Chapter 6. Evolution of the Brain and Behavior
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Bruce Bower Hunter-gatherers and farming villagers who live in worlds without lightbulbs or thermostats sleep slightly less at night than smartphone-toting city slickers, researchers say. “Contrary to conventional wisdom, people in societies without electricity do not sleep more than those in industrial societies like ours,” says UCLA psychiatrist and sleep researcher Jerome Siegel, who was not involved in the new research. Different patterns of slumber and wakefulness in each of these groups highlight the flexibility of human sleep — and also point to potential health dangers in how members of Western societies sleep, conclude evolutionary biologist David Samson of Duke University and colleagues. Compared with other primates, human evolution featured a shift toward sleeping more deeply over shorter time periods, providing more time for learning new skills and knowledge as cultures expanded, the researchers propose. Humans also evolved an ability to revise sleep schedules based on daily work schedules and environmental factors such as temperature. Samson’s team describes sleep patterns in 33 East African Hadza hunter-gatherers over a total of 393 days in a paper published online January 7 in the American Journal of Physical Anthropology. The team’s separate report on slumber among 21 rural farmers in Madagascar over 292 days will appear later this year in the American Journal of Human Biology. |© Society for Science & the Public 2000 - 201
By Helen Briggs BBC News The idea that dogs are more intelligent than cats has been called into question. Japanese scientists say cats are as good as dogs at certain memory tests, suggesting they may be just as smart. A study - involving 49 domestic cats - shows felines can recall memories of pleasant experiences, such as eating a favourite snack. Dogs show this type of recollection - a unique memory of a specific event known as episodic memory. Humans often consciously try to reconstruct past events that have taken place in their lives, such as what they ate for breakfast, their first day in a new job or a family wedding. These memories are linked with an individual take on events, so they are unique to that person. Saho Takagi, a psychologist at Kyoto University, said cats, as well as dogs, used memories of a single past experience, which may imply they have episodic memory similar to that of humans. "Episodic memory is viewed as being related to introspective function of the mind; our study may imply a type of consciousness in cats," she told BBC News. "An interesting speculation is that they may enjoy actively recalling memories of their experience like humans." The Japanese team tested 49 domestic cats on their ability to remember which bowl they had already eaten out of and which remained untouched, after a 15-minute interval. © 2017 BBC
By NANCY L. SEGAL and SATOSHI KANAZAWA In 1973, the biologist Robert Trivers and the computer scientist Dan Willard made a striking prediction about parents and their offspring. According to the principles of evolutionary theory, they argued, the male-to-female ratio of offspring should not be 50-50 (as chance would dictate), but rather should vary as a function of how good (or bad) the conditions are in which the parents find themselves. Are the parents’ resources plentiful — or scarce? The Trivers-Willard hypothesis holds that when their conditions are good, parents will have more male offspring: Males with more resources are likely to gain access to more females, thereby increasing the frequency with which their genes (and thus their parents’ genes) are preserved in future generations. Conversely, male offspring that lack resources are likely to lose out to males that have more resources, so in bad conditions it pays for parents to “invest” more in daughters, which will have more opportunities to mate. It follows, as a kind of corollary, that when parents have plentiful resources they will devote those resources more to their sons, whereas when resources are scarce, parents will devote them more to their daughters. In short: If things are good, you have more boys, and give them more stuff. If things are bad, you have more girls, and give more of your stuff to them. Is this hypothesis correct? In new research of ours, to be published in the April issue of The Journal of Experimental Child Psychology, we suggest that in the case of breast-feeding, at least, it appears to be. In recent years, evidence has emerged suggesting that in various mammalian species, breast milk — which is, of course, a resource that can be given to children — is tailored for the sex of each offspring. For example, macaque monkey mothers produce richer milk (with higher gross energy and fat content) for sons than for daughters, but also provide greater quantities of milk and higher concentrations of calcium for daughters than for sons. © 2017 The New York Times Company
By NICHOLAS ST. FLEUR The tale of the Tasmanian tiger was tragic. Once numerous across Tasmania, the doglike marsupial was branded a sheep killer by colonists in the 1830s and hunted to extinction. The last of its kind, Benjamin, died in a zoo in 1936, and with it many secrets into the animals’ lives were lost. The striped creature, which is also known as the thylacine, was hardly studied when it was alive, depriving scientists of understanding the behavior of an important predator from Australia’s recent biological past. Now, for the first time, researchers have performed neural scans on the extinct carnivore’s brain, revealing insights that had been lost since the species went extinct. “Part of the myth about them is what exactly did they eat, how did they hunt and were they social?” said Dr. Gregory Berns, a neuroscientist at Emory University and lead author on the study, which was published Wednesday in the journal PLOS One. “These are questions nobody really knows the answers to.” Dr. Berns’s main research pertains to dogs and the inner workings of the canine brain, but after learning more about Tasmanian tigers, he became fascinated by the beasts. With their slender bodies, long snouts and sharp teeth, Tasmanian tigers looked as if they could be related to dogs, wolves or coyotes. But actually they are separated by more than 150 million years of evolution. It is a classic example of convergent evolution, in which two organisms that are not closely related develop similar features because of the environment they adapted to and the ecological role they played. To better understand thylacines, Dr. Berns spent two years tracking down two preserved Tasmanian tiger brains, one at the Smithsonian Institution and the other at the Australian Museum. Their brains, like those of all marsupials, are very different from the brains of placental mammals. The biggest difference is that they lack a corpus callosum, which is the part of the brain that connects the left and right hemispheres. © 2017 The New York Times Company
Claudia Dreifus Geneticists tell us that somewhere between 1 and 5 percent of the genome of modern Europeans and Asians consists of DNA inherited from Neanderthals, our prehistoric cousins. At Vanderbilt University, John Anthony Capra, an evolutionary genomics professor, has been combining high-powered computation and a medical records databank to learn what a Neanderthal heritage — even a fractional one — might mean for people today. We spoke for two hours when Dr. Capra, 35, recently passed through New York City. An edited and condensed version of the conversation follows. Q. Let’s begin with an indiscreet question. How did contemporary people come to have Neanderthal DNA on their genomes? A. We hypothesize that roughly 50,000 years ago, when the ancestors of modern humans migrated out of Africa and into Eurasia, they encountered Neanderthals. Matings must have occurred then. And later. One reason we deduce this is because the descendants of those who remained in Africa — present day Africans — don’t have Neanderthal DNA. What does that mean for people who have it? At my lab, we’ve been doing genetic testing on the blood samples of 28,000 patients at Vanderbilt and eight other medical centers across the country. Computers help us pinpoint where on the human genome this Neanderthal DNA is, and we run that against information from the patients’ anonymized medical records. We’re looking for associations. What we’ve been finding is that Neanderthal DNA has a subtle influence on risk for disease. It affects our immune system and how we respond to different immune challenges. It affects our skin. You’re slightly more prone to a condition where you can get scaly lesions after extreme sun exposure. There’s an increased risk for blood clots and tobacco addiction. To our surprise, it appears that some Neanderthal DNA can increase the risk for depression; however, there are other Neanderthal bits that decrease the risk. Roughly 1 to 2 percent of one’s risk for depression is determined by Neanderthal DNA. It all depends on where on the genome it’s located. © 2017 The New York Times Company
By Avi Selk “Oh Long Johnson,” a cat once said, back in the primordial history of Internet memes. “Oh Don Piano. Why I eyes ya.” Or so said the captions — appended to the gibberish of a perturbed house cat on “America's Funniest Home Videos” in 1999 and rediscovered in the YouTube era, when millions of people heard something vaguely human echo in a distant species. It was weird. And hilarious. And just maybe, profound. As the “Oh Long Johnson” craze was fading a few years ago, a wave of scientific discoveries about apes and monkeys began upending old assumptions about the origins of language. Only humans could willfully control their vocal tracts, went the established wisdom. Until Koko the gorilla coughed on command. Surely, then, our vowels were ours alone. But this month, researchers picked up British ohs in the babble of baboons. Study after study is dismantling a hypothesis that has stood for decades: that the seeds of language did not exist before modern humans, who got all the way to Shakespeare from scratch. And if so much of what we thought we knew about the uniqueness of human speech was wrong, some think it's time to take a second look at talking pet tricks. “It's humbling to understand that humans, in the end, are just another species of primate,” said Marcus Perlman, who led the Koko study in 2015. © 1996-2017 The Washington Post
Ian Sample Science editor Tempting as it may be, it would be wrong to claim that with each generation humans are becoming more stupid. As scientists are often so keen to point out, it is a bit more complicated than that. A study from Iceland is the latest to raise the prospect of a downwards spiral into imbecility. The research from deCODE, a genetics firm in Reykjavik, finds that groups of genes that predispose people to spend more years in education became a little rarer in the country from 1910 to 1975. The scientists used a database of more than 100,000 Icelanders to see how dozens of gene variants that affect educational attainment appeared in the population over time. They found a shallow decline over the 65 year period, implying a downturn in the natural inclination to rack up qualifications. But the genes involved in education affected fertility too. Those who carried more “education genes” tended to have fewer children than others. This led the scientists to propose that the genes had become rarer in the population because, for all their qualifications, better educated people had contributed less than others to the Icelandic gene pool. Spending longer in education and the career opportunities that provides is not the sole reason that better educated people tend to start families later and have fewer children, the study suggests. Many people who carried lots of genes for prolonged education left the system early and yet still had fewer children that the others. “It isn’t the case that education, or the career opportunities it provides, prevents you from having more children,” said Kari Stefansson, who led the study. “If you are genetically predisposed to have a lot of education, you are also predisposed to have fewer children.” © 2017 Guardian News and Media Limited
By Virginia Morell Only three known species go through menopause: killer whales, short-finned pilot whales, and humans. Two years ago, scientists suggested whales do this to focus their attention on the survival of their families rather than on birthing more offspring. But now this same team reports there’s another—and darker—reason: Older females enter menopause because their eldest daughters begin having calves, leading to fights over resources. The findings might also apply to humans, the scientists say. “What an interesting paper,” says Phyllis Lee, a behavioral ecologist at the University of Stirling in the United Kingdom, who was not involved in the study. “It brings two perspectives on menopause neatly together, and provides an elegant model for its rarity.” The new work came about when Darren Croft, a behavioral ecologist at the University of Exeter in the United Kingdom, and his colleagues looked back on their 2015 killer whale menopause study. “That showed how they helped and why they lived so long after menopause, but it didn’t explain why they stop reproducing,” he says, noting that in other species, such as elephants, older females also share wisdom and knowledge with their daughters, but continue to have calves. © 2017 American Association for the Advancement of Science.
By Peter Godfrey-Smith Adapted from Other Minds: The Octopus, the Sea and the Deep Origins of Consciousness, by Peter Godfrey-Smith. Copyright © 2016 by Peter Godfrey-Smith. Someone is watching you, intently, but you can't see them. Then you notice, drawn somehow by their eyes. You're amid a sponge garden, the seafloor scattered with shrublike clumps of bright orange sponge. Tangled in one of these sponges and the gray-green seaweed around it is an animal about the size of a cat. Its body seems to be everywhere and nowhere. The only parts you can keep a fix on are a small head and the two eyes. As you make your way around the sponge, so, too, do those eyes, keeping their distance, keeping part of the sponge between the two of you. The creature's color perfectly matches the seaweed, except that some of its skin is folded into tiny, towerlike peaks with tips that match the orange of the sponge. Eventually it raises its head high, then rockets away under jet propulsion. A second meeting with an octopus: this one is in a den. Shells are strewn in front, arranged with some pieces of old glass. You stop in front of its house, and the two of you look at each other. This one is small, about the size of a tennis ball. You reach forward a hand and stretch out one finger, and one octopus arm slowly uncoils and comes out to touch you. The suckers grab your skin, and the hold is disconcertingly tight. It tugs your finger, tasting it as it pulls you gently in. The arm is packed with sensors, hundreds of them in each of the dozens of suckers. The arm itself is alive with neurons, a nest of nervous activity. Behind the arm, large round eyes watch you the whole time. © 2017 Scientific American
By Tanya Lewis To the untrained listener, a bunch of babbling baboons may not sound like much. But sharp-eared experts have now found that our primate cousins can actually produce humanlike vowel sounds. The finding suggests the last common ancestor of humans and baboons may have possessed the vocal machinery for speech—hinting at a much earlier origin for language than previously thought. Researchers from the National Center for Scientific Research (CNRS) and Grenoble Alpes University, both in France, and their colleagues recorded baboons in captivity, finding the animals were capable of producing five distinct sounds that have the same characteristic frequencies as human vowels. As reported today in PLoS ONE, the animals could make these sounds despite the fact that, as dissections later revealed, they possess high voice boxes, or larynxes, an anatomical feature long thought to be an impediment to speech. “This breaks a serious logjam” in the study of language, says study co-author Thomas Sawallis, a linguist at the University of Alabama. “Theories of language evolution have developed based on the idea that full speech was only available to anatomically modern Homo sapiens,” approximately 70,000 to 100,000 years ago, he says, but in fact, “we could have had the beginnings of speech 25 million years ago.” The evolution of language is considered one of the hardest problems in science, because the process left no fossil evidence behind. One practical approach, however, is to study the mechanics of speech. Language consists roughly of different combinations of vowels and consonants. Notably, humans possess low larynxes, which makes it easier to produce a wide range of vowel sounds (and as Darwin observed, also makes it easier for us to choke on food). A foundational theory of speech production, developed by Brown University cognitive scientist Philip Lieberman in the 1960s, states the high larynxes and thus shorter vocal tracts of most nonhuman primates prevents them from producing vowel-like sounds. Yet recent research calls Lieberman’s hypothesis into question. © 2017 Scientific American
By Victoria Gill Science reporter, BBC News Researchers have used camera traps to film tool-use that is unique to chimpanzees in Ivory Coast. The footage revealed that the clever primates habitually make special water-dipping sticks - chewing the end of the stick to turn it into a soft, water-absorbing brush. Primate researchers examined the "dipping sticks" and concluded they were made specifically for drinking. The findings are reported in the American Journal of Primatology. Lead researcher Juan Lapuente, from the Comoe Chimpanzee Conservation Project, in Ivory Coast, explained that using similar brush-tipped sticks to dip into bees' nests for honey was common in chimpanzee populations across Africa. "But the use of brush-tipped sticks to dip for water is completely new and had never been described before," he told BBC News. "These chimps use especially long brush tips that they make specifically for water - much longer than those used for honey." The researchers tested the chimps' drinking sticks in an "absorption experiment", which showed that the particularly long brush-tips provided an advantage. "The longer the brush, the more water they collect," said Mr Lapuente. "This technology allows Comoe chimpanzees to obtain water from extremely narrow and deep tree holes that only they - and no other animal - can exploit, which [gives] them a superb adaptive advantage to survive in this dry and unpredictable environment." © 2017 BBC.
Link ID: 23075 - Posted: 01.10.2017
By Drake Baer Convergent evolution is what happens when nature takes different courses from different starting points to arrive at similar results. Consider bats, birds, and butterflies developing wings; sharks and dolphins finding fins; and echidnas and porcupines sporting spines. Or, if you want to annoy a traditionalist scientist, talk about humans and octopuses — and how they may both have consciousness. This is the thrust of Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness, a new book by the scuba-diving, biology-specializing philosopher Peter Godfrey-Smith, originally of Australia and now a distinguished professor at the City University of New York’s graduate center. The book was written up by Olivia Judson in The Atlantic, and you should read the whole thing, but what I find mesmerizing is how categorically other the eight-tentacled ink-squirters are, and how their very nature challenges our conceptualizations of intelligence. “If we can make contact with cephalopods as sentient beings, it is not because of a shared history, not because of kinship, but because evolution built minds twice over,” Godfrey-Smith is quoted as saying. “This is probably the closest we will come to meeting an intelligent alien.” (He’s not the first to think so: The Hawaiian creation myth holds that octopuses are the only creatures left over from an earlier incarnation of the Earth, making them more proto-terrestrials than extraterrestrials.) © 2016, New York Media LLC.
By STEPH YIN Inuit who live in Greenland experience average temperatures below freezing for at least half of the year. For those who live in the north, subzero temperatures are normal during the coldest months. Given these frigid conditions, anthropologists have wondered for decades whether the Inuit in Greenland and other parts of the Arctic have unique biological adaptations that help them tolerate the extreme cold. A new study, published on Wednesday in Molecular Biology and Evolution, identifies gene variants in Inuit who live in Greenland, which may help them adapt to the cold by promoting heat-generating body fat. These variants possibly originated in the Denisovans, a group of archaic humans who, along with Neanderthals, diverged from modern humans about half a million years ago. “As modern humans spread around the world, they interbred with Denisovans and Neanderthals, who had already been living in these different environments for hundreds of thousands of years,” said Rasmus Nielsen, a professor of integrative biology at the University of California, Berkeley and an author of the paper. “This gene exchange may have helped some modern humans adapt to and conquer new environments.” The new study follows earlier research by Dr. Nielsen and colleagues, which found genetic mutations that might help the Inuit metabolize unsaturated fatty acids common in their diet of whales, seals and fish. In this study, Dr. Nielsen’s team focused on another distinct region in the Inuit genome, which seems to affect body fat distribution and other aspects of development. The researchers compared the genomes of nearly 200 Inuit with genomes of Neanderthals, Denisovans and modern populations around the world. © 2016 The New York Times Company
Link ID: 23011 - Posted: 12.23.2016
Ramin Skibba The high-pitched squeals of the humble bat may be as complex as the calls of dolphins and monkeys, researchers have found. A study published on 22 December in Scientific Reports1 reveals that the fruit bat is one of only a few animals known to direct its calls at specific individuals in a colony, and suggests that information in the calls of many social animals may be more detailed than was previously thought. Bats are noisy creatures, especially in their crowded caves, where they make calls to their neighbours. “If you go into a fruit-bat cave, you hear a cacophony,” says Yossi Yovel, a neuroecologist at Tel Aviv University in Israel who led the study. Until now, it has been difficult to separate this noise into distinct sounds, or to determine what prompted the individual to make a particular call. “Animals make sounds for a reason,” says Whitlow Au, a marine-bioacoustics scientist at the University of Hawaii at Manoa. “Most of the time, we don’t quite understand those reasons.” To find out what bats are talking about, Yovel and his colleagues monitored 22 captive Egyptian fruit bats (Rousettus aegyptiacus) around the clock for 75 days. They modified a voice-recognition program to analyse approximately 15,000 vocalizations collected during this time. The program was able to tie specific sounds to different social interactions captured by video, such as when two bats fought over food. © 2016 Macmillan Publishers
By Claire Asher We pride ourselves on our big brains, but when it comes to figuring out whether people or other animals with particularly big brains do better than others, the evidence has been lacking. Now, for the first time, a study in red deer is showing that bigger brained mammals tend to be more successful in the wild, and that brain size is a heritable trait that they can pass on to their offspring. Corina Logan from the University of Cambridge and her team have looked at the skulls of 1314 red deer (Cervus elaphus) from the Isle of Rum. The complete life histories of the deer are well known thanks to the Isle of Rum Red Deer Project, which has been collecting data on the island for more than 40 years, spanning seven deer generations. “This kind of study has not been conducted before because it requires long-term data from a large number of individuals,” says Logan. Heritable heads The team found that the ratio of skull volume to body size was highly heritable, explaining 63 per cent of variation between individuals. Female deer with larger skulls lived significantly longer and raised more offspring to adulthood, though it’s not clear yet why bigger brains are advantageous to females. © Copyright Reed Business Information Ltd.
Carl Zimmer Primates are unquestionably clever: Monkeys can learn how to use money, and chimpanzees have a knack for game theory. But no one has ever taught a nonhuman primate to say “hello.” Scientists have long been intrigued by the failure of primates to talk like us. Understanding the reasons may offer clues to how our own ancestors evolved full-blown speech, one of our most powerful adaptations. On Friday, a team of researchers reported that monkeys have a vocal tract capable of human speech. They argue that other primates can’t talk because they lack the right wiring in their brains. “A monkey’s vocal tract would be perfectly adequate to produce hundreds, thousands of words,” said W. Tecumseh Fitch, a cognitive scientist at the University of Vienna and a co-author of the new study. Human speech results from a complicated choreography of flowing air and contracting muscles. To make a particular sound, we have to give the vocal tract a particular shape. The vocal tracts of other primates contain the same elements as ours — from vocal cords to tongues to lips — but their geometry is different. That difference long ago set scientists to debating whether primates could make speechlike sounds. In the 1960s, Philip H. Lieberman, now a professor emeritus of Brown University, and his colleagues went so far as to pack a dead monkey’s vocal tract with plaster to get a three-dimensional rendering. © 2016 The New York Times Company
By Michael Price The famed parrot Alex had a vocabulary of more than 100 words. Kosik the elephant learned to “speak” a bit of Korean by using the tip of his trunk the way people whistle with their fingers. So it’s puzzling that our closest primate cousins are limited to hoots, coos, and grunts. For decades, monkeys’ and apes’ vocal anatomy has been blamed for their inability to reproduce human speech sounds, but a new study suggests macaque monkeys—and by extension, other primates—could indeed talk if they only possessed the brain wiring to do so. The findings might provide new clues to anthropologists and language researchers looking to pin down when humans learned to speak. “This certainly shows that the macaque vocal tract is capable of a lot more than has previously been assumed,” says John Esling, a linguist and phonetics expert at the University of Victoria in Canada, who was not involved with the work. The study’s lead author, William Tecumseh Sherman Fitch III, an evolutionary biologist and cognitive scientist at the University of Vienna, says the question of why monkeys and apes can’t speak goes back to Darwin. (Yes, Fitch is the great-great-great-grandson of U.S. Civil War General William Tecumseh Sherman.) Darwin thought nonhuman primates couldn’t talk because they didn’t have the brains, he says. But over time, anthropologists instead embraced the idea that the primates’ vocal tracts were holding them back: They simply lacked the flexibility to produce the wide range of vowels present in human speech. That remains the “textbook answer” today, Fitch says. © 2016 American Association for the Advancement of Science.
By Sam Wong Size matters. Bigger genitals mean more mating success for male mosquito fish, a relative of the guppy. But the development of longer male organs prompts females to evolve bigger brains to help them escape overeager mates. Mating among mosquito fish is far from romantic. The male makes no effort to court partners, instead sneaking up and attempting to copulate by force up to a thousand times a day. It uses a modified anal fin, the gonopodium, to deliver sperm into the female. In this sort of mating system, the relationship between males and females can resemble that between predators and prey, which commonly involve an evolutionary arms race where adaptations on one side are closely matched by changes on the other. For example, big-brained predators tend to prey on big-brained prey, as the two try to outsmart each other. Séverine Buechel and colleagues at Stockholm University in Sweden wondered if a similar arms race was going on between male and female mosquito fish. Do females evolve bigger brains to defend against sneaky males, and do males evolve bigger brains in response? To test this, the team looked at what happened to brain size when males were bred to have longer gonopodia. Male mosquito fish have long gonopodia compared with related species in which coercion is not the dominant mating strategy, and males with longer gonopodia tend to be more successful at mating. The researchers found that breeding more well-endowed males led to bigger-brained females. But there was no arms race: male brains didn’t get bigger at the same time. © Copyright Reed Business Information Ltd.
By Helen Briggs BBC News Humans may in part owe their big brains to a DNA "typo" in their genetic code, research suggests. The mutation was also present in our evolutionary "cousins" - the Neanderthals and Denisovans. However, it is not found in humans' closest living relatives, the chimpanzees. As early humans evolved, they developed larger and more complex brains, which can process and store a lot of information. Last year, scientists pinpointed a human gene that they think was behind the expansion of a key brain region known as the neocortex. They believe the gene arose about five or six million years ago, after the human line had split off from chimpanzees. Now, researchers have found a tiny DNA change - a point mutation - that appears to have changed the function of the gene, sparking the process of expansion of the neocortex. It may have paved the way for the brain's expansion by dramatically boosting the number of brain cells found in this region. Dr Wieland Huttner of the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany, led the research. "A point mutation in a human-specific gene gave it a function that allows expansion of the relevant stem cells that make a brain big," he told BBC News. "This one, as it is fixed in the human genome - so all living humans have the gene - apparently gave a tremendous selection advantage, and that's why we believe it spread in the human population." Between two and six million years ago, the ancestors of modern humans began to walk upright and use simple tools.
Carrie Arnold There was one sound that biologist Rusty Gonser always heard at Cranberry Lake — and there was one sound that he would never hear again. Every summer for more than 25 years, Gonser and his wife, Elaina Tuttle, had made the trip to this field station in the Adirondack Mountains — a 45-minute boat ride from the nearest road. Now, as he moored his boat to the shaky wooden dock, he heard a familiar and short song that sounded like 'oh-sweet-Canada'. The whistle was from a white-throated sparrow calling hopefully for a mate. What he didn't hear was the voice or laughter of his wife. For the first time, Gonser was at Cranberry Lake alone. Just a few weeks earlier, Tuttle had died of breast cancer. Her entire career, and most of Gonser's, had been devoted to understanding every aspect of the biology of the white-throated sparrow (Zonotrichia albicollis). Less than six months before she died this year at the age of 52, the couple and their team published a paper1 that was the culmination of that work. It explained how a chance genetic mutation had put the species on an extraordinary evolutionary path. The mutation had flipped a large section of chromosome 2, leaving it unable to pair up with a partner and exchange genetic information. The more than 1,100 genes in the inversion were inherited together as part of a massive 'supergene' and eventually drove the evolution of two different 'morphs' — subtypes of the bird that are coloured differently, behave differently and mate only with the opposite morph. Tuttle and Gonser's leap was to show that this process is nearly identical to the early evolution of certain sex chromosomes, including the human X and Y. The researchers realized that they were effectively watching the bird evolve two sex chromosomes, on top of the two it already had. © 2016 Macmillan Publishers Limited,