MONKEY GROUP BEHAVIOR

Most Old World monkeys live in groups led by a dominant male and comprised of lesser males, and females and their young. In most groups there are twice as many females as males, with non-group males either living alone or living in a group with other males. Most of the males within the group are juveniles that will eventually leave. New World monkeys, many of whom live in dense forests, tend to more often live in monogamous pairs.
A male Old World monkey usually gains control of a group one of two ways: either by defeating a dominant male in a group and taking over his group and by luring some females away from a group to form his own group. Within a group the females often get along fairly well. They usually have some sort of ranking system. The males may live peacefully or fight depending in the group, its dynamic, the species and availability of food and females.
These rules don’t apply to all monkeys and apes. In some primate species males hold on to dominance thanks to the collective support of females. In others the females are dominant. In others still dominance and hierarchy are irrelevant concepts.
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Male Dominance in Rhesus Monkeys and the Rostral Prefrontal Cortex
Commenting on the findings in a paper by Jerome Sallet and his colleagues at Oxford University published in the journal Science,Robert M. Sapolsky wrote in the Los Angeles Times: “Male rhesus monkeys are among the least Dalai Lama-esque of primates. They form strict, linear dominance hierarchies, and the highest-ranking guy holds his position through aggression and intimidation, something primatologists call a "despotic" dominance system. Rhesus males are often brutish and combative. [Source: Robert M. Sapolsky, Los Angeles Times, January 15, 2012. Sapolsky is a professor of neuroscience at Stanford University and the author of "A Primate's Memoir," among other books.]
Sallet and his team studied the behaviors of the rhesus males in different social groups, figuring out the hierarchies. Then, with those behavioral data in hand, the researchers scanned the brains of the monkeys using magnetic resonance imaging to determine the size of different parts of the subjects' brains. Looking at the brain this way is informative — because size matters. A region that has been working hard tends to increase in size, while those that are mothballed get smaller. Spend a summer learning how to juggle, say, and the part of the cortex devoted to hand-eye coordination expands. Go through a horrific experience that results in post-traumatic stress disorder and you'll probably end up with an enlarged amygdala, a part of the brain that is centrally involved in processing fear and anxiety. Conversely, lose your hearing and your "auditory cortex" will atrophy.

rhesus monkey
When the researchers scrutinized the monkeys' brains, all sorts of interesting findings popped up. One involved the issue of dominance. After controlling for such factors as age, weight and size of the social group, out popped a clear correlation: The higher a male's rank, the larger the average size of a particular brain region. Was this a region that controls the muscles required to pummel a rival? Were these the neurons that cause testosterone to be secreted? No and no.
The size increase was in a region far from the world of muscles and androgenic hormones, a region called the rostral prefrontal cortex. This area of the brain has to do with social smarts, with drawing inferences based on information about what other individuals can see, what they know, what they think (something psychologists call "theory of mind"). In humans, people with more gray matter in that region are better at understanding multiple layers of human interaction. They'd be good, for example, at the virtually impossible task of keeping track of who, in "A Midsummer Night's Dream," is in love with whom, and who thinks he might know who is in love with whom. In other words, this is a brain region central to being able to understand someone else's perspective.
A study like this can't tell you whether a big rostral prefrontal cortex causes a male to become high-ranking, whether it's the other way around, or whether it is neither of those things. What it shows is that on average, the size of a part of the brain centrally involved in social intelligence is a good predictor of high rank, a cool and novel finding.
Republicans Display Monkey-Like Dominance Behavior
In January 2012, in the middle of the Republican primaries, Robert M. Sapolsky wrote in the Los Angeles Times: Now that Michele Bachmann has dropped out of the race for the GOP presidential nomination, we are left with an array of the usual suspects in American politics — namely a bunch of men who seem to spend much of their lives bragging about how tough they are. [Source: Robert M. Sapolsky, Los Angeles Times, January 15, 2012. Sapolsky is a professor of neuroscience at Stanford University and the author of "A Primate's Memoir," among other books.]
“We have Rick Perry waxing macho about the number of executions he's overseen in Texas and Rick Santorum threatening to bomb Iran. There's Newt Gingrich proclaiming that the race is going to boil down to being between "Newt and not-Newt." Even the septuagenarian Ron Paul starts his campaign appearances with Darth Vader's theme music, which he uses to emphasize how dangerous he is to Mitt Romney. As any zoologist would instantly recognize, what we have here are a bunch of male primates vying for dominance.
“And there is an instructive lesson here for this presidential season. As the candidates vie to show how tough they are on Iran, the national debt and those suffering polar bears trying to foist the myth of global warming on us, we should think about those high-ranking, bully-boy rhesus monkeys and their large rostral prefrontal cortexes. It's likely that politicians too have developed parts of their brain that could be put to better use than feuding and posturing. Perhaps it's time for humans to demand that our leaders use their brains for more than coordinating the muscles responsible for chest thumping.
Capuchin Monkey Fairness Experiment
Capuchin monkeys have a strong sense of fairness, even going strike over pay issues. In a famous experiment they refused to do a task and threw down tools their when they saw another monkey get a bigger reward for doing the same task. John Whitfield wrote in Nature: “The experiments show that notions of justice extend beyond humans, says Sarah Brosnan of Emory University in Atlanta, Georgia. This is probably an innate ability that evolved in our primate ancestor, she believes: "You need a sense of fairness to live in large, complex groups." Brosnan and her colleague Frans de Waal taught brown capuchin monkeys (Cebus apella) to swap plastic tokens for food. Normally, monkeys were happy to exchange a token for some cucumber. [Source: John Whitfield, Nature, September 18, 2003 ]
“But the monkeys took offence if they saw a neighbour getting a grape for a token. In about half of such trials, the short-changed capuchin either refused to hand over its token, or rejected the reward. Some threw the token or cucumber clean out of their cage. The animals' umbrage was even greater if another monkey got a grape for nothing. About 80 percent rebelled in some way in this situation. "It's a really neat discovery," says primatologist Charles Janson of the State University of New York at Stony Brook. "The monkey is clearly paying attention to what its neighbour is doing, and realizing that it's getting a better reward."
See Separate Article: HUMAN-LIKE BEHAVIOR AND MORALITY IN CHIMPANZEES, MONKEYS AND ORANGUTANS factsanddetails.com
Monkeys Respond to Social Cues Much Like Humans

A groundbreaking study on groups of vervet monkeys published April 2013 in the journal Science suggests that social learning may have a greater influence on behavior development than previously thought. Pam Belluck wrote in the New York Times: “If you are eating lunch in Pittsburgh or Dallas, you might grab a sandwich. But should you get transferred to Paris, you will probably eat like the French: multicourse sit-down lunches. plus a glass of wine. But it turns out people are not the only ones who make monkey-see-monkey-do cultural shifts. Monkeys, and apparently several other species, do, too. [Source: Pam Belluck, New York Times, April 25, 2013]
“In a clever study researchers showed that when Vervet monkeys roam, they act in when-in-Rome fashion. Wild Vervet monkeys, trained to eat only pink-dyed or blue-dyed corn and shun the other color, quickly began eating the disliked-color corn when they moved from a pink-preferred setting to a blue-is-best place, and vice versa. The switch occurred even though both corn colors were equally accessible, side-by-side in open containers. Scientists said the monkeys relinquished their color convictions because they saw the locals eating the hated hue.
“The findings addressed a long-contentious question among animal experts: is animal behavior determined only by genes and individual learning, or can animals, like humans, learn socially? “Culture was thought to be something only humans had,” said Carel van Schaik, an evolutionary anthropologist at the University of Zurich who was not involved in the study. “But if you define culture as socially transmitted knowledge, skills and information, it turns out we see some of that in animals. Now this experiment comes along and I must say it really blew me away.” He added: “Imagine you’ve just learned to eat pink corn and for a while blue corn was really bad, but then you move to an area where it’s the opposite and basically you wipe your slate clean. You think, ‘Oh, these locals, they must know what’s the best thing.’ ”
“Other studies have found similar learning abilities in social animals. In the same issue of Science, researchers reported that by observing others, humpback whales learned to whack the water with their tail fins to attract prey. But while previous research often relied on anecdotes, observations or animals in captivity, the monkey study documented social learning in wild animals. “We long believed that cultural transmission was important,” said Frans de Waal, a primatologist at Emory University who did not take part in the study. “But I never thought it would be at the scale where the results would be so strong.”
“The scientists set out pink and blue corn in adjacent Tupperware containers for four groups of wild monkeys in neighboring regions in a South African reserve. A study leader, Erica van de Waal, a researcher at University of St. Andrews in Scotland, said she wanted to use red and blue, shades monkeys are known to see because they are the colors of male Vervet genitalia. But South African grocery stores stocked mostly blue and pink food coloring because people use them for cakes celebrating girl and boy birthdays. After trying vinegar and chilies to make corn taste bitter, researchers settled on soaking corn in acrid-tasting aloe leaves. Pink corn was “aloe treated” for two groups; blue for the other two. Soon, monkeys in each group consistently rejected the colored corn soaked in aloe leaves.
“After several months, researchers stopped treating the corn with aloe, but monkeys continued eating only the color that had never been made bitter. Dominant monkeys never sampled the disliked color; subordinate monkeys might, but only if dominants were hogging the liked color. Baby monkeys, which received no color training, instantly ate only what their mothers ate, even squatting on the other color, “totally ignoring that there was an edible color under their feet,” Dr. van de Waal said.
“Most strikingly, when male monkeys migrated from a different-colored region, they ate the local color. The one exception was a blue-is-best male who entered a pink area with no dominant male, took control and continued eating blue corn. But he “might be a stupid male that had too much testosterone and was just not looking at what the others are doing,” Dr. van de Waal said.
Monkey Appears to Resuscitate Electrocuted Friend in India
In December 2014, Associated Press reported: Onlookers at a train station in northern India watched in awe as a monkey came to the rescue of an injured friend — resuscitating another monkey that had been electrocuted and knocked unconscious. The injured monkey had fallen between the tracks, apparently after touching high-tension wires at the train station in the north Indian city of Kanpur. [Source: Associated Press, December 25, 2014]
His companion came to the rescue and was captured on camera lifting the friend’s motionless body, shaking it, dipping it into a mud puddle and biting its head and skin — working until the hurt monkey regained consciousness. After about 20 minutes, the injured monkey opened its eyes and began moving again.
The monkeys were rhesus macaques. Dr. Apu Nahir states, “It is simply amazing. The monkey dipped the other primate into the river, for set intervals, then visibly checked for a pulse. It also utilized the recovery position, a technique taught to field medics when dealing with post-seizure, post-drowning or post-shock victims. If this monkey is not evolved of cerebral ability, I would have to guess that reincarnation is true and this monkey was a medic in a past life.” [Source: Annabelle Goodman, December 24, 2014]
Was monkey actually trying to revive shocked companion? Luisa Arnedo, a National Geographic grants program officer who earned her Ph.D. studying primates, told National Geographic: There is little research into how nonhuman primates deal with death since the events are seldom observed. However, scientists have occasionally seen primates react to death, "in many cases by shaking the body of the dead animal, as not accepting its immobility, and also reacting by rough behaviors seemingly aimed at reanimation." [Source: Brian Clark Howard, National Geographic, December 23, 2014]
Chimpanzees have been seen becoming very quiet when a member of their group dies, especially if it is a high-ranking individual, Arnedo adds. And primate mothers will sometimes carry the mummified bodies of their babies for weeks or even months, "as if denying the loss of their baby." It's unclear whether these behaviors are intentional, Arnedo says.
"In this particular case, does the male shaking the body of the injured individual know that by shaking it and dropping it in water, it can reanimate it?" she asks. It's difficult to say. Arnedo calls the video "an amazing representation of the complexity of primate behavior," and says "it is a reminder of how much we still don't understand about their societies and their reactions, and how much is left to do for those studying primates."
Drunken Monkey Hypothesis
Monkeys' attraction to sugar-rich and ethanol-containing fruit may explain our own attraction to alcohol, some researchers believe. In 2004 Dustin Stephens observed a howler monkey feasting on bright orange fruits of a kind of palm tree in the tropical rain forest on Panama's Barro Colorado Island. Dustin Stephens and Robert Dudley wrote in Natural History magazine, “ Climbing onto the branches of a neighboring tree to reach the untouched clusters, the forager first sniffed the fruit then frantically began to eat: sometimes dropping partly eaten fruits onto the forest floor. Risking a thirty-foot fall and serious injury from the enormous spines of the palm tree, the monkey seemed as fearless as a drunken teenager. [Source: Dustin Stephens and Robert Dudley, Natural History magazine, December 2004]
“Our assays of the fruit he dropped suggested why: He may, in fact, have been drunk. Our calculations showed iliat the reckless forager had consumed the monkey equivalent of ten "standard drinks" during his twenty-minute gorging session. This measurement was the first quantitative estimate the amount of alcohol ingested by a wild primate ever made. It also fitted nicely with the 'drunken monkey" hypothesis, developed earlier by Robert Dudley.
“The hypothesis proposes that a strong addiction to the smell and taste of alcohol conferred a selective advantage on our primate ancestors by helping them locate nutritious fruit at the peak of ripeness. Millions of years later, in the Middle Ages, people learned to distill spirits, which potently concentrated the natural alcoholic content of fermented fruits and grain. The once advantageous appetite for alcohol became a danger to human health and well-being. Drawing on yeast biology, fruit ripening, biological anthropology, human generics, and the emerging field of Darwinian medicine, the drunken monkey hypothesis could ultimately contribute to understanding — and perhaps even mitigating — the enormous damage done by alcohol.
“The drunken monkey hypothesis goes like this: for 40 million years primate diets have included substantial quantities of fruit. In the warm humid tropics, where humans evolved, yeast on the fruit skins and within the fruit convert sugars into various forms of alcohol, the most common being ethanol. Ethanol is a light molecule that disperses readily, and the downwind odor of ethanol is a reliable sign of ripe fruit. In the tropical forest where most primates live, the competition for ripe fruit is intense. For a hungry monkey, then, a good foraging strategy would be to follow the smell of alcohol to the fruit and eat it in a hurry.
Evidence of Drunken Monkey Hypothesis
Dustin Stephens and Robert Dudley wrote in Natural History magazine, “Fossilized teeth show that fruit has been a major component of the primate diet since the mid- to late- Holocene Epoch, between 5 million and 34 million years ago. Some of our closest relatives — chimpanzees, orangutans, and certain populations of gorillas — eat diets based primarily on fruit. [Source: Dustin Stephens and Robert Dudley, Natural History magazine, December 2004]
“The place to begin is the relation between ripe fruit and alcohol. Yeasts that occur on fruit consume sugar in the fruit as a source of energy, in a process known as anaerobic* fermentation ("anaerobic," because it takes place in the absence of oxygen). As the fruit ripens, and the yeast gets going, the ethanol content of the fruit rises rapidly, For example, the unripened fruit of the Astrocaryum palm contains no ethanol; ripe hanging fruit is about 0.6 percent ethanol by weight; overripe fruit, often fallen to the ground, can have an ethanol content of more than 4 percent. The monkey that Stephens observed on Barro Colorado Island was feasting on fruit near its peak ripeness when its ethanol content is about 1 percent.
“What is the evidence that our primate relatives (or other organisms) are attracted to alcohol as a sign of nutrition? It is known that fruit flies follow increasing concentrations of ethanol vapor as a way to find the ripe fruit within which they lay their eggs. A similar sensory mechanism is likely at play in other speciels, including primates. The excessive consumption of fruit due to alcohol, similar to the one seen on Barro Colorado, have been observed several times in monkeys. ln each instance, the monkey risked life and limb while eating quickly from bunch after bunch of Astrocaryum fruits, sometimes committing its full weight to a fruit cluster without even securing its tail to a branch for safety. Other observations from the rainforest describe what seems to be fruit-induced intoxication in butterflies, fruit flies, a variety of birds, fruit bats, elephants, and several other primate species.
“It is possible, of course, that drunken behavior is simply an accident without a deep evolutionary context. Maybe rainforest animals just like to have fun, But some evidence implies that the connection between alcohol and nutrition is deeper than that, at least for primates. Initial observations of monkeys on Barro Colorado show that they prefer ripe fruits with moderate levels of alcohol. They avoid unripe fruits with no alcohol as well as overripe fruits with more alcohol but less sugar (by then, most of the sugar has been converted to alcohol). We note that people, too, often drink alcohol while eating, suggesting that drink with food is a natural combination. And various experiments have shown that having an alcoholic drink before a meal increases both the time spent eating and the number of calories consumed.
“If there really is an evolutionary connection between alcohol and primate nutrition, an important conclusion follows: Alcohol was least in moderation- cannot be entirely harmful to health. lf it were, a good nose for alcohol would not have given an advantage to our primate ancestors. In any event, a wide range of evidence suggests that moderate consumption of alcohol is healthful for various organisms. Fruit flies, for instance, live longer and have more offspring when they are experimentally exposed to vapors containing intermediate levels of ethanol than they do when exposed to a lot of it or to none at all. ln people, too, moderate alcohol consumption seems to be mofe healthful than too much or too little.
“A variety of direct and circumstantial evidence suggests that in our deep evolutionary background, alcohol and nutrition (and consequently, alcohol and survival) were related. For some of our close genetic relatives, rainforest observations show that they remain related to this day. Furthermore, some evidence shows that intermediate levels of alcohol consumption are beneficial to human health. But if evolution has rendered alcohol so good for us, why is it now such a problem? The answer, we think, lies in a mismatch between our species’ long evolutionary past and the techno-cultural environment we have created in the past few centuries. Until well into primate evolution, the amount of alcohol our ancestors could consume was strictly limited. As we have noted, even overripe fruits have an ethanol content of only about 4 percent, and they are not the ones favored by monkeys. That picture did not change substantially even when modern humans, some 10,000 years ago, learned to control fermentation.
Monkeys and Television
The Yomiuri Shimbun reported: “Humans are not the only primates that enjoy watching TV. In an article published in a Swiss specialist journal a team from the Kyoto University Primate Research Institute found that monkeys enjoyed themselves based on monitoring the monkeys’ brain activity while it watched TV. Feelings of anger and fear were evident from the monkey's facial expression, but feelings of joy could only be induced. [Source: Yomiuri Shimbun, June 20, 2010]
The team, led by Prof. Nobuo Masataka, used optical topography to observe what parts of a rhesus monkey's brain were activated when it watched TV. Optical topography uses near-infrared light to record brain activity. The team found the frontal lobe of the monkey's brain was activated by watching TV. This is the same part that is activated in humans when they feel joy, such as when a baby sees its mother smile.
In the experiment, the monkey watched a video of an elephant and a giraffe performing in a circus, and another of a monkey grooming itself. Its brain showed more activity when it watched the circus. An increasing number of zoos have been showing their animals TV to break up the monotonous living environment. The research team has scientifically confirmed the effectiveness of the zoos' strategy, observers said.
Image Sources: Wikimedia Commons
Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.
Last updated December 2024