Chapter 6. Evolution of the Brain and Behavior
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By Jason G. Goldman Scientists love yawning. No, that’s not quite right. Scientists love doing research on yawning. It seems to be of interest to folks in fields ranging from primatology to developmental psychology to psychopathology to animal behavior. If the notion of scientifically investigation the purpose of yawning makes you, well, yawn, then you’re missing one of the more interesting debates in the social cognition literature. To understand why yawning is about more than feeling tired or bored, we have to go back a few years. Once upon a time, scientists thought that yawning might be process through which the brain keeps itself cool (PDF). Yawning is associated with increases in blood pressure, and the consequential increase in blood flow might mean that the vascular system acts as a radiator, replacing the warm blood in the brain with cooler blood. It could also be that the deep inhalation of cold air during a yawn can, through convection, alter blood temperature which in turn could cool the brain. Even if it turns out that some yawns can be explained through purely physiological means, yawning is also contagious for humans and other species. If someone watches someone else yawning, they’ll be likely to yawn as well. That means that there is social component to yawning, and it might be related to empathy. It turns out that there’s a correlation between a person’s self-reported empathy and their susceptibility to reacting to a yawn contagion, and those who are more skilled at theory of mind tasks are also more likely (PDF) to yawn contagiously. © 2013 Scientific American
by Stephanie Pappas, LiveScience Apes orphaned by the African bushmeat trade lack the social savvy of apes raised by their mothers, a new study finds. The study links the emotional development of bonobos (Pan paniscus), one of humans' closest living relatives, with the ability to interact nicely with others, echoing how human emotions develop. Bonobos who are good at soothing themselves out of a bad mood are more likely to comfort other bonobos in distress, researchers report today (Oct. 14) in the journal Proceedings of the National Academy of Sciences. "By measuring the expression of distress and arousal in great apes, and how they cope, we were able to confirm that efficient emotion regulation is an essential part of empathy," study researcher Frans de Waal, of Emory University's National Primate Research Center, said in a statement. PHOTOS: How Santino, the Chimp, Attacks Visitors Though animal emotions "have long been scientifically taboo," de Waal said, he and his colleagues suspected that emotions might have evolved similarly before the bonobo and human lines split about 6 million years ago. The researchers observed juvenile bonobos at a sanctuary near Kinshasa in the Democratic Republic of the Congo. They watched as the young primates fought, threw tantrums and comforted one another by hugging or stroking. (See Video of a Bonobo Hug) In 373 post-distress interactions (318 caused by fights and 55 caused by tantrums), the researchers found that the better a bonobo was at soothing his or her own emotions, the more likely he or she was to rush to aid a friend in need. A similar pattern is seen in human interactions, the researchers reported. © 2013 Discovery Communications, LLC.
by Jack Flanagan Although dogs are said to be man's best friend, it doesn't mean they "get" us. At least, not like elephants seem to. Without any training, the giant herbivores can understand and follow our hand gestures – the first non-human animals known to be able to do so. Elephants have lived alongside humans for between 4000 and 8000 years. Despite their potential to be tamed, though, elephants have never been domesticated in the same way as dogs, cats and agricultural animals have. This hasn't prevented them from developing a number of human-like skills. In the wild, they are famously empathetic towards one another. In captivity, elephants have displayed a degree of self-awareness by being able to recognise themselves in a mirrorMovie Camera. Others have developed the teamwork necessary to coordinate and complete a task. In fact, one elephant has even learned some basic phrases in Korean – and another has been taught to paint by its parents. Arguably it was only a matter of time before they added another skill to their impressive repertoire. Hidden talent Pointing gestures are common enough among humans: from an early age babies naturally recognise the meaning behind them. We know that chimpanzees and even seals can do this too, but not without hours of training. It comes as a surprise, then, to discover that elephants can find hidden food once it is pointed out to them – without any prior lessons. © Copyright Reed Business Information Ltd.
by Erika Engelhaupt Could I interest you in eating the partially digested stomach contents of a porcupine? No? Maybe a spot of reindeer stomach, then. Still no? Well, that’s curious. The Western aversion to these dishes is odd, because people around the world have long partaken of — even delighted in — the delicacy known to medical science as chyme. That’s what becomes of food after it’s chewed, swallowed and mushed around in the stomach for a while with a healthy dose of hydrochloric acid. And, researchers now suggest, Neandertals were no exception. Eating chyme may even explain the presence of some puzzling plant matter found in Neandertal’s tartar-crusted teeth. Neandertals didn’t have great dental care, and in the last few years anthropologists have begun to take advantage of monstrous tartar buildup on fossilized teeth to figure out what the hominids ate. Various chemical signatures, starch grains and even tiny plant fossils called phytoliths get preserved in the tartar, also known as calculus. Just what Neandertals ate has been more of a puzzle than paleo dieters might have you believe. Isotope analyses of fossilized bones and teeth suggest Neandertals ate very high on the food chain, with high-protein diets akin to those of wolves or hyenas. But wear marks on their teeth suggest the Neandertal diet consisted of more animals in colder high-latitude areas, and more of a mix of plants and animals in warmer areas. Tartar analyses support the idea that Neandertals ate their veggies, and have also suggested the presence of plants considered inedible, or at least unpalatable and non-nutritious. These include some plants like yarrow and chamomile with medicinal value, so one team suggested Neandertals self-medicated. © Society for Science & the Public 2000 - 2013
Link ID: 18776 - Posted: 10.12.2013
By Justin Gregg Santino was a misanthrope with a habit of pelting tourists with rocks. As his reputation for mischief grew, he had to devise increasingly clever ways to ambush his wary victims. Santino learned to stash his rocks just out of sight and casually stand just a few feet from them in order to throw off suspicion. At the very moment that passersby were fooled into thinking that he meant them no harm, he grabbed his hidden projectiles and launched his attack. Santino was displaying an ability to learn from his past experiences and plan for future scenarios. This has long been a hallmark of human intelligence. But a recently published review paper by the psychologist Thomas Zentall from the University of Kentucky argues that this complex ability should no longer be considered unique to humans. Santino, you see, is not human. He’s a chimpanzee at Furuvik Zoo in Sweden. His crafty stone-throwing escapades have made him a global celebrity, and also caught the attention of researchers studying how animals, much like humans, might be able to plan their behavior. Santino is one of a handful of animals that scientists believe are showing a complex cognitive ability called episodic memory. Episodic memory is the ability to recall past events that one has the sense of having personally experienced. Unlike semantic memory, which involves recalling simple facts like “bee stings hurt,” episodic memory involves putting yourself at the heart of the memory; like remembering the time you swatted at a bee with a rolled up newspaper and it got angry and stung your hand. © 2013 Scientific American
By DAVID P. BARASH WAR is in the air. Sad to say, there’s nothing new about this. Nor is there anything new about the claim that war has always been with us, and always will be. What is new, it seems, is the degree to which this claim is wrapped in the apparent acquiescence of science, especially the findings of evolutionary biology with respect to a war-prone “human nature.” This year, an article in The National Interest titled “What Our Primate Relatives Say About War” answered the question “Why war?” with “Because we are human.” In recent years, a piece in New Scientist asserted that warfare has “played an integral part in our evolution” and an article in the journal Science claimed that “death in warfare is so common in hunter-gatherer societies that it was an important evolutionary pressure on early Homo sapiens.” The emerging popular consensus about our biological predisposition to warfare is troubling. It is not just scientifically weak; it is also morally unfortunate, as it fosters an unjustifiably limited vision of human potential. Although there is considerable reason to think that at least some of our hominin ancestors engaged in warlike activities, there is also comparable evidence that others did not. While it is plausible that Homo sapiens owed much of its rapid brain evolution to natural selection’s favoring individuals that were smart enough to defeat their human rivals in violent competition, it is also plausible that we became highly intelligent because selection favored those of our ancestors who were especially adroit at communicating and cooperating. Conflict avoidance, reconciliation and cooperative problem solving could also have been altogether “biological” and positively selected for. © 2013 The New York Times Company
At Pimlico Race Course in Baltimore every May, the winning horse in the Preakness Stakes is draped with a blanket covered with what appear to be the Maryland state flower, the black-eyed Susan. But the flower doesn't bloom until later in the season. Those crafting the victory blanket must resort to using yellow Viking daisies — and painting the centers black. That might fool race fans, but bees can see through the ruse. With eyes equipped to detect ultraviolet light, a bee can pick out an additional band in the black-eyed Susan's bull's-eye. The insect's livelihood depends on it. At the center of the target is the flower's nutritional payload, nectar and pollen, which also glows in UV light. As with other members of the sunflower family, black-eyed Susan flower heads are composed of two kinds of florets. The dark center is made up of numerous disc florets, each of which contains male and female reproductive components. When a bee or other pollinator fertilizes a disc floret, it develops a single seed that ripens and falls from the flower head in the autumn. Seeds can remain viable for more than 30 years. Circling the disc florets are bright yellow ray florets, which flag down pollinators and act as landing strips. The inner portion of each ray floret contains several compounds that absorb UV rays. The outer portion reflects UV rays, contributing a visually energetic outer ring to the pattern — provided you're a bee. Black-eyed Susan, Rudbeckia hirta. © 1996-2013 The Washington Post
By Felicity Muth In most animals, females are generally the ones that choose the males. This is a massive generalisation (for example, it doesn’t apply in this case), but I hope people who work on this topic will forgive me for it. Generally speaking, it’s the females that get to size up the males, check out whatever trait it is that’s attractive to them (be it weight, head feather colour, ability to sing, or muscle size) and then choose who they want to mate with. However, how animals (even insects) behave when choosing mates is by no means governed by fixed rules, and is influenced by many different things. I’ve previously written about fish that will change how they court females depending on who’s watching and male crickets that will change their victory displays after fighting with another male depending on their audience. Similarly, what a female chooses in a male mate isn’t totally free from influences outside the quality of the male in question. In some species, such as the field cricket, wolf spider and cowbirds, females with more experience choose differently to naïve females. But what other things might affect what females choose? Pretty much all animals come into contact and may be infected by parasites at some point in their life. Amazingly, parasites seem to affect the mating behaviour of animals in some unusual and unexpected ways. Some parasites castrate their hosts, or change who the host wants to mate with. Others can even cause sex-role reversals, such as in the bush cricket. © 2013 Scientific American
// by Jennifer Viegas Certain animals may weep out of sorrow, similar to human baby cries, say animal behavior experts. Many may have wondered if this was true after news reports last week described a newborn elephant calf at Shendiaoshan Wild Animal Nature Reserve in eastern China. The calf reportedly cried inconsolably for five hours after being stomped on by his mother that then rejected the little elephant. The calf, named Zhuang-zhuang, has since been "adopted" by a keeper and is doing well, according to the news site Metro. "Some mammals may cry due to loss of contact comfort," animal behaviorist Marc Bekoff explained to Discovery News. An ape's laugh is similar to a human one, according to new research exploring the evolution of laughter. "It could be a hard-wired response to not feeling touch," added Bekoff, former professor of ecology and evolutionary biology at the University of Colorado, Boulder. © 2013 Discovery Communications, LLC.
Associated Press It's the ape equivalent of Google Maps and Facebook. The night before a big trip, Arno the orangutan plots his journey and lets others know where he is going with a long, whooping call. What he and his orangutan buddies do in the forests of Sumatra tells scientists that advance trip planning and social networking aren't just human traits. A new study of 15 wild male orangutans finds that they routinely plot out their next-day treks and share their plans in long calls, so females can come by or track them, and competitive males can steer clear. The researchers closely followed the males as they traveled on 320 days during the 1990s. The results were published Wednesday in the journal PLoS One. Typically, an orangutan would turn and face in the direction of his route and let out a whoop, sometimes for as long as four minutes. Then he'd go to sleep and 12 hours later set on the heralded path, said study author Carel van Schaik, director of the Anthropological Institute at the University of Zurich. "This guy basically thinks ahead," van Schaik said. "They're continuously updating their Google Maps, so to speak. Based on that, they're planning what to do next." The apes didn't just call once - they kept at it, calling more than 1,100 times over the 320 days. © 2013 The Hearst Corporation
By Susan Milius Mice in the wild have no problem dining where someone else has pooped. Animals with higher standards of hygiene, reported in earlier studies, may not face the same dangers as small, hungry creatures scurrying around the woods. Feeding among feces of your own species raises the risk of catching nasty intestinal parasites, explains behavioral ecologist Patrick T. Walsh of University of Edinburgh. So far most tests of fecal avoidance have focused on hoofed animals. Horses, cows, sheep, reindeer and even wild antelopes tend not to graze in heavily poop-dotted areas. White-footed and deer mice, however, show no such daintiness of manners in a test in the woods, Walsh and his colleagues report in the September Animal Behaviour. Wild mice may have more immediate problems, like starvation or predators that domesticated--or just plain bigger--animals don’t. For the wild mice, Walsh says, fecal avoidance may be “a luxury.” Learning whether and when animals avoid poop helps clarify how parasites spread, an issue important for the health of both wildlife and people. So far no one has tested fecal avoidance for mice feeding in the lab, but research has shown that female lab mice tend to avoid the urine of parasite-infected males. To see whether mice in the wild dodge parasite risks, Amy Pedersen, a coauthor of the study also at Edinburgh, designed an experiment with a long plastic box divided into zones, some of which had mouse droppings in them. In the experiment, researchers tested more than 130 wild Peromyscus mice, of either the leucopus or maniculatus species, held captive for less than a day in the mountains of Virginia. © Society for Science & the Public 2000 - 2013
Bird species with larger than average brains have lower levels of a key stress hormone, an analysis of nearly 200 avian studies has concluded. Such birds keep their stress down by anticipating or learning to avoid problems more effectively than smaller-brained counterparts, researchers suggest. Birds in the wild lead a stressful life. Constantly spotting predators lurking in the trees or sensing dramatic changes in temperature is essential for survival, but can leave birds on the edge of a nervous breakdown. Reading these cues triggers changes in the birds’ metabolism, particularly increases in the stress hormone corticosterone. A sharp release of the hormone within 1 to 2 minutes after a cue triggers an emergency response and prepares birds to react quickly to the threat. However, regular exposure to the dangers of the wild and, hence, to high levels of this hormone, has serious health consequences and shortens life expectancy. Not all birds respond to stress in the same way, however, notes Daniel Sol an ornithologist at the Centre for Ecological Research and Forestry Applications in Cerdanyola del Vallès, Spain. He and colleagues have for years looked at the differences between big-brained birds, such as crows and parrots, and those with smaller brains, such as chickens and quails. The former survive better in nature and are also more successful at establishing a community in a new environment. In their new work, they connect brain size to handling stress. Sol; Ádám Lendvai, an evolutionary biologist at the College of Nyíregyháza in Hungary; and colleagues scoured the avian research literature to find studies that had measured corticosterone levels in birds in varying situations. © 2012 American Association for the Advancement of Science
Elizabeth Pennisi Dolphins and bats don't have much in common, but they share a superpower: Both hunt their prey by emitting high-pitched sounds and listening for the echoes. Now, a study shows that this ability arose independently in each group of mammals from the same genetic mutations. The work suggests that evolution sometimes arrives at new traits through the same sequence of steps, even in very different animals. The research also implies that this convergent evolution is common—and hidden—within genomes, potentially complicating the task of deciphering some evolutionary relationships between organisms. Nature is full of examples of convergent evolution, wherein very distantly related organisms wind up looking alike or having similar skills and traits: Birds, bats, and insects all have wings, for example. Biologists have assumed that these novelties were devised, on a genetic level, in fundamentally different ways. That was also the case for two kinds of bats and toothed whales, a group that includes dolphins and certain whales, that have converged on a specialized hunting strategy called echolocation. Until recently, biologists had thought that different genes drove each instance of echolocation and that the relevant proteins could change in innumerable ways to take on new functions. But in 2010, Stephen Rossiter, an evolutionary biologist at Queen Mary, University of London, and his colleagues determined that both types of echolocating bats, as well as dolphins, had the same mutations in a particular protein called prestin, which affects the sensitivity of hearing. Looking at other genes known to be involved in hearing, they and other researchers found several others whose proteins were similarly changed in these mammals. © 2012 American Association for the Advancement of Science
Ed Yong Listen very carefully in the rainforests of Brazil and you might hear a series of quiet, high-pitched squeaks. These are the alarm calls of the black-fronted titi (Callicebus nigrifrons), a monkey with a rusty-brown tail that lives in small family units. The cries are loaded with information. Cristiane Cäsar, a biologist at the University of St Andrews, UK, and her colleagues report that the titis mix and match two distinct calls to tell each other about the type of predator that endangers them, as well as the location of the threat. Her results are published in Biology Letters1. Cäsar's team worked with five groups of titis that live in a private nature reserve in the Minas Gerais region of Brazil. When the researchers placed a stuffed caracara — a bird of prey — in the treetops, the titis gave out A-calls, which have a rising pitch. When the animals saw a ground-based threat — represented by an oncilla, a small spotted cat — they produced B-calls, sounds with a falling pitch. However, when the team moved the predator models around, the monkeys tweaked their calls. If the caracara was on the ground, the monkeys started with at least four A-calls before adding B-calls into the mix. If the oncilla was in a tree, the monkeys made a single introductory A-call before switching to B-calls. “A single call doesn’t really tell the recipient what’s happening, but they can infer the type of predator and its location by listening to the first five or six calls,” says co-author Klaus Zuberbühler of the University of Neuchâtel in Switzerland. “The five different groups were almost unanimous in their response. There was no deviation.” © 2013 Nature Publishing Group
By Jason G. Goldman One of the key differences between humans and non-human animals, it is thought, is the ability to flexibly communicate our thoughts to others. The consensus has long been that animal communication, such as the food call of a chimpanzee or the alarm call of a lemur, is the result of an automatic reflex guided primarily by the inner physiological state of the animal. Chimpanzees, for example, can’t “lie” by producing a food call when there’s no food around and, it is thought, they can’t not emit a food call in an effort to hoard it all for themselves. By contrast, human communication via language is far more flexible and intentional. But recent research from across the animal kingdom has cast some doubt on the idea that animal communication always operates below the level of conscious control. Male chickens, for example, call more when females are around, and male Thomas langurs (a monkey native to Indonesia) continue shrieking their alarm calls until all females in their group have responded. Similarly, vervet monkeys are more likely sound their alarm calls when their are other vervet monkeys around, and less likely when they’re alone. The same goes for meerkats. And possibly chimps, as well. Still, these sorts of “audience effects” can be explained by lower-level physiological factors. In yellow-bellied marmots, small ground squirrels native to the western US and southwestern Canada, the production of an alarm call correlates with glucocorticoid production, a physiological measurement of stress. And when researchers experimentally altered the synthesis of glucocorticoids in rhesus macaques, they found a change in the probability of alarm call production. © 2013 Scientific American
by Michael Marshall Life is tough when you're small. It's not just about getting trodden on by bigger animals. Some of the tiniest creatures struggle to make their bodies work properly. This leads to problems that us great galumphing humans will never experience. For instance, the smallest frogs are prone to drying out because water evaporates so quickly from their skin. Miniature animals can't have many offspring, because there is no room in their bodies to grow them. One tiny spider has even had to let its brain spill into its legs, because its head is too small to accommodate it. Gardiner's Seychelles frog is one of the smallest vertebrates known to exist, at just 11 millimetres long. Its tiny head is missing parts of its ears, which means it shouldn't be able to hear anything. It can, though, and that is thanks to its big mouth. One of only four species in the genus Sechellophryne, Gardiner's Seychelles frog is a true rarity. It is confined to a few square kilometres of two islands in the Seychelles, and even if you visit its habitat you're unlikely to see it. That's because the frog spends most of its time in moist leaf litter, so that it doesn't dry out. It eats tiny insects and other invertebrates. When it comes to hearing, it is sadly under-equipped. Unlike most frogs, it doesn't have an external eardrum. Inside its head, it does have the amphibian equivalent of a cochlea, which is the bit that actually detects sounds. But it doesn't have a middle ear to transmit the sound to the cochlea, and is also missing a bone called the columella that would normally help carry the sound. © Copyright Reed Business Information Ltd.
By Katherine Harmon The past couple posts have described some pretty severe experiments on octopuses, including: showing how octopus arms can grow back after inflicted damage and how even severed octopus arms can react to stimuli. (For the record, animals in the studies were anesthetized and euthanized, respectively.) Without getting too far into the woods (or reefs) of animal treatment ethics, the question remains: How much pain and distress can these relatively short-lived invertebrates experience? Luckily for us, a new paper deals with that very question. Researchers from Europe, the UK and Japan teamed up to explore what we know about pain, perception and cognition in octopuses. The findings are described in the special “Cephalopod Research” issue of September’s Journal of Experimental Marine Biology and Ecology. And the issue is not just philo-scientific cloud (or wave) gazing. Starting this year the European Union asks researchers to make similarly humane accommodations for cephalopods as they do for vertebrates (Directive 2010/63/EU, pdf). But, do octopuses experience would-be painful experiences the same way mice do? As the researchers note in their paper, we know very little about whether cephalopods recognize pain or experience suffering and distress in a similar way that we humans—or even we vertebrates—do. Previous (as well as much current) research has looked largely to behavioral clues as an indication to an octopus’s internal state. For example, researchers have observed an octopus’s color changing and activity patterns and looked for any self-inflicted harm (swimming into the side of a tank or eating its own arms) to judge whether the animal is “stressed.” And to tell whether an animal has “gone under” anesthesia, they often look for movements, lack of response, posture change or, at the most, measure heart rate and breathing. © 2013 Scientific American
Karen Ravn It’s safe to say that wildlife biologist Lynn Rogers gets along better with the black bears in Minnesota than with the humans in the state’s Department of Natural Resources. Rogers, a popular bear researcher who has made numerous TV appearances, is engaged in quite a row with the department. At issue: should the department renew Rogers’ permit to study black bears? In June, the department said “no.” But trying to come between Rogers and his bears is a bit like trying to come between a mother bear and her cubs. He took the agency to court, and late last month, the parties came to a temporary agreement. Rogers can keep radio collars on the ten research bears that have them now, but he can’t keep live-streaming video on the Internet from his internationally popular den cams. His case will go back to court in six to nine months. Earlier this month, Rogers received a big boost from renowned chimpanzee researcher Jane Goodall, who wrote to Minnesota governor Mark Dayton praising Rogers and saying that it would be “a scientific tragedy” if his research were ended now. The department gave three reasons for not renewing Rogers’ permit: he hadn’t produced any peer-reviewed publications based on data collected over the past 14 years when he had a permit; his work was endangering the public; and he had engaged in unprofessional conduct. © 2013 Nature Publishing Group
Link ID: 18577 - Posted: 08.29.2013
Daniel Cressey A few chance encounters hundreds of metres underwater seem to have solved the long-standing mystery of what one squid species does with its unusual tentacles: it pretends they are fish to lure its prey into range. Until now, the deep-sea-dwelling squid Grimalditeuthis bonplandi had never been observed in the wild by researchers, and most of the knowledge about it came from partially digested specimens pulled from the stomachs of large fish and whales. Most squid have a pair of tentacles with hooks or suckers that they use to grasp food, but in this species the corresponding tentacles are thin, fragile things — and their function has puzzled squid researchers. Henk-Jan Hoving, a squid researcher at the Helmholtz Centre for Ocean Research in Kiel, Germany, and his team obtained videos of seven of these animals seen in the Atlantic and North Pacific. One of the observations came from an expedition run by the Monterey Bay Aquarium Research Institute in Moss Landing, California, and the other videos were made by commercial remotely-operated submersibles used by the oil and gas industry, and later supplied to Hoving and his team. Hoving and his team saw the squid move the ends of their unique appendages, known as tentacle clubs, in a way that “really looked like a small fish or squid”, he says. They describe their observations in Proceedings of the Royal Society B1. The movement of these tentacles attracts the crustaceans and other cephalopods that G. bonplandi eats. Thinking they are going to get dinner, the prey species move towards the flapping arms, only to be eaten themselves. © 2013 Nature Publishing Group
By BENJAMIN EWEN-CAMPEN This may seem obvious. But in evolutionary terms, the benefits of sexual reproduction are not immediately clear. Male rhinoceros beetles grow huge, unwieldy horns half the length of their body that they use to fight for females. Ribbon-tailed birds of paradise produce outlandish plumage to attract a mate. Darwin was bothered by such traits, since his theory of evolution couldn’t completely explain them (“The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me feel sick!” he wrote to a friend). Moreover, sex allows an unrelated, possibly inferior partner to insert half a genome into the next generation. So why is sex nearly universal across animals, plants and fungi? Shouldn’t natural selection favor animals that forgo draining displays and genetic roulette and simply clone themselves? Yes and no. Many animals do clone themselves; certain sea anemones can bud identical twins from the sides of their bodies. Aphids, bees and ants can reproduce asexually. Virgin births sometimes occur among hammerhead sharks, turkeys, boa constrictors and komodo dragons. But nearly all animals engage in sex at some point in their lives. Biologists say that the benefits of sex come from the genetic rearrangements that occur during meiosis, the special cell division that produces eggs and sperm. During meiosis, combinations of the parents’ genes are broken up and reconfigured into novel arrangements in the resulting sperm and egg cells, creating new gene combinations that might be advantageous. © 2013 Salon Media Group, Inc.