liquid whey. That makes the Polish relics the oldest known evidence of cheese-making in the world1. © 2013 Nature Publishing Group
By CARL ZIMMER The golden lion tamarin, a one-pound primate that lives in Brazil, is a stunningly monogamous creature. A male will typically pair with a female and they will stay close for the rest of their lives, mating only with each other and then working together to care for their young. To biologists, this deeply monogamous way of life — found in 9 percent of mammal species — is puzzling. A seemingly better evolutionary strategy for male mammals would be to spend their time looking for other females with which to mate. “Monogamy is a problem,” said Dieter Lukas of the University of Cambridge in a telephone news conference on Monday. “Why should the male keep to one female?” The evolution of monogamy has inspired many different ideas. “These hypotheses have been suggested for the past 40 years, and there’s been no resolution of the debate,” said Kit Opie of the University College London in an interview. On Monday, Dr. Opie and Dr. Lukas each published a large-scale study of monogamy that they hoped would resolve the debate. But they ended up coming to opposing conclusions, which means the debate over monogamy continues. Dr. Lukas, co-author of a paper in the journal Science with Tim Clutton-Brock of Cambridge, looked at 2,545 species of mammals, tracing their mating evolution from their common ancestor some 170 million years ago. The scientists found that mammals shifted from solitary living to monogamy 61 times over their evolution. They then searched for any factors that these mammals had in common. They concluded that monogamy evolves when females become hostile with one another and live in ranges that do not overlap. When females live this way, they set up so much distance between one another that a single male cannot prevent other males from mating with them. Staying close to one female became a better strategy. Once males began doing so, they sometimes evolved to provide care to their offspring as well. © 2013 The New York Times Company
By JAMES GORMAN Should some of the most social, intelligent and charismatic animals on the planet be kept in captivity by human beings? That is a question asked more frequently than ever by both scientists and animal welfare advocates, sometimes about close human cousins like chimpanzees and other great apes, but also about another animal that is remarkable for its intelligence and complex social organization — the killer whale, or orca. Killer whales, found in all the world’s oceans, were once as despised as wolves. But in the last half century these elegant black-and-white predators — a threat to seals and other prey as they cruise the oceans, but often friendly to humans in the wild — have joined the pantheon of adored wildlife, along with the familiar polar bears, elephants and lions. With life spans that approach those of humans, orcas have strong family bonds, elaborate vocal communication and cooperative hunting strategies. And their beauty and power, combined with a willingness to work with humans, have made them legendary performers at marine parks since they were first captured and exhibited in the 1960s. They are no longer taken from the wild as young to be raised and trained, but are bred in captivity in the United States for public display at marine parks. Some scientists and activists have argued for years against keeping them in artificial enclosures and training them for exhibition. They argue for more natural settings, like enclosed sea pens, as well as an end to captive breeding and to the orcas’ use in what opponents call entertainment and marine parks call education. Now the issue has been raised with new intensity in the documentary film “Blackfish” and the book “Death at SeaWorld,” by David Kirby, just released in paperback. © 2013 The New York Times Company
John Hawks Humans are known for sporting big brains. On average, the size of primates' brains is nearly double what is expected for mammals of the same body size. Across nearly seven million years, the human brain has tripled in size, with most of this growth occurring in the past two million years. Determining brain changes over time is tricky. We have no ancient brains to weigh on a scale. We can, however, measure the inside of ancient skulls, and a few rare fossils have preserved natural casts of the interior of skulls. Both approaches to looking at early skulls give us evidence about the volumes of ancient brains and some details about the relative sizes of major cerebral areas. For the first two thirds of our history, the size of our ancestors' brains was within the range of those of other apes living today. The species of the famous Lucy fossil, Australopithecus afarensis, had skulls with internal volumes of between 400 and 550 milliliters, whereas chimpanzee skulls hold around 400 ml and gorillas between 500 and 700 ml. During this time, Australopithecine brains started to show subtle changes in structure and shape as compared with apes. For instance, the neocortex had begun to expand, reorganizing its functions away from visual processing toward other regions of the brain. The final third of our evolution saw nearly all the action in brain size. Homo habilis, the first of our genus Homo who appeared 1.9 million years ago, saw a modest hop in brain size, including an expansion of a language-connected part of the frontal lobe called Broca's area. The first fossil skulls of Homo erectus, 1.8 million years ago, had brains averaging a bit larger than 600 ml. © 2013 Scientific American
By DAVID CRARY, AP National Writer NEW YORK (AP) — There's extensive evidence that pigs are as smart and sociable as dogs. Yet one species is afforded affection and respect; the other faces mass slaughter en route to becoming bacon, ham and pork chops. Seeking to capitalize on that discrepancy, animal-welfare advocates are launching a campaign called The Someone Project that aims to highlight research depicting pigs, chickens, cows and other farm animals as more intelligent and emotionally complex than commonly believed. The hope is that more people might view these animals with the same empathy that they view dogs, cats, elephants, great apes and dolphins. "When you ask people why they eat chickens but not cats, the only thing they can come up with is that they sense cats and dogs are more cognitively sophisticated that then species we eat — and we know this isn't true," said Bruce Friedrich of Farm Sanctuary, the animal-protection and vegan-advocacy organization that is coordinating the new project. "What it boils down to is people don't know farm animals the way they know dogs or cats," Friedrich said. "We're a nation of animal lovers, and yet the animals we encounter most frequently are the animals we pay people to kill so we can eat them." The lead scientist for the project is Lori Marino, a lecturer in psychology at Emory University who has conducted extensive research on the intelligence of whales, dolphins and primates. She plans to review existing scientific literature on farm animals' intelligence, identify areas warranting new research, and prepare reports on her findings that would be circulated worldwide via social media, videos and her personal attendance at scientific conferences. © 2013 Hearst Communications Inc.
By Michelle Warwicker BBC Nature Individual wild wolves can be recognised by just their howls with 100% accuracy, a study has shown. The team from Nottingham Trent University, UK, developed a computer program to analyse the vocal signatures of eastern grey wolves. Wolves roam huge home ranges, making it difficult for conservationists to track them visually. But the technology could provide a way for experts to monitor individual wolves by sound alone. "Wolves howl a lot in the wild," said PhD student Holly Root-Gutteridge, who led the research. "Now we can be sure... exactly which wolf it is that's howling." The team's findings are published in the journal Bioacoustics. Wolves use their distinctive calls to protect territory from rivals and to call to other pack members. "They enjoy it as a group activity," said Ms Root-Gutteridge, "When you get a chorus howl going they all join in." The team's computer program is unique because it analyses both volume (or amplitude) and pitch (or frequency) of wolf howls, whereas previously scientists had only examined the animals' pitch. "Think of [pitch] as the note the wolf is singing," explained Ms Root-Gutteridge. "What we've added now is the amplitude - or volume - which is basically how loud it's singing at different times." "It's a bit like language: If you put the stress in different places you form a different sound." BBC © 2013
By Rebecca Morelle Science reporter, BBC World Service Scientists have found further evidence that dolphins call each other by "name". Research has revealed that the marine mammals use a unique whistle to identify each other. A team from the University of St Andrews in Scotland found that when the animals hear their own call played back to them, they respond. The study is published in the Proceedings of the National Academy of Sciences. Dr Vincent Janik, from the university's Sea Mammal Research Unit, said: "(Dolphins) live in this three-dimensional environment, offshore without any kind of landmarks and they need to stay together as a group. "These animals live in an environment where they need a very efficient system to stay in touch." It had been-long suspected that dolphins use distinctive whistles in much the same way that humans use names. Previous research found that these calls were used frequently, and dolphins in the same groups were able to learn and copy the unusual sounds. But this is the first time that the animals response to being addressed by their "name" has been studied. To investigate, researchers recorded a group of wild bottlenose dolphins, capturing each animal's signature sound. BBC © 2013
by Virginia Morell The next time your dog digs a hole in the backyard after watching you garden, don't punish him. He's just imitating you. A new study reveals that our canine pals are capable of copying our behavior as long as 10 minutes after it's happened. The ability is considered mentally demanding and, until this discovery, something that only humans and apes were known to do. Scientists first discovered that dogs are excellent at imitating their owners in 2006. Or at least, one dog had the talent: Philip, a 4-year-old Belgian Tervuren working with József Topál, a behavioral ethologist at the Hungarian Academy of Sciences in Budapest. Topál adapted the method (called "Do as I do") that Keith and Catherine Hayes developed in the 1950s for teaching an infant chimpanzee to copy their actions. Philip was already a trained assistant dog for his disabled owner and readily followed Topál's commands. First, Topál told him to stay, and then commanded "Do as I do." The researcher then performed a simple action, such as jumping in place, barking, putting an object in a box, or carrying it to Philip's owner. Next, Topál ordered, "Do it!", and Philip responded by matching the scientist's actions. The experiment was designed to explore dog's imitative abilities, not to measure how long Philip's memory lasted; but his owner used Philip's skill to teach him how to do new, useful behaviors, such as fetching objects or putting things away. Despite Philip's abilities, "nobody really cared, or saw that it could be useful for investigating how dogs learn or see their world," says Ádám Miklósi, a behavioral ethologist at Eötvös Loránd University in Budapest who was part of Topál's team. And in 2009, another team concluded that dogs were only able to correctly imitate if there was no more than a 5-second delay between watching the action and repeating it. With such a short retention span, dogs' vaunted imitation skills seemed useless. © 2010 American Association for the Advancement of Science
by Virginia Morell A single cue—the taste of a madeleine, a small cake, dipped in lime tea—was all Marcel Proust needed to be transported down memory lane. He had what scientists term an autobiographical memory of the events, a type of memory that many researchers consider unique to humans. Now, a new study argues that at least two species of great apes, chimpanzees and orangutans, have a similar ability; in zoo experiments, the animals drew on 3-year-old memories to solve a problem. Their findings are the first report of such a long-lasting memory in nonhuman animals. The work supports the idea that autobiographical memory may have evolved as a problem-solving aid, but researchers caution that the type of memory system the apes used remains an open question. Elephants can remember, they say, but many scientists think that animals have a very different kind of memory than our own. Many can recall details about their environment and routes they've traveled. But having explicit autobiographical memories of things "I" did, or remembering events that occurred in the past, or imagining those in the future—so-called mental time travel—are considered by many psychologists to be uniquely human skills. Until recently, scientists argued that animals are stuck in time, meaning that they have no sense of the past or future and that they aren't able to recall specific events from their lives—that is, they don't have episodic memories, the what-where-when of an event that happened. © 2010 American Association for the Advancement of Science