Chapter 6. Evolution of the Brain and Behavior
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By Kate Wong Odds are you carry DNA from a Neandertal, Denisovan or some other archaic human. Just a few years ago such a statement would have been virtually unthinkable. For decades evidence from genetics seemed to support the theory that anatomically modern humans arose as a new species in a single locale in Africa and subsequently spread out from there, replacing archaic humans throughout the Old World without mating with them. But in recent years geneticists have determined that, contrary to that conventional view, anatomically modern Homo sapiens did in fact interbreed with archaic humans, and that their DNA persists in people today. In the May issue of Scientific American, Michael Hammer of the University of Arizona in Tucson examines the latest genetic findings and explores the possibility that DNA from these extinct relatives helped H. sapiens become the wildly successful species it is today. As Scientific American’s anthropology editor, I have an enduring interest in the rise of H. sapiens; and as longtime readers of this blog may know, I’m fascinated (you might even say obsessed) with Neandertals. So naturally I’ve been keen to find out how much, if any, Neandertal DNA I have in my own genome. Several consumer genetic testing companies now test for Neandertal genetic markers as part of their broader ancestry analysis, and after 23andMe lowered the price of their kit to $99 in December, I decided to take the plunge. As it happens, National Geographic’s Genographic Project had recently updated their own genetic test to look for Neandertal DNA, and they sent me a kit (retail price: $299) for editorial review, much as publishers do with new books. And so it was on a chilly Saturday in late January that I found myself spitting into a test tube for 23andMe and swabbing my cheek for the Genographic Project. © 2013 Scientific American
By Susan Milius Zola the crow is about to face a test that has baffled animals from canaries to dogs. She’s a wild New Caledonian crow, and for the first time, she’s seeing a tidbit of meat dangling on a long string tied to a stick. She perches on the stick, bends down, grabs the string with her beak and pulls. But the string is too long. The meat still hangs out of reach. In similar tests, dogs, pigeons and many other species routinely falter. Some nibble at the string or keep tugging and dropping the same segment. Some pull at a string that’s not connected to food just as readily as a string that is. Eventually many get the hang of reeling in the tidbit, but they seem to learn by trial and error. Zola, however, does not fumble. On her first attempt, she anchors the first length of string by stepping on it and immediately bends down again for the next segment. With several more pulls and steps, Zola reels in the treat. Watching the crow, says Russell Gray, one of the researchers behind the string-pulling experiment, “people say, ‘Wow, it had a flash of insight.’ ” At first glance it seems Zola mentally worked through the problem as a human might, devising a solution in an aha moment. But Gray, of the University of Auckland in New Zealand, has had enough of such supposed animal geniuses. Asking whether the crow solves problems in the same way a human would isn’t a useful question, he says. He warns of a roller coaster that scientists and animal lovers alike can get stuck on: first getting excited and romanticizing a clever animal’s accomplishments, then crashing into disappointment when some killjoy comes up with a mundane explanation that’s not humanlike at all. © Society for Science & the Public 2000 - 2013
Sid Perkins The two-million-year-old remains of a novel hominin discovered in August 2008 are an odd blend of features seen both in early humans and in the australopithecines presumed to have preceded them. A battery of six studies1–6 published today in Science scrutinizes the fossils of Australopithecus sediba from head to heel and yields unprecedented insight into how the creature walked, chewed and moved. Together, the studies suggest that this hominin was close to the family tree of early humans — although it remains controversial whether it was one of our direct ancestors. “We see evolution in action across this skeleton,” says Lee Berger, a palaeoanthropologist at the University of the Witwatersrand in Johannesburg, South Africa. For instance, whereas the creature’s arms are ape-like, its hands and wrists are remarkably like those of humans. And although the hominin’s pelvis is shaped like a modern human's, its torso included a narrow upper rib cage like those found in apes. One of the six studies focused on Au. sediba’s teeth1, comparing 22 different aspects across hundreds of teeth from several other species of australopithecines and thousands of early human teeth. Tooth similarities among the species are more likely to signify common ancestry than independent evolution towards a beneficial design, says Debbie Guatelli-Steinberg, an anthropologist at Ohio State University in Columbus. That's because most of the characteristics the team chose to study, such as the subtle curvature of a portion of the tooth’s surface, are not likely to be evolutionarily useful. © 2013 Nature Publishing Group
Link ID: 18027 - Posted: 04.13.2013
by Tanya Lewis, The lip-smacking vocalizations gelada monkeys make are surprisingly similar to human speech, a new study finds. Many nonhuman primates demonstrate lip-smacking behavior, but geladas are the only ones known to make undulating sounds, known as "wobbles," at the same time. (The wobbling sounds a little like a human hum would sound if the volume were being turned on and off rapidly.) The findings show that lip-smacking could have been an important step in the evolution of human speech, researchers say. "Our finding provides support for the lip-smacking origins of speech because it shows that this evolutionary pathway is at least plausible," Thore Bergman of the University of Michigan in Ann Arbor and author of the study published today (April 8) in the journal Current Biology,said in a statement. "It demonstrates that nonhuman primates can vocalize while lip-smacking to produce speechlike sounds." NEWS: Lip Smacks of Monkeys Prelude to Speech? Lip-smacking -- rapidly opening and closing the mouth and lips -- shares some of the features of human speech, such as rapid fluctuations in pitch and volume. (See Video of Gelada Lip-Smacking) Bergman first noticed the similarity while studying geladas in the remote mountains of Ethiopia. He would often hear vocalizations that sounded like human voices, but the vocalizations were actually coming from the geladas, he said. He had never come across other primates who made these sounds. But then he read a study on macaques from 2012 revealing how facial movements during lip-smacking were very speech-like, hinting that lip-smacking might be an initial step toward human speech. © 2013 Discovery Communications, LLC.
Matt Kaplan By making noise that could potentially expose them to predators, young pied babblers get their parents to give them more attentions. Begging loudly has long been viewed as an offspring’s way of saying “I’m hungry”. But in predator-filled environments, these squawks can put young birds in harm's way, and may be a form of blackmail that forces parents to pay attention and feed the youngsters more than they might otherwise. The discovery comes from a three-year analysis of a well-studied community of pied babbler (Turdoides bicolor) in the Kalahari Desert of South Africa1. Alex Thompson of the University of Cape Town and colleagues from Britain and Australia, spent more than 200 hours observing the animals in the wild and recorded more than 3,000 incidents of parents feeding fledglings. Thompson and his team noted that fledglings were fed an average of 0.12 grams of food per minute when on the ground and away from cover, but just 0.03 grams per minute when begging from the safety of the trees. Furthermore, when the birds were played an audio recording of alarm calls indicating that a ground predator was in the vicinity, parents more than doubled the amount they gave to ground-based youngsters, but made no compensation for those in the trees. Fascinated, the team speculated that the young, which were slower than adults to respond to the alarm calls and cannot escape as quickly from danger, were intentionally putting themselves into a dangerous situation when hungry to force their parents to pay attention and feed them. © 2013 Nature Publishing Group,
By DOUGLAS QUENQUA A new study suggests that primates’ ability to see in three colors may not have evolved as a result of daytime living, as has long been thought. The findings, published in the journal Proceedings of the Royal Society B, are based on a genetic examination of tarsiers, the nocturnal, saucer-eyed primates that long ago branched off from monkeys, apes and humans. By analyzing the genes that encode photopigments in the eyes of modern tarsiers, the researchers concluded that the last ancestor that all tarsiers had in common had highly acute three-color vision, much like that of modern-day primates. Such vision would normally indicate a daytime lifestyle. But fossils show that the tarsier ancestor was also nocturnal, strongly suggesting that the ability to see in three colors somehow predated the shift to daytime living. The coexistence of the two normally incompatible traits suggests that primates were able to function during twilight or bright moonlight for a time before making the transition to a fully diurnal existence. “Today there is no mammal we know of that has trichromatic vision that lives during night,” said an author of the study, Nathaniel J. Dominy, associate professor of anthropology at Dartmouth. “And if there’s a pattern that exists today, the safest thing to do is assume the same pattern existed in the past. “We think that tarsiers may have been active under relatively bright light conditions at dark times of the day,” he added. “Very bright moonlight is bright enough for your cones to operate.” © 2013 The New York Times Company
by Lizzie Wade Believe it or not, the gelada monkeys (Theropithecus gelada) on the right may be sharing a good laugh—and possibly the emotions that go along with it. Previously, only humans and orangutans had been shown to quickly and involuntarily mimic the facial expressions of their companions, an ability that seems to be linked to empathy. After spending months observing every playful interaction among the gelada population at Germany's NaturZoo, scientists are ready to add another, more distantly related species to that list. Geladas of all ages were more likely to mimic the play faces of their companions within 1 second of seeing them than they were to respond with a different kind of expression, according to a paper published by the team this week in Scientific Reports. What's more, the fastest and most frequent mimicry responses occurred between mothers and their infant offspring, like the pair pictured on the left. More research is required to determine if geladas are sharing emotional states in addition to facial expressions, but the team suggests that studying the quantity and quality of these mother-child interactions could provide a way forward. © 2010 American Association for the Advancement of Science
By Puneet Kollipara Blind fish that spend their lives in dark, underwater caves have lost a huge chunk of their ability to hear, scientists report in the March 27 Biology Letters. Two of the fish species studied could not hear high-pitched sounds. “I was really surprised,” says study coauthor Daphne Soares of the University of Maryland, College Park. “I expected them to hear much better than the surface fishes.” Cave-dwelling fish can lose their vision and even their eyes over many generations. And without light, eyesight can lose its importance in fish survival. Only two previous studies have explored what happens to hearing after fish lose their vision; both found no differences in hearing between cave fish and those that experience daylight. Soares and her colleagues collected fish of two blind cave-dwelling species, Typhlichthys subterraneus and Amblyopsis spelaea, from lakes in Kentucky. Specimens of a surface-dwelling species, Forbesichthys agassizii, which is closely related to the cave dwellers, came from a lake in south-central Tennessee. Back in the lab, the researchers tested fish hearing by seeing whether sounds across a range of pitches could stimulate nerve activity in the fishes’ brains. The researchers also measured the density of sound-detecting hair cells in the creatures’ ears. © Society for Science & the Public 2000 - 2013
By Meghan Rosen With parasitic flies gorging on her guts and the end approaching, a variable field cricket may have only one thing to do: Find a mate. Usually, female Gryllus lineaticeps prefer males with fast chirps. But when being eaten alive by fly larvae, female crickets don’t wait around for a snappy tune. Instead, they settle for slow-chirping sexual partners, evolutionary biologists Oliver Beckers of Indiana University in Bloomington and William Wagner Jr. of the University of Nebraska-Lincoln report in the April Animal Behaviour. Parasitic flies seek out crickets as potential homes (and meal tickets) for their young. Before the fly larvae chew through crickets’ bellies, female crickets have about a week to find a mate and lay eggs before dying. To find out whether infestation lowered females’ mating standards, Beckers and Wagner placed fly larvae on female crickets and then played slow and fast chirp recordings from loudspeakers set in separate corners of a square chamber. Healthy females walked toward the fast chirping sound about 80 percent of the time, while infested females split their devotion about equally. “They don’t invest a lot of time and energy finding the super sexy guy,” says Becker. “They’ll go for the average Joe.” © Society for Science & the Public 2000 - 2013
by Beth Skwarecki If you thought the battle of the genders was complicated, try having seven sexes. When Tetrahymena, a single-celled creature covered in cilia, mates, the offspring isn't necessarily the same sex as either parent—it can be any of seven. Now, researchers have figured out the complex dance of DNA that determines the offspring's sex, and it's a random selection, they report today in PLOS Biology. Each Tetrahymena has a gene for its own sex—or mating type—in its regular nucleus, but it also carries a second nucleus used only for reproduction. This "germline nucleus" contains incomplete versions of all seven mating type genes, which are cut and pasted together until one complete gene remains and the other six have been deleted. The newly rearranged DNA becomes part of the offspring's regular nucleus, determining its mating type. Because the mating type gene helps Tetrahymena recognize others of a different sex, the researchers say that the finding could shed light on how other cells, including those in humans, recognize those that are different from themselves. © 2010 American Association for the Advancement of Science.
By Susan Milius Hey evolution, thanks for nothing. When a mammal embryo develops, its middle ear appears to form in a pop-and-patch way that seals one end with substandard, infection-prone tissue. “The way evolution works doesn’t always create the most perfect, engineered structure,” says Abigail Tucker, a developmental biologist at King’s College London. “Definitely, it’s made an ear that’s slightly imperfect.” The mammalian middle ear catches sound and transfers it, using three tiny bones that jiggle against the eardrum, to the inner ear chamber. Those three bones — the hammer, anvil and stirrup — are a distinctive trait that distinguishes the group from other evolutionary lineages. Research in mouse embryos finds that the middle ear begins as a pouch of tissue. Then its lining ruptures at one end and the break lets in a different kind of tissue, which forms the tiny bones of the middle ear. This intruding tissue originates from what’s called the embryo’s neural crest, a population of cells that gives rise to bone and muscle. Neural crest tissue has never been known before to create a barrier in the body. Yet as the mouse middle ear forms, this tissue creates a swath of lining that patches the rupture, Tucker and colleague Hannah Thompson, report in the March 22 Science. © Society for Science & the Public 2000 - 2013
by Lizzie Wade Hundreds of millions of years ago, the Earth's seas teemed with trilobites, hard-shelled critters that resembled spiny aquatic cockroaches. Because their exoskeletons lent themselves to fossilization, scientists know a lot about what the outside of their bodies looked like. Their inner workings, however, have remained mysterious. Now, a new study has revealed the structure of the trilobite eye, bringing researchers one step closer to understanding the evolution of vision. Like today's insects and crustaceans, trilobites had compound eyes, with many different lenses focusing light onto clusters of sensory cells lying below them. The resulting image was put together a lot like a picture on your computer screen, with each lens producing one "pixel" of the whole. Because the lenses themselves were made of the mineral calcite, they often fossilized along with the rest of the trilobite's tough exoskeleton. The sensory cells underneath the lenses, however, were ephemeral, and scientists had always assumed that they had decayed without a trace. So imagine Brigitte Schoenemann's surprise when she spotted fossilized versions of these delicate sensory cells while x-raying a long dead trilobite with a computed tomography (CT) scanner. "I expected that we would see [something] in the lens of trilobites, but then suddenly we saw structures of cells below the lens," recalls Schoenemann, a physiologist at the University of Bonn and the University of Cologne, both in Germany. Inspired, she applied to take more fossils to the European Synchrotron Radiation Facility in Grenoble, France, where she could use a particle accelerator's high energy x-rays to peer deeper into the trilobites' eyes. Now, she says, she's created images of the extinct animal's entire visual system, down to the level of fossilized individual cells. © 2010 American Association for the Advancement of Science
by Jennifer Viegas Polly may want a cracker, but when a parrot wants a better deal, it will trade a so-so nut for an even better snack, a new study has found. The discovery, published in the journal Biology Letters, demonstrates that birds can do business in their own way, wheeling and dealing with nuts. It also shows that they can exhibit remarkable self restraint, even performing better than some children. In studies from the 1970s, kids were presented with a marshmallow and were told that they could either eat it now, or wait and receive a second one if they could hold out for a time delay of some minutes. Kids that were able to wait have been more successful now as adults than the other kids (who gulped down the first marshmallow). The ability to strategically wait therefore is very important in the course of human development. Now we can say that it’s important to bird development too. For the new study, Alice Auersperg of the University of Vienna’s Department of Cognitive Biology and colleagues presented an Indonesian cockatoo species, the Goffin’s cockatoo, with food snack options. The best of that bunch, from the bird’s perspective, were pecan nuts. Mirroring the kid-marshmallow experiment, the researchers next offered the birds an even better deal. If the birds did not eat the pecan, they could trade it for a cashew. (Who knew that cockatoos loved cashews so much? Apparently they are the yummiest nut of all, for at least this particular avian species.) © 2013 Discovery Communications, LLC
by Michael Marshall Neanderthals may have had bigger eyes than modern humans, but while this helped them see better, it may have meant that they did not have brainpower to spare for complex social lives. If true, this may have been a disadvantage when the ice age reduced access to food, as they would not have had the skills to procure help from beyond their normal social group, speculates Robin Dunbar at the University of Oxford. Neanderthals' brains were roughly the same size as modern humans, but may have been organised differently. To find out, a team led by Dunbar studied the skulls of 13 Neanderthals and 32 anatomically modern humans. The Neanderthals had larger eye sockets. There are no Neanderthal brains to examine, but primates with larger eyes tend to have larger visual systems in their brains, suggesting Neanderthals did too. Their large bodies would also have required extra brain power to manage. Together, their larger eyes and bodies would have left them with less grey matter to dedicate to other tasks. Neanderthals may have evolved enhanced visual systems to help them see in the gloom of the northern hemisphere, Dunbar says. "It makes them better at detecting things in grim, grey conditions." As a by-product of larger eyes, they may not have been able to expand their frontal lobes – a brain area vital for social interaction – as much as modern humans. As a result, Dunbar estimates they could only maintain a social group size of around 115 individuals, rather than the 150 that we manage. © Copyright Reed Business Information Ltd.
By Scicurious We humans love us some caffeine. The mild stimulant have saved many a student, parent, and hard working adult from nodding over their desks. And it’s a natural product of plants like the coffee plant and the tea bush. But the question is, why do these plants have it in the first place? It turns out that there are two answers to that question. First, caffeine is a natural pesticide, which can paralyze and kill insects that want to chomp on the leaves, berries, or other parts of the plant. It’s good for keeping a bug off your back. But these plants also produce flowers, and these flowers need bees. So it’s somewhat surprising to realize that the coffee plant, as well as plants from the Citrus genus (yup, that means oranges), have caffeine in their nectar. After all, if caffeine is a poison to some bugs, you don’t want to be poisoning your pollinators! But it turns out that bees aren’t like other bugs, and may enjoy themselves a jolt like humans do! Whether they enjoy it or not, they certainly remember it! The authors started out by examining exactly HOW much caffeine was in the nectar of various coffee and citrus plants. And the concentrations of caffeine in the nectar could get up to that of one cup of coffee (though, obviously, in a much smaller volume total). I’m starting to wonder if there’s a “honeyed nectar” energy drink in the future. © 2013 Scientific American
By JAMES GORMAN Nothing kicks the brain into gear like a jolt of caffeine. For bees, that is. And they don’t need to stand in line for a triple soy latte. A new study shows that the naturally caffeine-laced nectar of some plants enhances the learning process for bees, so that they are more likely to return to those flowers. “The plant is using this as a drug to change a pollinator’s behavior for its own benefit,” said Geraldine Wright, a honeybee brain specialist at Newcastle University in England, who, with her colleagues, reported those findings in Science on Thursday. The research, other scientists said, not only casts a new light on the ancient evolutionary interaction between plants and pollinators, but is an intriguing confirmation of deep similarities in brain chemistry across the animal kingdom. Plants are known to go to great lengths to attract pollinators. They produce all sorts of chemicals that affect animal behavior: sugar in nectar, memorable fragrances, even substances in fruit that can act like laxatives in the service of quick seed dispersal. Lars Chittka, who studies bee behavior at Queen Mary, University of London, and wrote a commentary on the research in the same issue of Science, said that in the marketplace of plants seeking pollinators, the plants “want their customers to remain faithful,” thus the sugary nectar and distinctive scents. © 2013 The New York Times Company
by Lizzie Wade With its complex interweaving of symbols, structure, and meaning, human language stands apart from other forms of animal communication. But where did it come from? A new paper suggests that researchers look to bird songs and monkey calls to understand how human language might have evolved from simpler, preexisting abilities. One reason that human language is so unique is that it has two layers, says Shigeru Miyagawa, a linguist at the Massachusetts Institute of Technology (MIT) in Cambridge. First, there are the words we use, which Miyagawa calls the lexical structure. "Mango," "Amanda," and "eat" are all components of the lexical structure. The rules governing how we put those words together make up the second layer, which Miyagawa calls the expression structure. Take these three sentences: "Amanda eats the mango," "Eat the mango, Amanda," and "Did Amanda eat the mango?" Their lexical structure—the words they use—is essentially identical. What gives the sentences different meanings is the variation in their expression structure, or the different ways those words fit together. The more Miyagawa studied the distinction between lexical structure and expression structure, "the more I started to think, 'Gee, these two systems are really fundamentally different,' " he says. "They almost seem like two different systems that just happen to be put together," perhaps through evolution. One preliminary test of his hypothesis, Miyagawa knew, would be to show that the two systems exist separately in nature. So he started studying the many ways that animals communicate, looking for examples of lexical or expressive structures. © 2010 American Association for the Advancement of Science.
By Tina Hesman Saey If someone shouts “look behind you,” tadpoles in Michael Levin’s laboratory may be ready. The tadpoles can see out of eyes growing from their tails, even though the organs aren’t directly wired to the animals’ brains, Levin and Douglas Blackiston, both of Tufts University in Medford, Mass., report online February 27 in the Journal of Experimental Biology. Levin and Blackiston’s findings may help scientists better understand how the brain and body communicate, including in humans, and could be important for regenerative medicine or designing prosthetic devices to replace missing body parts, says Günther Zupanc, a neuroscientist at Northeastern University in Boston. Researchers have transplanted frog eyes to other body parts for decades, but until now, no one had shown that those oddly placed eyes (called “ectopic” eyes) actually worked. Ectopic eyes on tadpoles’ tails allow the animals to distinguish blue light from red light, the Tufts team found. Levin wanted to know whether the brain is hardwired to get visual information only from eyes in the head, or whether the brain could use data coming from elsewhere. To find out, he and Blackiston started with African clawed frog tadpoles (Xenopus laevis) and removed the normal eyes. They then transplanted cells that would grow into eyes onto the animals’ tails. The experiment seemed like a natural to test how well the brain can adapt, Levin says. “There’s no way the tadpole’s brain is expecting an eye on its tail.” Expected or not, some of the tadpoles managed to detect red and blue light from their tail eyes. The researchers placed tadpoles with transplanted eyes in chambers in which half of the chamber was illuminated in blue light and the other half in red light. A mild electric shock zapped the tadpole when it was in one half of the dish so that the animal learned to associate the color with the shock. The researchers periodically switched the colors in the chamber so that the tadpoles didn’t learn that staying still would save them. © Society for Science & the Public 2000 - 2013
by Virginia Morell Every bottlenose dolphin has its own whistle, a high-pitched, warbly "eeee" that tells the other dolphins that a particular individual is present. Dolphins are excellent vocal mimics, too, able to copy even quirky computer-generated sounds. So, scientists have wondered if dolphins can copy each other's signature whistles—which would be very similar to people saying each others' names. Now, an analysis of whistles recorded from hundreds of wild bottlenose dolphins confirms that they can indeed "name" each other, and suggests why they do so—a discovery that may help researchers translate more of what these brainy marine mammals are squeaking, trilling, and clicking about. "It's a wonderful study, really solid," says Peter Tyack, a marine mammal biologist at the University of St. Andrews in the United Kingdom who was not involved in this project. "Having the ability to learn another individual's name is … not what most animals do. Monkeys have food calls and calls that identify predators, but these are inherited, not learned sounds." The new work "opens the door to understanding the importance of naming." Scientists discovered the dolphins' namelike whistles almost 50 years ago. Since then, researchers have shown that infant dolphins learn their individual whistles from their mothers. A 1986 paper by Tyack did show that a pair of captive male dolphins imitated each others' whistles, and in 2000, Vincent Janik, who is also at St. Andrews, succeeded in recording matching calls among 10 wild dolphins "But without more animals, you couldn't draw a conclusion about what was going on," says Richard Connor, a cetacean biologist at the University of Massachusetts, Dartmouth. Why, after all, would the dolphins need to copy another dolphin's whistle? © 2010 American Association for the Advancement of Science
By Erin Wayman BOSTON — The taste for alcohol may be an ancient craving. The ability to metabolize ethanol — the alcohol in beer, wine and spirits — might have originated in the common ancestor of chimpanzees, gorillas and humans roughly 10 million years ago, perhaps when this ancestor became more terrestrial and started eating fruits fermenting on the ground. Chemist Steven Benner of the Foundation for Applied Molecular Evolution in Gainesville, Fla., reached that conclusion by “resurrecting” the alcohol-metabolizing enzymes of extinct primates. Benner and his colleagues estimated the enzymes’ genetic code, built the enzymes in the lab and then analyzed how they work to understand how they changed over time. “It’s like a courtroom re-enactment,” said biochemist Romas Kazlauskas of the University of Minnesota in Minneapolis. Benner “can re-enact what happened in evolution.” Benner proposed the idea February 15 at the annual meeting of the American Association for the Advancement of Science. Today, humans rely on an enzyme called alcohol dehydrogenase 4, or ADH4, to break down ethanol. The enzyme is common throughout the esophagus, stomach and intestines, and is the first alcohol-metabolizing enzyme that comes into contact with what a person drinks. Among primates, not all ADH4s are the same — some can’t effectively metabolize ethanol. © Society for Science & the Public 2000 - 2013