The order of primates includes 15 families, 77 genera and approximately 280 species and 626 taxa (species and subspecies) that have lived in the past 5000 years. Two of the families and 11 genera are extinct. There are two main genuses of primate: 1) prosimians (lemurs, lorises and galagos); and 2) anthropoids (monkeys, apes and humans). Tarsiers, another kind of primate, are most closely related to prosimians but also have anthropoid features. The largest primates are mountain gorillas. The smallest are mouse lemurs, that weigh only 24 to 38 grams. The largest primate ever was a Pleistocene ape that lived in China and Vietnam and weighed 300 kilograms.

Most primates live in tropical or subtropical areas and can be found in all tropical and subtropical areas of the world except Australia and New Guinea. They eat a wide variety food and display a wide variety of behaviors and are regarded as one of the most diverse mammal groups.

In Asia, there are around 75 species of primate in 13 genera. The number of species is comparable to that of Africa even though Africa has a much larger area inhabitable for primates. The reason for this is that southern Asia has many islands, isolated peninsulas and regions divided by mountains that allow isolated populations to become different species.

However the number of species found in a particular community is relatively small. It is not exactly clear why this is the case. Some scientists have arged that this because of the high number of non-fruiting dipterocarp tress. About 34 percent of the primates in Asia are regarded as threatened or endangered.

News: “Primate Conservation “is a newsletter first published in 1981; “Asian Primates” is a newsletter first published in 1991.

Primate History

The oldest primate fossils date to around 55 million years ago. There is circumstantial evidence based on mathematics and probability that they lived as far back as 80 million years which would have made them contemporaries of the dinosaurs.

Ancient prosimians (the group that includes lemurs and lorises) are believed to have originated in the Northern Hemisphere (North America or Europe) 65 million years ago. Promisians appeared in the fossil record in both the Old World (Europe and Asia) and the New World (the Americas) about 55 million years ago. Many of the traits they developed — sterosciopic vision, grasping hands, large brains and superior muscular coordination and dexterity — grew out of the fact they lived in trees.

It was long thought that anthropoids appeared in Africa about 35 million years, presumably evolving from prosimians. Now there is evidence that anthropoid lineage is as old as the prosimian one and both may have arisen as long as 60 million years ago. It is widely believed to that at around this time primates divided onto two major lineages: one that led to anthropoids and the other that led to modern prosimians. The first anthropoids were a diverse group, with around 40 genera.

Some paleontologists now argue that anthropoids arose in Asia, not Africa. The oldest known anthropoid fossils from Africa were found in Algeria and the Fayum oasis area of Egypt. They date to between 50 million and 37 million years ago and were smaller creatures, in many cases smaller than their prosimian relatives. A 60-million -year-old fossil found in Morocco may be an anthropoid but the conclusion is in dispute. The oldest known anthropoid fossils from Asia were found in Burma (Myanmar). They date to around 37 million years ago and are more monkey-like. [Source: Russel L. Ciochon and Gregg F. Gunnell, Natural History magazine , March 2006]

Primate Characteristics

Primates have relatively large brains for their size but other animals have this same feature and there is nothing particularly extraordinary about it. What is extraordinary if the fetal brain of primates is so much larger than other mammals.

As a rule the larger the brain, the larger the frontal cortex, the part of the brain used by humans for reasoning and higher thought, and the lager the frontal cortex the more intelligent an animal is. Studies have shown that among primates the larger the brain the more intelligent the primate is. Other mammals such as dogs, cats and lions do have particularly large brains.

Primates have color vision. In March 2006, Reuters reported: “Primates may have evolved color vision not to find the ripest, tastiest fruit but rather to detect that telltale blush on someone else's rump, a team at the California Institute of Technology in Pasadena, Calif., reported. The cone structures in the eye that help detect color seem exquisitely tuned to skin tones. "For a hundred years, we've thought that color vision was for finding the right fruit to eat when it was ripe," said Mark Changizi, a neurobiologist and postdoctoral researcher at Caltech who led the study. Instead, Changizi and colleagues report in the current issue of the journal Biology Letters, the system seems adapted especially to find the colors prevalent in primate skins, notably changes due to how much oxygenated hemoglobin is in the blood. [Source: Reuters, March 3, 2006]

The three-cone system can help a primate detect if a potential partner is having a rush of emotion in anticipation of mating and if an enemy's blood has drained out of his face due to fear. "Also ... when you're more oxygenated, you're in better shape," Changizi said. That may be why humans value rosy cheeks, he said. The clincher: Changizi said old-world primates that have the three-cone vision are also all bare-faced and bare-butted. "There's no sense in being able to see the slight color variations in skin if you can't see the skin," Changizi said. "This could connect up with why we're the 'naked ape.' "

Primate Social Behavior

Primates are largely social animals that live in groups and form long term social relationships. Social behavior and group structure can vary depending on the species, group size and even individual population. Things like food supply, the presence of humans, mating dynamics and topography can also have a profound affect on behavior and social organization. Most solitary primates tend to be small and nocturnal.

Some scientists break down primates into two broad categories: 1) “one-male” groups, which revolve around a group in which mating is polygynous and the group is dominated by a single male: and 2) “multi-male/ multi-female” groups, which often contain subgroups and features two important variations: a) fission-fusion societies; and b) harems (effectively one male subgroups).

“One male” systems are characterized by strong competition for females with often violent takeover battles for leadership of the group followed by infanticide and mating by the new male to ensure the females bave offsping related to him not his rival.

Many groups are dominated by females rather than males. Most primate societies in Africa and Asia are made up groups consisting of females that spend their whole lives with a group and males that leave the group they born into around puberty and live on their own or find a new group, which gradually accepts them over time.

Primate Locomotion

Primates employ five major types of locomotion: 1) arboreal quadrupedalism 2) terrestrial quadrupedalism; 3) leaping; 4) hanging and 5) bipedalism.

Arboreal quadrupedalism (using all four limbs in the trees) involves walking, running and bounding in trees, and using a long tail for balance. It is associated with guenons macaques, colobus monkeys, capuchin monkeys, marmosets, tarmarins and bearded sakis. These primates typically have relatively short, flexed limbs of equal length, a narrow thorax, grasping feet, and long fingers and toes.

Terrestrial quadrupedalism (using all four limbs on the ground) is associated with baboons and some macaques. The tail of these primates is reduced in size and their limbs are built mainly for running. The toes and fingers are relatively short. Some of these animals walk on their hind legs for short periods. Bipedalism (standing upright and using two legs for walking) is associated only with humans.

Many primates are excellent leapers. Among the features that make this possible are long, springy hind legs, pelvic bones modified for propulsion, and hands, feet and sometimes tails that are excellent for grabbing branches.

Primate Communication

Primates have a highly diversified communications systems: involving auditory/vocal, tactile, chemical and visual systems. Urine and feces ate important in olfactory communication in a number of species. Touching is very important for many species and often manifests itself in the form of grooming.

Vocalizations seem to be particularly important to forest-dwelling and nocturnal monkeys. The calls are usually associated with territory but also have other uses. Alarm calls have been found that identify different predators.

The question of whether the fear of snakes is learned or inherited was tested with a series of studies at the University of Wisconsin-Madison in the 1980s with laboratory-raised monkeys and wild monkeys. The lab-raised monkeys who had never seen a snake showed no fear when they were exposed to one. However, if they watched wild monkeys — both on video and live — show fear of snakes they quickly adopted the same fear. Evidence that the fear of snake is hardwired into the brain was confirmed by a series of tests in which the lab-raised monkeys were shown a manipulated video of wild monkeys expressing fear of flowers, After watching the video the lab-raised monkey developed no fear of flowers themselves.

Primate Breeding

Primates are slow breeders. They produce few offspring, their gestaion periods are relatively long and their offspring take a long time to mature. Most have only one offspring. Those that don’t have two or three.

Young primates are born relatively helpless and develop relatively slowly. They are often carried around by their mothers for a considerable period of time. Play is an important activity among youngsters in developing social and survival skills.

Primate females like orangutans, chimpanzees and gorillas that raise their offspring live up to 42 percent longer than males. Primate males, such as titis and owl monkeys, that raise their offspring live 15 percent longer than females.

Primate’s and Human-Like Behavior

Darwin noted in his 1872 treatise, “The Expression of Emotions in Man and Animals” that “very many kinds of monkeys, when pleased, utter a reiterated sound, clearly analogous to laughter.”

Monkeys deprived of social companionship develop life-threatening neurosis. Research monkeys forced to live alone in cages often sit in the cages and stare listlessly into space and behave like autistic children.

Researchers from Atlanta’s Emory University have found that monkeys are aware of inequality and injustice. The researchers taught brown capuchin monkeys to receive “tokens” as rewards and trade them for food. They found that the members of the group got along well when cucumbers were the form of trade of food but discovered that monkeys would get jealous when more desirable grapes were given. If one animal received a grape for doing nothing the others were incensed.

Drunken Monkey Hypothesis

Dustin Stephens and Robert Dudley wrote in Natural History magazine, “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. 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

20120528-Alcohol -Caricachupas.JPG
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 owr 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.

Drunken Monkey Hypothesis and Human Alcoholism and Health Problems

drunk Japanese salaryman falls
Dustin Stephens and Robert Dudley wrote in Natural History magazine, “That picture did not change substantially even when modern humans, some 10,000 years ago, learned to control fermentation. As agriculture was developed, barley and wheat became plentiful, which are good for making beer. Archaeological evidence from the same period indicates that wine was also being made. In fact, until industrialization made water filtration practical, alcoholic drinks are thought to have been more widely consumed in many cultures than water was. [Source: Dustin Stephens and Robert Dudley, Natural History magazine, December 2004]

“But the alcoholic drinks of today and the alcoholism that accompanies them are, in evolutionary terms, recent. Yeasts stop making ethanol when its concentration reaches between l0 and 15 percent by weight. Hence drinks made using natural yeasts are limited in alcohol content. Beer and wine made before the invention of chemical distillation probably were no more than 5 percent ethanol.

“The invention of distillation, which had reached Europe in the Middle Ages, radically changed humanity’s relationship with alcohol. Drinks whose ethanol content was much higher than 5 or even 12 percent suddenly became widely available. From the perspective of the drunken monkey hypothesis, the results were predicts a wide availability of potent drink led to alcohol abuse. From the evolutionary perspective taken by Darwinian medicine, alcoholism is one of the "diseases of nutritional excess" that arises from a mismatch between prehistoric and modern environments. Perhaps the most striking example of such a disease is the ongoing epidemic of obesity.

“In 1962, the late geneticistJames Neel predicted that as high-fat, high-calorie Western foods became available to tribal peoples, their rates of obesity, heart disease, and diabetes would sharply increase. Neel’s hypothesis was based on the belief that genes, which had been advantageous in storing and using limited calories, had turned harmful when fats and sugars became readily available. The high rates of diabetes among Pima Indians. Micronesian Nauruans and Australian Aborigines have confirmed his predictions. Neel’s hypothesis, now clearly relevant to human populations in the developed world as well, fits nicely with the drunken monkey hypothesis. The increased alcohol concentration of modern alcoholic drinks played right into a genetically rooted appetite for alcohol. This appetite was present for millions of years and served a valuable survival function for our ancestors as they climbed through the rainforest. And just as with obesity, heart disease, and diabetes, alcoholism has become a risk for anyone with access to the fruits of contemporary culture.

Primates and Humans

A number of primates are endangered and some are close to extinction. Loss of habitat due to deforestation and encroachment by human population have posed the greatest threat. Hunting and capturing primate is also a problem. Sometimes they are killed as pests.

In many developing countries where monkeys live, monkeys are killed for bush meat. Body parts from monkeys are also used as medicines, aphrodisiac ornaments, trophies and bait. Unfortunately some of the most endangered species are also the ones who also valued for the taste of their meat or their aphrodisiac qualities,

Primates are widely used in laboratory experiments, especially is the biomedical and pharmaceutical industry. Some of experiments are quite cruel. Often the animals are kept in very inhumane conditions.

Primates have been given a lot of exposure in National Geographic and BBC documentaries and the work of Jane Goodall and Diane Fossey. Have helped to dispel many myth about the great apes and create an affection for them and other primates.

A number of laws and polices have been established to protect primates. But in places where the most harm is being done, these are difficult to enforce.

Almost a Third of Primates in Danger of Extinction

poacher with baby orangutan

On March 2007, AP reported: “Almost a third of all apes, monkeys and other primates are in danger of going extinct because of rampant destruction of their tropical habitat, the commercial sale of bush meat and the trade in illegal wildlife, a report by the International Primatological Society said. Among the 25 singled out as most endangered are the Miss Waldron's red colobus of Ivory Coast and Ghana, the Golden-headed langur of Vietnam and China's Hainan gibbon, whose numbers have dwindled to 17. The Horton Plains slender loris of Sri Lanka has been sighted just four times since 1937. [Source: ap, October 25, 2007]

Overall, 114 of the world's 394 primate species are classified as threatened with extinction by the World Conservation Union or IUCN. The 25 most endangered primates include 11 from Asia, seven from Africa, four from Madagascar and three from South and Central America. The list includes well-known primates like the Sumatran orangutan of Indonesia and the Cross River gorilla of Cameroon and Nigeria as well as lesser known species such as the Greater bamboo lemur from Madagascar. Conservation International President Russell A. Mittermeier, who also chairs the World Conservation Union's Primate Specialist Group which prepared the report, said, "The situation is worst in Asia, where tropical forest destruction and the hunting and trading of monkeys puts many species at terrible risk. Even newly discovered species are severely threatened from loss of habitat and could soon disappear."

Six species are on the biannual report for the first time, including a recently discovered Indonesian tarsier that has yet to be formally named and the Kipunji from Tanzania, which was discovered in 2003. "Some of the new species we discover are endangered from the get go because they are living in restricted areas," Mittermeier said. "If you find a news species and it's living in an area heavily impacted by habitat destruction and hunting, you recognize it's in trouble."

Habitat loss due to the clearing of tropical forests for agriculture, logging, and the collection of fuel wood continues to be the major factor in the declining number of primates, according to the report. In addition, climate change is altering the habitats of many species, leaving those with small habitat ranges even more vulnerable to extinction, it says. Hunting for subsistence and commercial purposes is another major threat to primates, especially in Africa and Asia. Live capture for the pet trade also poses a serious threat, particularly to Asian species, the report found.

Four primates species on the list from Vietnam have been "decimated" by hunting for their meat and bones, according to Barney Long, a conservation biologist based in Vietnam for WWF Greater Mekong Program. "All four species are close to extinction," Long said, of Delacour's langur, Golden-headed langur, Grey-shanked douc and Tonkin snub-nosed monkey. "The key populations have been stabilized. But there needs to be a lot more law enforcement and work to persuade local communities to support conservation for those numbers to increase."

But the news, the report says, is not all bad. Nine primates from the last report in 2004 were taken off mostly because of bolstered conservation efforts to save their populations. Among them are the Eastern gorilla from Africa, the Black-faced lion tamarin and the Buffy-headed tufted capuchin from Brazil and the Perrier's sifaka from Madagascar. "If you invest in a species in a proper way and do the conservation measures needed, you can reduce risk of extinction," Mittermeier said. "If we had resources, we would be able to take every one of the species off the list in the next five or 10 years."

Image Sources: Wikimedia Commons

Text Sources: National Geographic, Natural History magazine, Smithsonian magazine, Wikipedia, New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, Top Secret Animal Attack Files website, The New Yorker, Time, Newsweek, Reuters, AP, AFP, The Economist, BBC, and various books and other publications.

Last updated November 2012

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