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 Lizzie Wade Neandertals and modern humans had a lot in common—at least enough to have babies together fairly often. But what about their brains? To answer that question, scientists have looked at how Neandertal and modern human brains developed during the crucial time of early childhood. In the first year of life, modern human infants go through a growth spurt in several parts of the brain: the cerebellum, the parietal lobes, and the temporal lobes—key regions for language and social interaction. Past studies suggested baby Neandertal brains developed more like the brains of chimpanzees, without concentrated growth in any particular area. But a new study casts doubt on that idea. Scientists examined 15 Neandertal skulls, including one newborn and a pair of children under the age of 2. By carefully imaging the skulls, the team determined that Neandertal temporal lobes, frontal lobes, and cerebellums did, in fact, grow faster than the rest of the brain in early life, a pattern very similar to modern humans, they report today in Current Biology. Scientists had overlooked that possibility, the researchers say, because Neandertals and Homo sapiens have such differently shaped skulls. Modern humans’ rounded skull is a telltale marker of the growth spurt, for example, whereas Neandertals’ skulls were relatively flat on the top. If Neandertals did, in fact, have fast developing cerebellums and temporal and frontal lobes, they might have been more skilled at language and socializing than assumed, scientists say. This could in turn explain how the children of Neandertal–modern human pairings fared well enough to pass down their genes to so many us living today. © 2016 American Association for the Advancement of Science
By NATALIE ANGIER Their word is their bond, and they do what they say — even if the “word” on one side is a loud trill and grunt, and, on the other, the excited twitterings of a bird. Researchers have long known that among certain traditional cultures of Africa, people forage for wild honey with the help of honeyguides — woodpecker-like birds that show tribesmen where the best beehives are hidden, high up in trees. In return for revealing the location of natural honey pots, the birds are rewarded with the leftover beeswax, which they eagerly devour. Now scientists have determined that humans and their honeyguides communicate with each other through an extraordinary exchange of sounds and gestures, which are used only for honey hunting and serve to convey enthusiasm, trustworthiness and a commitment to the dangerous business of separating bees from their hives. The findings cast fresh light on one of only a few known examples of cooperation between humans and free-living wild animals, a partnership that may well predate the love affair between people and their domesticated dogs by hundreds of thousands of years. Claire N. Spottiswoode, a behavioral ecologist at Cambridge University, and her colleagues reported in the journal Science that honeyguides advertise their scout readiness to the Yao people of northern Mozambique by flying up close while emitting a loud chattering cry. For their part, the Yao seek to recruit and retain honeyguides with a distinctive vocalization, a firmly trilled “brrr” followed by a grunted “hmm.” In a series of careful experiments, the researchers then showed that honeyguides take the meaning of the familiar ahoy seriously. The birds were twice as likely to offer sustained help to Yao foragers who walked along while playing recordings of the proper brrr-hmm signal than they were to participants with recordings of normal Yao words or the sounds of other animals. © 2016 The New York Times Company
By Virginia Morell Infanticide—the killing of offspring—is generally rare among birds. And when it happens, it’s usually because of outsiders that want the nesting site or territory. But what happens among birds, such as the greater ani (Crotophaga major, pictured), which have a more socialist approach to nesting? Two to four pairs of the Central and South American cuckoos (which are usually unrelated) build a single nest, and then work together to raise their chicks, which generally hatch at the same time. Intriguingly, the adults cannot recognize either their own eggs or chicks, so they care for all of them. To find out why—and if the simultaneous hatching protects the chicks from infanticide—a scientist analyzed data on nestling mortality gathered at 104 communal greater ani nests from 2006 to 2015. Of the 741 nestlings, 321 (43%) fledged and 420 (57%) died. Most of the deaths (78.5%) were due to predation. But another 13.8%, or 58 nestlings, died from infanticide, the scientist reports online today in Evolution. The remaining 32 (7.7%) died from starvation. At most of the nests, the chicks hatched within 1 day of each other. Those that first emerged from their eggs were the most likely to be dispatched by one of the nest founders, not an outsider. Chicks that hatched last were also unlucky; weaker than their older and larger nest-mates, they weren’t able to compete for food and starved. Those two pressures—infanticide and food competition—end up favoring the chicks in the middle and those that hatch on the same day, the researcher reports. © 2016 American Association for the Advancement of Science
by Adriana Heguy, molecular biologist and genomics researcher: Interestingly, tongue-curling ability is not solely genetic, and the genetic component may be very small. Monozygotic (identical) twins are not always concordant for tongue-curling ability, so if there is a genetic component, it’s clearly not Mendelian. In other words, it’s not a trait coded by one single gene, and it’s clearly influenced by the environment—in this case, practice. But for some reason this is one of the “myths” about genetics that gets spread around in high school, where it is used as an example of a simple Mendelian trait with a simple dominant-recessive nature. It’s hard to comment on the evolutionary purpose of an ability so heavily influenced by the environment, and not obviously useful. There are many traits for which we do not have the faintest idea why they exist or what purpose they serve. In the case of tongue-curling, it’s possible that it’s a case of fine motor control of the tongue. We need to be able to move our tongues to not bite them when we eat, for example, and for swirling food around. For unknown reasons, some individuals are better than others at controlling tongue movement. And since the ability can be acquired by practicing (though not everybody apparently succeeds), it does seem likely that it is indeed a question of motor control. Most people are able to do it. It’s quite common. But it could be that evolution had nothing to do with it. Or it could be a spandrel; in other words, a side effect of evolution. Maybe the evolution of dexterity or finer motor control of other muscles resulted in tongue “dexterity.” It’s possible that it is an atavism, something that increased tongue muscle control was once useful for tasting or eating certain kinds of foods millions of years ago, and it has not disappeared because the developmental program for fine muscle control is still there.
By Bret Stetka Beloved crank and Seinfeld co-creator Larry David once told an interviewer that he tolerates people like he tolerates lactose — which is to say, I'm assuming, not well. David's particular degree of grumpiness might be extreme, and perhaps embellished in the interest his shtick, but his social misgivings echo those of many in their dotage who’d rather spend time with old friends than deal with the sweat and small talk required to go out and make new ones. Humans may not be alone here. According to new research, our primate cousins also become more socially selective with age, preferring the companionship of their “friends” to monkeys that are less familiar (or maybe just a drag at parties). The findings also hint at a possible evolutionary explanation for why our social preferences change over the years. The work, conducted primarily by researchers from the German Primate Center in Göttingen, Germany, was recently published in the journal Current Biology and entailed observing the behaviors of over 100 Barbary macaque monkeys, an out-going, some might say "screechy," species hailing from North Africa. To get a sense of how interest in non-social vs social stimulation changes over the course of their lifetimes, monkeys of varying ages were observed in the presence of both inanimate objects and other monkeys. They were first presented with three novel objects: animal toys, a see-through cube filled with glitter in a viscous liquid, and a tube baited with food. Those that had reached early adulthood were not interested in the objects without a reward. The younger ones were intrigued by all three. © 2016 Scientific American
by Sarah Zielinski Among people, a man stepping aside to let a woman pass through a door first is seen as a gentlemanly — if a bit old-fashioned — act. Among banana fiddler crabs, though, this behavior is a trap — one that lets a male crab coerce a female into a mating she may not have preferred. To catch the attention of a female and lure her into his burrow, a male banana fiddler crab stands outside the entrance to his cave and waves the larger of his two claws. A female will look him over and consider his size, the color of his claw and how he’s waving it. If she likes what she sees, she’ll approach him. She might decide to enter his burrow and check it out, and once inside, she might stick around for mating if she thinks that the burrow has the right conditions for rearing her embryos. When a female approaches a male and his burrow, most males enter first, letting their potential mate follow him down. But many male crabs take another approach, stepping aside and following her into the lair — letting a male trap the female inside and mate with her, researchers report June 15 in PLOS ONE. Christina Painting of the Australian National University in Canberra and colleagues observed banana fiddler crabs in Darwin, Australia, during two mating seasons, watching what happened as males waved their claws and females made their choice. When a female was interested in a male, the guys entered the burrow first 32 percent of the time. While females were more likely to enter a burrow if a male entered first (71 percent versus only 41 percent when the guy stepped aside), the trapping strategy was more successful in getting a mating out of the meeting. When the male followed the female in, 79 percent of females stuck around the mate. But waiting for her to follow resulted in a pairing only 54 percent of the time. © Society for Science & the Public 2000 - 2016
Nicola Davis Death by cannibalism might seem like a high price to pay for a fleeting moment of passion, but male praying mantises are doing it for the kids, new research suggests. Scientists have discovered that female praying mantises who eat their mates after sex produce a greater number of eggs than those who do not, with the bodies of the ill-fated males used to aid their production. Of the species of praying mantises known to exhibit sexual cannibalism it is estimated up to 28% of males are eaten by their partner. After mating, the female stores the male’s sperm and later uses it to fertilise the eggs that she produces. The authors say the new study backs up a long-mooted theory that males could have evolved a behavioural trait of self-sacrifice to boost their reproductive success. “There is an obvious cost – you are dead, you have lost all future mating possibilities,” said William Brown, of the State University of New York at Fredonia, who co-authored the research. “We measure costs and benefit in terms of offspring production,” he added. If, by dying, the male can boost the number of offspring produced by one female, the theory goes, it could outweigh the downsides of missing out on future conquests. Published in the journal Proceedings of the Royal Society B by researchers in the US and Australia, the new study reveals how scientists unpicked the influence of cannibalism on the production of offspring in the praying mantis Tenodera sinensis, by tracking what happened to male ejaculate and bodily tissues after mating. © 2016 Guardian News and Media Limited
By Patrick Monahan The soft, blinking lights of fireflies aren’t just beautiful—they may also play a role in creating new species. A new study shows that using light-up powers for courtship makes species split off from each other at a faster pace, providing some of the clearest evidence yet that the struggle to find mates shapes the diversity of life. The firefly’s glow, like the enormous claws of fiddler crabs and the elaborate dances of manakins, was sculpted by the struggle for sex. Scientists have long thought that this kind of mating-driven natural selection—called “sexual selection”—could make species split into two. Say females in two populations prefer different color patterns in males: Even if the populations have the same needs in every other way, that simple preference could make them split into species with males of separate colors. “A lot of closely related species differ in sexual traits,” says Emily Ellis, an evolutionary biologist at the University of California (UC), Santa Barbara. But actually linking this kind of evolution to species proliferation is a hard idea to test. “So many people have looked at this and found differing results,” she says—possibly because they looked at smaller groups, like birds, rather than across the whole tree of life. That’s where bioluminescence comes in. Many groups of living organisms, from insects to fish to octopuses, emit light, whether to ward off predators, dazzle prey, or attract mates. It’s a trait that has evolved more than 40 times across the animal kingdom, Ellis says. © 2016 American Association for the Advancement of Science.
By Vinicius Donisete Goulart The “new world” monkeys of South and Central America range from large muriquis to tiny pygmy marmosets. Some are cute and furry, others bald and bright red, and one even has an extraordinary moustache. Yet, with the exception of owl and howler monkeys, the 130 or so remaining species have one thing in common: A good chunk of the females, and all of the males, are colorblind. This is quite different from “old world” primates, including us Homo sapiens, who are routinely able to see the world in what we humans imagine as full color. In evolutionary terms, colorblindness sounds like a disadvantage, one which should really have been eliminated by natural selection long ago. So how can we explain a continent of the colorblind monkeys? I have long wondered what makes primates in the region colorblind and visually diverse, and how evolutionary forces are acting to maintain this variation. We don’t yet know exactly what kept these seemingly disadvantaged monkeys alive and flourishing—but what is becoming clear is that colorblindness is an adaptation not a defect. The first thing to understand is that what we humans consider “color” is only a small portion of the spectrum. Our “trichromatic” vision is superior to most mammals, who typically share the “dichromatic” vision of new world monkeys and colorblind humans, yet fish, amphibians, reptiles, birds, and even insects are able to see a wider range, even into the UV spectrum. There is a whole world of color out there that humans and our primate cousins are unaware of. What is becoming clear is that color blindness is an adaptation not a defect.
James Gorman There’s an aura of power around invasive species. How is it that they can sweep in and take over from the locals? Are they more adaptable, tougher? What are their secrets? The great-tailed grackle is a case in point. North America has its own similar species — the common and boat-tailed grackle. But the great-tailed bird, Quiscalus mexicanus, native to Central America, is one of the most invasive species in the United States. The black birds with iridescent feathers were prized by the Aztec emperor Auitzotl, who, by some accounts, relocated some of them from Veracruz to near Mexico City about 500 years ago. Over the past century or so the bird has spread north and its range is still expanding, particularly in the West, where it haunts cattle feed lots and big dairy farms. The birds are also quite happy in urban areas, like Santa Barbara, Calif., where Corina J. Logan captured and later released some grackle for recent experiments. Great-tailed grackles first caught the attention of Dr. Logan, now at Cambridge University, in 2004 when she was doing undergraduate research in Costa Rica. “They’ll actually walk right up and look you in the eye,” she said. “They look like they’re so smart.” Years later, having earned her Ph.D. at Cambridge, she decided to look more closely at them because she was interested in behavioral flexibility. Grackles, for example, might look under rocks at the beach for something to eat, or switch to discarded sandwich wrappers in a city park. © 2016 The New York Times Company
By Sarah Kaplan Some 250 million years ago, when dinosaurs roamed the Earth and early mammals were little more than tiny, fuzzy creatures that scurried around attempting to evade notice, our ancestors evolved a nifty trick. They started to become active at night. They developed sensitive whiskers and an acute sense of hearing. Their circadian rhythms shifted to let them sleep during the day. Most importantly, the composition of their eyes changed — instead of color-sensing cone photoreceptor cells, they gained thousands of light-sensitive rod cells, which allowed them to navigate a landscape lit only by the moon and stars. Mammals may no longer have to hide from the dinosaurs, but we bear the indelible marks of our scrappy, nocturnal past. Unlike every other vertebrate on land and sea, we still have rod-dominated eyes — human retinas, for example, are 95 percent rods, even though we're no longer active at night. "How did that happen? What is the mechanism that made mammals become so different?" asked Anand Swaroop, chief of the Neurobiology Neurodegeneration and Repair Laboratory at the National Eye Institute. He provides some answers to those questions in a study published in the journal Developmental Cell Monday. The findings are interesting from an evolutionary standpoint, he said, but they're also the keys to a medical mystery. If Swaroop and his colleagues can understand how our eyes evolved, perhaps they can fix some of the problems that evolved with them.
By NATALIE ANGIER At birth, the least weasel is as small and light as a paper clip, and the tiny ribs that press visibly against its silvery pink skin give it a segmented look, like that of an insect. A newborn kit is exceptionally underdeveloped, with sealed eyes and ears that won’t open for five or six weeks, an age when puppies and kittens are ready to be weaned. A mother weasel, it seems, has no choice but to deliver her young half-baked. As a member of the mustelid clan — a noble but often misunderstood family of carnivorous mammals that includes ferrets, badgers, minks and wolverines — she holds to a slender, elongated body plan, the better to pursue prey through tight spaces that most carnivores can’t penetrate. Bulging baby bumps would jeopardize that sylphish hunting physique. The solution? Give birth to the equivalent of fetuses and then finish gestating them externally on mother’s milk. “If you want access to small environments, you can’t have a big belly,” said William J. Zielinski, a mustelid researcher with the United States Forest Service in Arcata, Calif. “You don’t see fat weasels.” For Dr. Zielinski and other mustelid-minded scientists, weasels exemplify evolutionary genius and compromise in equal measure, the piecing together of exaggerated and often contradictory traits to yield a lineage of fierce, fleet, quick-witted carnivores that can compete for food against larger celebrity predators like the big cats, wolves and bears. Researchers admit that wild mustelids can be maddening to study. Most species are secretive loners, shrug off standard radio collars with ease, and run close to the ground “like small bolts of brown lightning,” as one team noted. Now you see them, no, you didn’t. Nevertheless, through a mix of dogged field and laboratory studies, scientists have lately made progress in delineating the weasel playbook, and it’s a page turner, or a page burner. © 2016 The New York Times Company
Link ID: 22321 - Posted: 06.14.2016
By C. CLAIBORNE RAY Insects have an odor-sensing system that is roughly analogous to that of vertebrates, according to “The Neurobiology of Olfaction,” a survey published in 2010. Different species have varying numbers of odor receptors, special molecules that are attuned to specific odor molecules. Genes govern the production of each kind of receptor; the more genes, the more kinds of receptor. A big difference with insects is that their olfactory receptors are basically external, often within hairlike groups of cells, called sensilla, on the antennas, not inside a collection organ like a nose. Sign Up for the Science Times Newsletter Every week, we'll bring you stories that capture the wonders of the human body, nature and the cosmos. The odorant molecules encounter odorant-binding proteins, assumed to guide them to the long receptor nerve cells, called axons. Electrical signals are sent along the axons. The axons are usually connected to specific processing centers in the brain called glomeruli, held in a region called the antennal lobe. There the signals are analyzed. Depending on the nature, quantity and timing of the odor signals received, still other cells appear to excite or inhibit reactions. Exactly how the reaction system works is not yet fully understood. The Florida carpenter ant and the Indian jumping ant both have wide-ranging abilities to sense odors, with more than 400 genes to make different odor receptors, a 2012 study found. The fruit fly has only 61. The research also found marked differences in the smelling ability of the sexes, with the female ants well ahead. © 2016 The New York Times Company
By Devi Shastri Calling someone a “bird brain” might not be the zinger of an insult you thought it was: A new study shows that—by the total number of forebrain neurons—some birds are much brainier than we thought. The study, published online today in the Proceedings of the National Academy of Sciences, found that 28 bird species have more neurons in their pallial telencephalons, the brain region responsible for higher level learning, than mammals with similar-sized brains. Parrots and songbirds in particular packed in the neurons, with parrots (like the gray parrot, above) ranging from 227 million to 3.14 billion, and songbirds—including the notoriously intelligent crow—from 136 million to 2.17 billion. That’s about twice as many neurons as primates with brains of the same mass and four times as many as rodent brains of the same mass. To come up with their count, the researchers dissected the bird brains and then dissolved them in a detergent solution, ensuring that the cells were suspended in what neuroscientist Suzana Herculano-Houzel of Vanderbilt University in Nashville calls “brain soup.” This allowed them to label, count, and estimate how many neurons were in a particular brain region. The region that they focused on allows some birds to hone skills like tool use, planning for the future, learning birdsong, and mimicking human speech. One surprising finding was that the neurons were much smaller than expected, with shorter and more compact connections between cells. The team’s next step is to examine whether these neurons started out small or instead shrank in order to keep the birds light enough for flights. One thing, at least, is clear: It’s time to find a new insult for your less brainy friends. © 2016 American Association for the Advancement of Science
Michael Graziano Ever since Charles Darwin published On the Origin of Species in 1859, evolution has been the grand unifying theory of biology. Yet one of our most important biological traits, consciousness, is rarely studied in the context of evolution. Theories of consciousness come from religion, from philosophy, from cognitive science, but not so much from evolutionary biology. Maybe that’s why so few theories have been able to tackle basic questions such as: What is the adaptive value of consciousness? When did it evolve and what animals have it? The Attention Schema Theory (AST), developed over the past five years, may be able to answer those questions. The theory suggests that consciousness arises as a solution to one of the most fundamental problems facing any nervous system: Too much information constantly flows in to be fully processed. The brain evolved increasingly sophisticated mechanisms for deeply processing a few select signals at the expense of others, and in the AST, consciousness is the ultimate result of that evolutionary sequence. If the theory is right—and that has yet to be determined—then consciousness evolved gradually over the past half billion years and is present in a range of vertebrate species. Even before the evolution of a central brain, nervous systems took advantage of a simple computing trick: competition. Neurons act like candidates in an election, each one shouting and trying to suppress its fellows. At any moment only a few neurons win that intense competition, their signals rising up above the noise and impacting the animal’s behavior. This process is called selective signal enhancement, and without it, a nervous system can do almost nothing. © 2016 by The Atlantic Monthly Group
By Rachel Feltman Archerfish are already stars of the animal kingdom for their stunning spit-takes. They shoot high-powered water jets from their mouths to stun prey, making them one of just a few fish species known to use tools. But by training Toxotes chatareus to direct those jets of spit at certain individuals, scientists have shown that the little guys have another impressive skill: They seem to be able to distinguish one human face from another, something never before witnessed in fish and spotted just a few times in non-human animals. The results, published Tuesday in the Nature journal Scientific Reports, could help us understand how humans got so good at telling each other apart. Or how most people got to be good at that, anyway. I'm terrible at it. It's generally accepted that the fusiform gyrus, a brain structure located in the neocortex, allows humans to tell one another apart with a speed and accuracy that other species can't manage. But there's some debate over whether human faces are so innately complex — and that distinguishing them is more difficult than other tricks of memory or pattern recognition — that this region of the brain is a necessary facilitator of the skill that evolved especially for it. Birds, which have been shown to distinguish humans from one another, have the same structure. But some researchers still think that facial recognition might be something that humans learn — it's not an innate skill — and that the fusiform gyrus is just the spot where we happen to process all the necessary information.
By Virginia Morell Sex is never simple—even among lizards. Unlike mammals, the sex of central bearded dragons, large lizards found in eastern Australia, is determined by their chromosomes and the environment. If the eggs are incubated in high temperatures, male embryos turn into females. Such sex-reversed lizards still retain the chromosomal makeup of a male, but they develop into functional superfemales, whose output of eggs exceeds that of the regular females. Now, a new study predicts that—in some cases—these superfemales may be able to drive regular ones to extinction. That’s because superfemales not only produce more eggs, but they’re also exceptionally bold. Looking at the shape, physiology, and behavior of 20 sex-reversed females, 55 males, and 40 regular females, scientists found that the sex-reversed dragons were physically similar to regular males: They had a male dragon’s long tail and high body temperature. They were also behaviorally similar, acting like bold, active males—even as they produced viable eggs. Indeed, the scientists report in the current issue of the Proceedings of the Royal Society B that these sex-reversed females were behaviorally more malelike than the genetic males. Because of these advantages, this third sex could reproductively outcompete normal females, the scientists say, possibly causing some populations to lose the female sex chromosome. (Females are the heterogametic sex, like human males.) In such a population, the dragons’ sex would then be determined solely by temperature instead of genetics—something that’s occurred in the lab within a single generation. Could it happen in the wild? The scientists are still investigating. © 2016 American Association for the Advancement of Science
By Karin Brulliard Think about how most people talk to babies: Slowly, simply, repetitively, and with an exaggerated tone. It’s one way children learn the uses and meanings of language. Now scientists have found that some adult birds do that when singing to chicks — and it helps the baby birds better learn their song. The subjects of the new study, published last week in the journal Proceedings of the National Academy of Sciences, were zebra finches. They’re good for this because they breed well in a lab environment, and “they’re just really great singers. They sing all the time,” said McGill University biologist and co-author Jon Sakata. The males, he means — they’re the singers, and they do it for fun and when courting ladies, as well as around baby birds. Never mind that their melody is more “tinny,” according to Sakata, than pretty. Birds in general are helpful for vocal acquisition studies because they, like humans, are among the few species that actually have to learn how to make their sounds, Sakata said. Cats, for example, are born knowing how to meow. But just as people pick up speech and bats learn their calls, birds also have to figure out how to sing their special songs. Sakata and his colleagues were interested in how social interactions between adult zebra finches and chicks influences that learning process. Is face-to-face — or, as it may be, beak-to-beak — learning better? Does simply hearing an adult sing work as well as watching it do so? Do daydreaming baby birds learn as well as their more focused peers? © 1996-2016 The Washington Post
By Simon Makin Other species are capable of displaying dazzling feats of intelligence. Crows can solve multistep problems. Apes display numerical skills and empathy. Yet, neither species has the capacity to conduct scientific investigations into other species' cognitive abilities. This type of behavior provides solid evidence that humans are by far the smartest species on the planet. Besides just elevated IQs, however, humans set themselves apart in another way: Their offspring are among the most helpless of any species. A new study, published recently in Proceedings of the National Academy of Sciences (PNAS), draws a link between human smarts and an infant’s dependency, suggesting one thing led to the other in a spiraling evolutionary feedback loop. The study, from psychologists Celeste Kidd and Steven Piantadosi at the University of Rochester, represents a new theory about how humans came to possess such extraordinary smarts. Like a lot of evolutionary theories, this one can be couched in the form of a story—and like a lot of evolutionary stories, this one is contested by some scientists. Kidd and Piantadosi note that, according to a previous theory, early humans faced selection pressures for both large brains and the capacity to walk upright as they moved from forest to grassland. Larger brains require a wider pelvis to give birth whereas being bipedal limits the size of the pelvis. These opposing pressures—biological anthropologists call them the “obstetric dilemma”—could have led to giving birth earlier when infants’ skulls were still small. Thus, newborns arrive more immature and helpless than those of most other species. Kidd and Piantadosi propose that, as a consequence, the cognitive demands of child care increased and created evolutionary pressure to develop higher intelligence. © 2016 Scientific American
By David Z. Hambrick If you’re a true dog lover, you take it as one of life’s simple truths that all dogs are good, and you have no patience for scientific debate over whether dogs really love people. Of course they do. What else could explain the fact that your dog runs wildly in circles when you get home from work, and, as your neighbors report, howls inconsolably for hours on end when you leave? What else could explain the fact that your dog insists on sleeping in your bed, under the covers—in between you and your partner? At the same time, there’s no denying that some dogs are smarter than others. Not all dogs can, like a border collie mix named Jumpy, do a back flip, ride a skateboard, and weave through pylons on his front legs. A study published in the journal Intelligence by British psychologists Rosalind Arden and Mark Adams confirms as much. Consistent with over a century of research on human intelligence, Arden and Adams found that a dog that excels in one test of cognitive ability will likely excel in other tests of cognitive ability. In more technical terms, the study reveals that there is a general factor of intelligence in dogs—a canine “g” factor. For their study, Arden and Adams devised a battery of canine cognitive ability tests. All of the tests revolved around—you guessed it—getting a treat. In the detour test, the dog’s objective was to navigate around barriers arranged in different configurations to get to a treat. In the point-following test, a researcher pointed to one of two inverted beakers concealing a treat, and recorded whether the dog went to that beaker or the other one. Finally, the quantity discrimination test required the dog to choose between a small treat (a glob of peanut butter) and a larger one (the “correct” answer). Arden and Adams administered the battery to 68 border collies from Wales; all had been bred and trained to do herding work on a farm, and thus had similar backgrounds. © 2016 Scientific American