A primate ( PRY-mayt) (from Latin primat-, from primus: "prime, first rank") is a eutherianmammal constituting the taxonomicorderPrimates. Primates arose 85-55 million years ago first from small terrestrial mammals, which adapted to living in the trees of tropical forests: many primate characteristics represent adaptations to life in this challenging environment, including large brains, visual acuity, color vision, altered shoulder girdle, and dextrous hands. Primates range in size from Madame Berthe's mouse lemur, which weighs 30 g (1 oz), to the eastern gorilla, weighing over 200 kg (440 lb). There are 190-448 species of living primates, depending on which classification is used. New primate species continue to be discovered: over 25 species were described in the first decade of the 2000s, and eleven since 2010.
Primates are divided into two distinct suborders (see diagram under History of terminology). The first suborder is called strepsirrhines (from Greek 'twisted-nosed or twisted-nostrilled'), which contains lemurs, galagos, and lorisids. These primates can be found throughout Africa, Madagascar, India, and Southeast Asia. The colloquial names of species ending in -nosed refer to the rhinarium of the primate. The second suborder is called haplorhines, which contains "dry-nosed" primates (from Greek 'simple-nosed') in the tarsier, monkey, and ape clades. The last of these groups includes humans. Simians (the infraorder called Simiiformes from the Greek word simos, meaning 'flat-nosed') refer to monkeys and apes, which can be classified as Old World monkeys and apes under the infraorder of catarrhines (from Greek 'narrow nosed') or as New World monkeys under the infraorder of platyrrhines (from Greek 'flat-nosed'). Forty million years ago, simians from Africa migrated to South America by drifting on debris (presumably), which gave rise to the five families of New World monkeys. The remaining simians (catarrhines) split into apes (Hominoidea) and Old World monkeys (Cercopithecoidea) approximately twenty-five million years ago. Common species that are simians include the (Old World) baboons, macaques, gibbons, and great apes; and the (New World) capuchins, howlers and squirrel monkeys.
Primates have large brains (relative to body size) compared to other mammals, as well as an increased reliance on visual acuity at the expense of the sense of smell, which is the dominant sensory system in most mammals. These features are more developed in monkeys and apes, and noticeably less so in lorises and lemurs. Some primates are trichromats, with three independent channels for conveying color information. Except for apes and humans, primates have tails. Most primates also have opposable thumbs. Many species are sexually dimorphic; differences may include muscle mass, fat distribution, pelvic width, canine tooth size, hair distribution, and coloration. Primates have slower rates of development than other similarly sized mammals, reach maturity later, and have longer lifespans. Depending on the species, adults may live in solitude, in mated pairs, or in groups of up to hundreds of members. Some primates, including gorillas, humans, and baboons, are primarily terrestrial rather than arboreal, but all species have adaptations for climbing trees. Arboreal locomotion techniques used include leaping from tree to tree and swinging between branches of trees (brachiation); terrestrial locomotion techniques include walking on two limbs (bipedalism) and modified walking on four limbs (knuckle-walking).
Primates are among the most social of animals, forming pairs or family groups, uni-male harems, and multi-male/multi-female groups. Non-human primates have at least four types of social systems, many defined by the amount of movement by adolescent females between groups. Most primate species remain at least partly arboreal: the exceptions are humans, some other great apes, and baboons, who left the trees for the ground and now inhabit every continent.
Close interactions between humans and non-human primates (NHPs) can create opportunities for the transmission of zoonotic diseases, especially virus diseases, including herpes, measles, ebola, rabies, and hepatitis. Thousands of non-human primates are used in research around the world because of their psychological and physiological similarity to humans. About 60% of primate species are threatened with extinction. Common threats include deforestation, forest fragmentation, monkey drives, and primate hunting for use in medicines, as pets, and for food. Large-scale tropical forest clearing for agriculture most threatens primates.
History of terminology
The English name "primates" is derived from Old French or Frenchprimat, from a noun use of Latin primat-, from primus ("prime, first rank"). The name was given by Carl Linnaeus because he thought this the "highest" order of animals. The relationships among the different groups of primates were not clearly understood until relatively recently, so the commonly used terms are somewhat confused. For example, "ape" has been used either as an alternative for "monkey" or for any tailless, relatively human-like primate.
Sir Wilfrid Le Gros Clark was one of the primatologists who developed the idea of trends in primate evolution and the methodology of arranging the living members of an order into an "ascending series" leading to humans. Commonly used names for groups of primates such as "prosimians", "monkeys", "lesser apes", and "great apes" reflect this methodology. According to our current understanding of the evolutionary history of the primates, several of these groups are paraphyletic: a paraphyletic group is one which does not include all the descendants of the group's common ancestor.
In contrast with Clark's methodology, modern classifications typically identify (or name) only those groupings that are monophyletic; that is, such a named group includes all the descendants of the group's common ancestor.
The cladogram below shows one possible classification sequence of the living primates: groups that use common (traditional) names are shown on the right.
All groups with scientific names are monophyletic (that is, they are clades), and the sequence of scientific classification reflects the evolutionary history of the related lineages. Groups that are traditionally named are shown on the right; they form an "ascending series" (per Clark, see above), and several groups are paraphyletic:
"prosimians" contain two monophyletic groups (the suborder Strepsirrhini, or lemurs, lorises and allies, as well as the tarsiers of the suborder Haplorhini); it is a paraphyletic grouping because it excludes the Simiiformes, which also are descendants of the common ancestor Primates.
"monkeys" comprise two monophyletic groups, New World monkeys and Old World monkeys, but is paraphyletic because it excludes hominoids, superfamily Hominoidea, also descendants of the common ancestor Simiiformes.
"apes" as a whole, and the "great apes", are paraphyletic if the terms are used such that they exclude humans.
Thus, the members of the two sets of groups, and hence names, do not match, which causes problems in relating scientific names to common (usually traditional) names. Consider the superfamily Hominoidea: In terms of the common names on the right, this group consists of apes and humans and there is no single common name for all the members of the group. One remedy is to create a new common name, in this case "hominoids". Another possibility is to expand the use of one of the traditional names. For example, in his 2005 book, the vertebratepalaeontologist Benton wrote, "The apes, Hominoidea, today include the gibbons and orang-utan ... the gorilla and chimpanzee ... and humans"; thereby Benton was using "apes" to mean "hominoids". In that case, the group heretofore called "apes" must now be identified as the "non-human apes".
As of 2005[update], there is no consensus as to whether to accept traditional (that is, common), but paraphyletic, names or to use monophyletic names only; or to use 'new' common names or adaptations of old ones. Both competing approaches can be found in biological sources, often in the same work, and sometimes by the same author. Thus, Benton defines "apes" to include humans, then he repeatedly uses "ape-like" to mean "like an ape rather than a human"; and when discussing the reaction of others to a new fossil he writes of "claims that Orrorin ... was an ape rather than a human".
Classification of living primates
A 1927 drawing of chimpanzees, a gibbon (top right) and two orangutans (center and bottom center): The chimpanzee in the upper left is brachiating; the orangutan at the bottom center is knuckle-walking.
Homo sapiens is the only living primate species that is fully bipedal
A list of the families of the living primates is given below, together with one possible classification into ranks between order and family. Other classifications are also used. For example, an alternative classification of the living Strepsirrhini divides them into two infraorders, Lemuriformes and Lorisiformes.
Order Primates is part of the clade Euarchontoglires, which is nested within the clade Eutheria of Class Mammalia. Recent molecular genetic research on primates, colugos, and treeshrews has shown that the two species of colugos are more closely related to primates than to treeshrews, even though treeshrews were at one time considered primates. These three orders make up the cladeEuarchonta. The combination of this clade with the clade Glires (composed of Rodentia and Lagomorpha) forms the clade Euarchontoglires. Variously, both Euarchonta and Euarchontoglires are ranked as superorders. Some scientists consider Dermoptera to be a suborder of Primates and use the suborder Euprimates for the "true" primates.
By modern cladistic reckoning, the order Primates is monophyletic. The suborder Strepsirrhini, the "wet-nosed" primates, is generally thought to have split off from the primitive primate line about 63 mya, although earlier dates are also supported. The seven strepsirrhine families are the five related lemur families and the two remaining families that include the lorisids and the galagos. Older classification schemes wrap Lepilemuridae into Lemuridae and Galagidae into Lorisidae, yielding a four-one family distribution instead of five-two as presented here. During the Eocene, most of the northern continents were dominated by two groups, the adapiforms and the omomyids. The former are considered members of Strepsirrhini, but did not have a toothcomb like modern lemurs; recent analysis has demonstrated that Darwinius masillae fits into this grouping. The latter was closely related to tarsiers, monkeys, and apes. How these two groups relate to extant primates is unclear. Omomyids perished about 30 mya, while adapiforms survived until about 10 mya.
According to genetic studies, the lemurs of Madagascar diverged from the lorisoids approximately 75 mya. These studies, as well as chromosomal and molecular evidence, also show that lemurs are more closely related to each other than to other strepsirrhine primates. However, Madagascar split from Africa 160 mya and from India 90 mya. To account for these facts, a founding lemur population of a few individuals is thought to have reached Madagascar from Africa via a single rafting event between 50 and 80 mya. Other colonization options have been suggested, such as multiple colonizations from Africa and India, but none are supported by the genetic and molecular evidence.
Until recently, the aye-aye has been difficult to place within Strepsirrhini. Theories had been proposed that its family, Daubentoniidae, was either a lemuriform primate (meaning its ancestors split from the lemur line more recently than lemurs and lorises split) or a sister group to all the other strepsirrhines. In 2008, the aye-aye family was confirmed to be most closely related to the other Malagasy lemurs, likely having descended from the same ancestral population that colonized the island.
Suborder Haplorhini, the simple-nosed or "dry-nosed" primates, is composed of two sister clades.Prosimian tarsiers in the family Tarsiidae (monotypic in its own infraorder Tarsiiformes), represent the most basal division, originating about 58 mya. The earliest known haplorhine skeleton, that of 55 MA old tarsier-like Archicebus, was found in central China, supporting an already suspected Asian origin for the group. The infraorder Simiiformes (simian primates, consisting of monkeys and apes) emerged about 40 mya, possibly also in Asia; if so, they dispersed across the Tethys Sea from Asia to Africa soon afterwards. There are two simian clades, both parvorders: Catarrhini, which developed in Africa, consisting of Old World monkeys, humans and the other apes, and Platyrrhini, which developed in South America, consisting of New World monkeys. A third clade, which included the eosimiids, developed in Asia, but became extinct millions of years ago.
As in the case of lemurs, the origin of New World monkeys is unclear. Molecular studies of concatenated nuclear sequences have yielded a widely varying estimated date of divergence between platyrrhines and catarrhines, ranging from 33 to 70 mya, while studies based on mitochondrial sequences produce a narrower range of 35 to 43 mya. The anthropoid primates possibly traversed the Atlantic Ocean from Africa to South America during the Eocene by island hopping, facilitated by Atlantic Ocean ridges and a lowered sea level. Alternatively, a single rafting event may explain this transoceanic colonization. Due to continental drift, the Atlantic Ocean was not nearly as wide at the time as it is today. Research suggests that a small 1 kg (2.2 lb) primate could have survived 13 days on a raft of vegetation. Given estimated current and wind speeds, this would have provided enough time to make the voyage between the continents.
Apes and monkeys spread from Africa into Europe and Asia starting in the Miocene. Soon after, the lorises and tarsiers made the same journey. The first hominin fossils were discovered in northern Africa and date back 5-8 mya. Old World monkeys disappeared from Europe about 1.8 mya. Molecular and fossil studies generally show that modern humans originated in Africa 100,000-200,000 years ago.
Although primates are well studied in comparison to other animal groups, several new species have been discovered recently, and genetic tests have revealed previously unrecognised species in known populations. Primate Taxonomy listed about 350 species of primates in 2001; the author, Colin Groves, increased that number to 376 for his contribution to the third edition of Mammal Species of the World (MSW3). However, publications since the taxonomy in MSW3 was compiled in 2003 have pushed the number to 424 species, or 658 including subspecies.
Primate hybrids usually arise in captivity, but there have also been examples in the wild. Hybridization occurs where two species' range overlap to form hybrid zones; hybrids may be created by humans when animals are placed in zoos or due to environmental pressures such as predation. Intergeneric hybridizations, hybrids of different genera, have also been found in the wild. Although they belong to genera that have been distinct for several million years, interbreeding still occurs between the gelada and the hamadryas baboon.
The primate skull has a large, domed cranium, which is particularly prominent in anthropoids. The cranium protects the large brain, a distinguishing characteristic of this group. The endocranial volume (the volume within the skull) is three times greater in humans than in the greatest nonhuman primate, reflecting a larger brain size. The mean endocranial volume is 1,201 cubic centimeters in humans, 469 cm3 in gorillas, 400 cm3 in chimpanzees and 397 cm3 in orangutans. The primary evolutionary trend of primates has been the elaboration of the brain, in particular the neocortex (a part of the cerebral cortex), which is involved with sensory perception, generation of motor commands, spatial reasoning, conscious thought and, in humans, language. While other mammals rely heavily on their sense of smell, the arboreal life of primates has led to a tactile, visually dominant sensory system, a reduction in the olfactory region of the brain and increasingly complex social behavior.
Primates have forward-facing eyes on the front of the skull; binocular vision allows accurate distance perception, useful for the brachiating ancestors of all great apes. A bony ridge above the eye sockets reinforces weaker bones in the face, which are put under strain during chewing. Strepsirrhines have a postorbital bar, a bone around the eye socket, to protect their eyes; in contrast, the higher primates, haplorhines, have evolved fully enclosed sockets.
An 1893 drawing of the hands and feet of various primates
Primates show an evolutionary trend towards a reduced snout. Technically, Old World monkeys are distinguished from New World monkeys by the structure of the nose, and from apes by the arrangement of their teeth. In New World monkeys, the nostrils face sideways; in Old World monkeys, they face downwards. Dental pattern in primates vary considerably; although some have lost most of their incisors, all retain at least one lower incisor. In most strepsirrhines, the lower incisors form a toothcomb, which is used in grooming and sometimes foraging. Old World monkeys have eight premolars, compared with 12 in New World monkeys. The Old World species are divided into apes and monkeys depending on the number of cusps on their molars: monkeys have four, apes have five - although humans may have four or five. The main hominid molar cusp (hypocone) evolved in early primate history, while the cusp of the corresponding primitive lower molar (paraconid) was lost. Prosimians are distinguished by their immobilized upper lips, the moist tip of their noses and forward-facing lower front teeth.
Vervet hindfoot showing fingerprint ridges on the sole
Primates generally have five digits on each limb (pentadactyly), with a characteristic type of keratin fingernail on the end of each finger and toe. The bottom sides of the hands and feet have sensitive pads on the fingertips. Most have opposable thumbs, a characteristic primate feature most developed in humans, though not limited to this order, (opossums and koalas, for example, also have them). Thumbs allow some species to use tools. In primates, the combination of opposing thumbs, short fingernails (rather than claws) and long, inward-closing fingers is a relict of the ancestral practice of gripping branches, and has, in part, allowed some species to develop brachiation (swinging by the arms from tree limb to tree limb) as a significant means of locomotion. Prosimians have clawlike nails on the second toe of each foot, called toilet-claws, which they use for grooming.
Distinct sexual size dimorphism can be seen between the male and female mountain gorilla
Sexual dimorphism is often exhibited in simians, though to a greater degree in Old World species (apes and some monkeys) than New World species. Recent studies involve comparing DNA to examine both the variation in the expression of the dimorphism among primates and the fundamental causes of sexual dimorphism. Primates usually have dimorphism in body mass and canine tooth size along with pelage and skin color. The dimorphism can be attributed to and affected by different factors, including mating system, size, habitat and diet.
Comparative analyses have generated a more complete understanding of the relationship between sexual selection, natural selection, and mating systems in primates. Studies have shown that dimorphism is the product of changes in both male and female traits. Ontogenetic scaling, where relative extension of a common growth trajectory occurs, may give some insight into the relationship between sexual dimorphism and growth patterns. Some evidence from the fossil record suggests that there was convergent evolution of dimorphism, and some extinct hominids probably had greater dimorphism than any living primate.
Like catarrhines, howler monkeys (a family of platyrrhines) show routine trichromatism that has been traced to an evolutionarily recent gene duplication. Howler monkeys are one of the most specialized leaf-eaters of the New World monkeys; fruits are not a major part of their diets, and the type of leaves they prefer to consume (young, nutritive, and digestible) are detectable only by a red-green signal. Field work exploring the dietary preferences of howler monkeys suggests that routine trichromaticism was selected by environment.
Richard Wrangham stated that social systems of primates are best classified by the amount of movement by females occurring between groups. He proposed four categories:
Female transfer systems - females move away from the group in which they were born. Females of a group will not be closely related whereas males will have remained with their natal groups, and this close association may be influential in social behavior. The groups formed are generally quite small. This organization can be seen in chimpanzees, where the males, who are typically related, will cooperate in defense of the group's territory. Among New World Monkeys, spider monkeys and muriquis use this system.
A social huddle of ring-tailed lemurs. The two individuals on the right exposing their white ventral surface are sunning themselves.
Monogamous species - a male-female bond, sometimes accompanied by a juvenile offspring. There is shared responsibility of parental care and territorial defense. The offspring leaves the parents' territory during adolescence.Gibbons essentially use this system, although "monogamy" in this context does not necessarily mean absolute sexual fidelity. These species do not live in larger groups.
Solitary species - often males who defend territories that include the home ranges of several females. This type of organization is found in the prosimians such as the slow loris.Orangutans do not defend their territory but effectively have this organization.
Other systems are known to occur as well. For example, with howler monkeys and gorillas both the males and females typically transfer from their natal group on reaching sexual maturity, resulting in groups in which neither the males nor females are typically related. Some prosimians, colobine monkeys and callitrichid monkeys also use this system.
The transfer of females or males from their native group is likely an adaptation for avoiding inbreeding. An analysis of breeding records of captive primate colonies representing numerous different species indicates that the infant mortality of inbred young is generally higher than that of non-inbred young. This effect of inbreeding on infant mortality is probably largely a result of increased expression of deleterious recessive alleles (see Inbreeding depression).
Primatologist Jane Goodall, who studied in the Gombe Stream National Park, noted fission-fusion societies in chimpanzees. There is fission when the main group splits up to forage during the day, then fusion when the group returns at night to sleep as a group. This social structure can also be observed in the hamadryas baboon,spider monkeys and the bonobo. The gelada has a similar social structure in which many smaller groups come together to form temporary herds of up to 600 monkeys.Humans also form fission-fusion societies. In hunter-gatherer societies, humans form groups which are made up of several individuals that may split up to obtain different resources.
These social systems are affected by three main ecological factors: distribution of resources, group size, and predation. Within a social group there is a balance between cooperation and competition. Cooperative behaviors in many primates species include social grooming (removing skin parasites and cleaning wounds), food sharing, and collective defense against predators or of a territory. Aggressive behaviors often signal competition for food, sleeping sites or mates. Aggression is also used in establishing dominance hierarchies.
Lemurs, lorises, tarsiers, and New World monkeys rely on olfactory signals for many aspects of social and reproductive behavior. Specialized glands are used to mark territories with pheromones, which are detected by the vomeronasal organ; this process forms a large part of the communication behavior of these primates. In Old World monkeys and apes this ability is mostly vestigial, having regressed as trichromatic eyes evolved to become the main sensory organ. Primates also use vocalizations, gestures, and facial expressions to convey psychological state. Facial musculature is very developed in primates, particularly in monkeys and apes, allowing for complex facial communication. Like humans, chimpanzees can distinguish the faces of familiar and unfamiliar individuals. Hand and arm gestures are also important forms of communication for great apes and a single gesture can have multiple functions.
The Philippine tarsier, has a high-frequency limit of auditory sensitivity of approximately 91 kHz with a dominant frequency of 70 kHz. Such values are among the highest recorded for any terrestrial mammal, and a relatively extreme example of ultrasonic communication. For Philippine tarsiers, ultrasonic vocalizations might represent a private channel of communication that subverts detection by predators, prey and competitors, enhances energetic efficiency, or improves detection against low-frequency background noise. Male howler monkeys are among the loudest land mammals and their roars can be heard up to 4.8 km (3.0 mi). Roars are produced by modified larynx and enlarged hyoid bone which contains an air sac. These calls are thought to relate to intergroup spacing and territorial protection as well as possibly mate-guarding. The vervet monkey gives a distinct alarm call for each of at least four different predators, and the reactions of other monkeys vary according to the call. For example, if an alarm call signals a python, the monkeys climb into the trees, whereas the eagle alarm causes monkeys to seek a hiding place on the ground. Many non-human primates have the vocal anatomy to produce human speech but lack the proper brain wiring. Vowel-like vocal patterns have been recorded in baboons which has implications for the origin of speech in humans.
The time range for the evolution of human language and/or its anatomical prerequisites extends, at least in principle, from the phylogenetic divergence of Homo (2.3 to 2.4 million years ago) from Pan (5 to 6 million years ago) to the emergence of full behavioral modernity some 50,000-150,000 years ago. Few dispute that Australopithecus probably lacked vocal communication significantly more sophisticated than that of great apes in general.
Primates have slower rates of development than other mammals. All primate infants are breastfed by their mothers (with the exception of some human cultures and various zoo raised primates which are fed formula) and rely on them for grooming and transportation. In some species, infants are protected and transported by males in the group, particularly males who may be their fathers. Other relatives of the infant, such as siblings and aunts, may participate in its care as well. Most primate mothers cease ovulation while breastfeeding an infant; once the infant is weaned the mother can reproduce again. This often leads to weaning conflict with infants who attempt to continue breastfeeding.
Infanticide is common in polygynous species such as gray langurs and gorillas. Adult males may kill dependent offspring that are not theirs so the female will return to estrus and thus they can sire offspring of their own. Social monogamy in some species may have evolved to combat this behavior.Promiscuity may also lessen the risk of infanticide since paternity becomes uncertain.
Primates have a longer juvenile period between weaning and sexual maturity than other mammals of similar size. Some primates such as galagos and new world monkeys use tree-holes for nesting, and park juveniles in leafy patches while foraging. Other primates follow a strategy of "riding", i.e. carrying individuals on the body while feeding. Adults may construct or use nesting sites, sometimes accompanied by juveniles, for the purpose of resting, a behavior which has developed secondarily in the great apes. During the juvenile period, primates are more susceptible than adults to predation and starvation; they gain experience in feeding and avoiding predators during this time. They learn social and fighting skills, often through playing. Primates, especially females, have longer lifespans than other similarly sized mammals, this may be partially due to their slower metabolisms. Late in life, female catarrhine primates appear to undergo a cessation of reproductive function known as menopause; other groups are less studied.
A mouse lemur holds a cut piece of fruit in its hands and eats
Primates exploit a variety of food sources. It has been said that many characteristics of modern primates, including humans, derive from an early ancestor's practice of taking most of its food from the tropical canopy. Most primates include fruit in their diets to obtain easily digested nutrients including carbohydrates and lipids for energy. Primates in the suborder Strepsirrhini (non-tarsier prosimians) are able to synthesize vitamin C, like most other mammals, while primates of the suborder Haplorrhini (tarsiers, monkeys and apes) have lost this ability, and require the vitamin in their diet.
Many primates have anatomical specializations that enable them to exploit particular foods, such as fruit, leaves, gum or insects. For example, leaf eaters such as howler monkeys, black-and-white colobuses and sportive lemurs have extended digestive tracts which enable them to absorb nutrients from leaves that can be difficult to digest.Marmosets, which are gum eaters, have strong incisor teeth, enabling them to open tree bark to get to the gum, and claws rather than nails, enabling them to cling to trees while feeding. The aye-aye combines rodent-like teeth with a long, thin middle finger to fill the same ecological niche as a woodpecker. It taps on trees to find insect larvae, then gnaws holes in the wood and inserts its elongated middle finger to pull the larvae out. Some species have additional specializations. For example, the grey-cheeked mangabey has thick enamel on its teeth, enabling it to open hard fruits and seeds that other monkeys cannot. The gelada is the only primate species that feeds primarily on grass.
Humans have traditionally hunted prey for subsistence.
Until the development of agriculture approximately 10,000 years ago, Homo sapiens employed a hunter-gatherer method as their sole means of food collection. This involved combining stationary food sources (such as fruits, grains, tubers, and mushrooms, insect larvae and aquatic mollusks) with wild game, which must be hunted and killed in order to be consumed. It has been proposed that humans have used fire to prepare and cook food since the time of Homo erectus. Around ten thousand years ago, humans developed agriculture, which substantially altered their diet. This change in diet may also have altered human biology; with the spread of dairy farming providing a new and rich source of food, leading to the evolution of the ability to digest lactose in some adults.
Predators of primates include various species of carnivorans, birds of prey, reptiles, and other primates. Even gorillas have been recorded as prey. Predators of primates have diverse hunting strategies and as such, primates have evolved several different antipredator adaptations including crypsis, alarm calls and mobbing. Several species have separate alarm calls for different predators such as air-borne or ground-dwelling predators. Predation may have shaped group size in primates as species exposed to higher predation pressures appear to live in larger groups.
Intelligence and cognition
Primates have advanced cognitive abilities: some make tools and use them to acquire food and for social displays; some can perform tasks requiring cooperation, influence and rank; they are status conscious, manipulative and capable of deception; they can recognise kin and conspecifics; and they can learn to use symbols and understand aspects of human language including some relational syntax and concepts of number and numerical sequence. Research in primate cognition explores problem solving, memory, social interaction, a theory of mind, and numerical, spatial, and abstract concepts. Comparative studies show a trend towards higher intelligence going from prosimians to New World monkeys to Old World monkeys, and significantly higher average cognitive abilities in the great apes. However, there is a great deal of variation in each group (e.g., among New World monkeys, both spider and capuchin monkeys have scored highly by some measures), as well as in the results of different studies.
In 1960, Jane Goodall observed a chimpanzee poking pieces of grass into a termite mound and then raising the grass to his mouth. After he left, Goodall approached the mound and repeated the behaviour because she was unsure what the chimpanzee was doing. She found that the termites bit onto the grass with their jaws. The chimpanzee had been using the grass as a tool to "fish" or "dip" for termites. There are more limited reports of the closely related bonobo using tools in the wild; it has been claimed they rarely use tools in the wild although they use tools as readily as chimpanzees when in captivity. It has been reported that females, both chimpanzee and bonobo, use tools more avidly than males.Orangutans in Borneo scoop catfish out of small ponds. Anthropologist Anne Russon saw several animals on these forested islands learn on their own to jab at catfish with sticks, so that the panicked prey would flop out of ponds and into the orangutan's waiting hands There are few reports of gorillas using tools in the wild. An adult female western lowland gorilla used a branch as a walking stick apparently to test water depth and to aid her in crossing a pool of water. Another adult female used a detached trunk from a small shrub as a stabilizer during food gathering, and another used a log as a bridge.
The black-striped capuchin was the first non-ape primate for which tool use was documented in the wild; individuals were observed cracking nuts by placing them on a stone anvil and hitting them with another large stone. In Thailand and Myanmar, crab-eating macaques use stone tools to open nuts, oysters and other bivalves, and various types of sea snails. Chacma baboons use stones as weapons; stoning by these baboons is done from the rocky walls of the canyon where they sleep and retreat to when they are threatened. Stones are lifted with one hand and dropped over the side whereupon they tumble down the side of the cliff or fall directly to the canyon floor.
Although they have not been observed to use tools in the wild, lemurs in controlled settings have been shown to be capable of understanding the functional properties of the objects they had been trained to use as tools, performing as well as tool-using haplorhines.
Tool manufacture is much rarer than simple tool use and probably represents higher cognitive functioning. Soon after her initial discovery of tool use, Goodall observed other chimpanzees picking up leafy twigs, stripping off the leaves and using the stems to fish for insects. This change of a leafy twig into a tool was a major discovery. Prior to this, scientists thought that only humans manufactured and used tools, and that this ability was what separated humans from other animals. Chimpanzees have also been observed making "sponges" out of leaves and moss that suck up water. Sumatran orangutans have been observed making and using tools. They will break off a tree branch that is about 30 cm long, snap off the twigs, fray one end and then use the stick to dig in tree holes for termites. In the wild, mandrills have been observed to clean their ears with modified tools. Scientists filmed a large male mandrill at Chester Zoo (UK) stripping down a twig, apparently to make it narrower, and then using the modified stick to scrape dirt from underneath its toenails. Captive gorillas have made a variety of tools.
Many species of NHP are kept as pets by humans, the Allied Effort to Save Other Primates (AESOP) estimates that around 15,000 NHPs live as exotic pets in the United States. The expanding Chinese middle class has increased demand for NHPs as exotic pets in recent years. Although NHP import for the pet trade was banned in the U.S. in 1975, smuggling still occurs along the United States - Mexico border, with prices ranging from US$3000 for monkeys to $30,000 for apes.
NHPs are kept in zoos around the globe. Historically, zoos were primarily a form of entertainment, but more recently have shifted their focus towards conservation, education and research. GAP does not insist that all NHPs should be released from zoos, primarily because captive-born primates lack the knowledge and experience to survive in the wild if released.
In 2005, GAP reported that 1,280 of the 3,100 NHPs living in captivity in the United States were used for experiments. In 2004, the European Union used around 10,000 NHPs in such experiments; in 2005 in Great Britain, 4,652 experiments were conducted on 3,115 NHPs. Governments of many nations have strict care requirements of NHPs kept in captivity. In the US, federal guidelines extensively regulate aspects of NHP housing, feeding, enrichment, and breeding. European groups such as the European Coalition to End Animal Experiments are seeking a ban on all NHP use in experiments as part of the European Union's review of animal testing legislation.
The International Union for Conservation of Nature (IUCN) lists more than a third of primates as critically endangered or vulnerable. About 60% of primate species are threatened with extinction, including: 87% of species in Madagascar, 73% in Asia, 37% in Africa, and 36% in South and Central America. Additionally, 75% of primate species have decreasing populations. Trade is regulated, as all species are listed by CITES in Appendix II, except 50 species and subspecies listed in Appendix I, which gain full protection from trade.
Common threats to primate species include deforestation, forest fragmentation, monkey drives (resulting from primate crop raiding), and primate hunting for use in medicines, as pets, and for food. Large-scale tropical forest clearing is widely regarded as the process that most threatens primates. More than 90% of primate species occur in tropical forests. The main cause of forest loss is clearing for agriculture, although commercial logging, subsistence harvesting of timber, mining, and dam construction also contribute to tropical forest destruction. In Indonesia large areas of lowland forest have been cleared to increase palm oil production, and one analysis of satellite imagery concluded that during 1998 and 1999 there was a loss of 1,000 Sumatran orangutans per year in the Leuser Ecosystem alone.
Primates with a large body size (over 5 kg) are at increased extinction risk due to their greater profitability to poachers compared to smaller primates. They reach sexual maturity later and have a longer period between births. Populations therefore recover more slowly after being depleted by poaching or the pet trade. Data for some African cities show that half of all protein consumed in urban areas comes from the bushmeat trade. Endangered primates such as guenons and the drill are hunted at levels that far exceed sustainable levels. This is due to their large body size, ease of transport and profitability per animal. As farming encroaches on forest habitats, primates feed on the crops, causing the farmers large economic losses. Primate crop raiding gives locals a negative impression of primates, hindering conservation efforts.
Madagascar, home to five endemic primate families, has experienced the greatest extinction of the recent past; since human settlement 1,500 years ago, at least eight classes and fifteen of the larger species have become extinct due to hunting and habitat destruction. Among the primates wiped out were Archaeoindris (a lemur larger than a silverback gorilla) and the families Palaeopropithecidae and Archaeolemuridae.
In Asia, Hinduism, Buddhism, and Islam prohibit eating primate meat; however, primates are still hunted for food. Some smaller traditional religions allow the consumption of primate meat. The pet trade and traditional medicine also increase demand for illegal hunting. The rhesus macaque, a model organism, was protected after excessive trapping threatened its numbers in the 1960s; the program was so effective that they are now viewed as a pest throughout their range.
In Central and South America forest fragmentation and hunting are the two main problems for primates. Large tracts of forest are now rare in Central America. This increases the amount of forest vulnerable to edge effects such as farmland encroachment, lower levels of humidity and a change in plant life. Movement restriction results in a greater amount of inbreeding, which can cause deleterious effects leading to a population bottleneck, whereby a significant percentage of the population is lost.
^ abAlthough the monophyletic relationship between lemurs and lorisoids is widely accepted, their clade name is not. The term "lemuriform" is used here because it derives from one popular taxonomy that clumps the clade of toothcombed primates into one infraorder and the extinct, non-toothcombed adapiforms into another, both within the suborder Strepsirrhini. However, another popular alternative taxonomy places the lorisoids in their own infraorder, Lorisiformes.
^Article 6: Everyone has the right to recognition everywhere as a person before the law.
^ abRylands, A. B. & Mittermeier, R. A. (2009). "The Diversity of the New World Primates (Platyrrhini)". In Garber, P. A.; Estrada, A.; Bicca-Marques, J. C.; Heymann, E. W. & Strier, K. B. (eds.). South American Primates: Comparative Perspectives in the Study of Behavior, Ecology, and Conservation. Springer. ISBN978-0-387-78704-6.
^Linnaeus, C. (1758). Sistema naturae per regna tria Naturae, secundum classes, ordines, genera, species, cum characteribus differentiis, synonimis locis. Tomus I. Impensis direct. Laurentii Salvii, Holmia. pp. 20-32.
^Linnaeus, C. (1735). Sistema naturae sive regna tria Naturae systematice proposita per classes, ordines, genera, & species. apud Theodorum Haak, Lugduni Batavorum. pp. s.p.
^Blainville, H. (1839). "Nouvelle classification des Mammifères". Annales Françaises et Etrangères d'Anatomie et de Physiologie Appliquées à la Médicine et à l'Histoire Naturelle, 3. pp. 268-269.
^Thorington, R. W. & Anderson, S. (1984). "Primates". In Anderson, S. & Jones, J. K. (eds.). Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons. pp. 187-217. ISBN978-0-471-08493-8.
^McKenna, M. C. & Bell, S. K. (1997). Classification of Mammals: Above the species level. New York: Columbia University Press. p. 631. ISBN0-231-11013-8.
^Jameson, Natalie M.; Hou, Zhuo-Cheng; Sterner, Kirstin N.; Weckle, Amy; Goodman, Morris; Steiper, Michael E.; Wildman, Derek E. (September 2011). "Genomic data reject the hypothesis of a prosimian primate clade". Journal of Human Evolution. 61 (3): 295-305. doi:10.1016/j.jhevol.2011.04.004. ISSN0047-2484. PMID21620437.
^ abcdHartwig, W. (2007). "Primate Evolution". In Campbell, C.; Fuentes, A.; MacKinnon, K.; Panger, M.; Bearder, S. (eds.). Primates in Perspective. Oxford University Press. pp. 13-17. ISBN978-0-19-517133-4.
^Sugawara, K. (January 1979). "Sociological study of a wild group of hybrid baboons between Papio anubis and P. hamadryas in the Awash Valley, Ethiopia". Primates. 20 (1): 21-56. doi:10.1007/BF02373827.
^Jolly, C. J.; Woolley-Barker, Tamsin; et al. (1997). "Intergeneric Hybrid Baboons". International Journal of Primatology. 18 (4): 597-627. doi:10.1023/A:1026367307470.
^Russo GA, Young JW (November 2011). "Tail growth tracks the ontogeny of prehensile tail use in capuchin monkeys (Cebus albifrons and C. apella)". American Journal of Physical Anthropology. 146 (3): 465-73. doi:10.1002/ajpa.21617. PMID21953012.
^Ralls, K. (1976). "Mammals in Which Females are Larger Than Males". The Quarterly Review of Biology. 51 (2): 245-76. doi:10.1086/409310. PMID785524.
^Lindstedtand & Boyce; Boyce, Mark S. (July 1985). "Seasonality, Fasting Endurance, and Body Size in Mammals". The American Naturalist. 125 (6): 873. doi:10.1086/284385.
^Thorén, Sandra; Lindenfors, Patrik; Kappeler, Peter M. (2006). "Phylogenetic analyses of dimorphism in primates: Evidence for stronger selection on canine size than on body size". American Journal of Physical Anthropology. 130 (1): 50-59. doi:10.1002/ajpa.20321. ISSN0002-9483. PMID16345072.
^Frisch, J. E. (1963). "Sex-differences in the canines of the gibbon (Hylobates lar)". Primates. 4 (2): 1-10. doi:10.1007/BF01659148.
^ abCheverud, J. M.; Dow, M. M.; Leutenegger, W. (November 1985). "The quantitative assessment of phylogenetic constraints in comparative analyses: Sexual dimorphism in body weight among primates". Evolution. 39 (6): 1335-1351. doi:10.2307/2408790. JSTOR2408790. PMID28564267.
^Leutenegger, W.; Cheverud, J. M. (1982). "Correlates of sexual dimorphism in primates: Ecological and size variables". International Journal of Primatology. 3 (4): 387-402. doi:10.1007/BF02693740.
^ abcdeSussman, R. W. (2003). Primate Ecology and Social Structure, Volume 2: New World Monkeys (Revised First ed.). Needham Heights, MA: Pearson Custom Publishing & Prentice Hall. pp. 77-80, 132-133, 141-143. ISBN0-536-74364-9.
^Glazier, S. D.; Flowerday, C. A. (2003). Selected Readings in the Anthropology of Religion: Theoretical and Methodological Essays. Greenwood Publishing Group. p. 53. ISBN9780313300905.
^ abSurridge, A. K. & D. Osorio (2003). "Evolution and selection of trichromatic vision in primates". Trends in Ecology and Evolution. 18 (4): 198-205. doi:10.1016/S0169-5347(03)00012-0.
^Lucas, P. W.; Dominy, N. J.; Riba-Hernandez, P.; Stoner, K. E.; Yamashita, N.; Loría-Calderón, E.; Petersen-Pereira, W.; Rojas-Durán, Y.; Salas-Pena, R.; Solis-Madrigal, S.; Osorio, D.; Darvell, B. W. (2003). "Evolution and function of routine trichromatic vision in primates". Evolution. 57 (11): 2636-43. doi:10.1554/03-168. PMID14686538.
^Goldberg, T. L.; Wrangham, R. W. (September 1997). "Genetic correlates of social behavior in wild chimpanzees: evidence from mitochondrial DNA". Animal Behaviour. 54 (3): 559-70. doi:10.1006/anbe.1996.0450. PMID9299041.
^Fiore, A. D. & Campbell, C. J. (2007). "The Atelines". In Campbell, C. J.; Fuentes, A.; MacKinnon, K. C.; Panger, M. & Bearder, S. K. (eds.). Primates in Perspective. Oxford University Press. p. 175. ISBN978-0-19-517133-4.
^Bartlett, T. Q. (2007). "The Hylobatidae". In Campbell, C. J.; Fuentes, A.; MacKinnon, K. C.; Panger, M.; Bearder, S. K. (eds.). Primates in Perspective. Oxford University Press. p. 283. ISBN978-0-19-517133-4.
^Knott, C. D. & Kahlenberg, S. M. (2007). "Orangutans in Perspective". In Campbell, C. J.; Fuentes, A.; MacKinnon, K. C.; Panger, M. & Bearder, S. K. (eds.). Primates in Perspective. Oxford University Press. p. 294. ISBN978-0-19-517133-4.
^Watts D. P. (1996). "Comparative socio-ecology of gorillas". In McGrew W. C.; Marchant L. F.; Nishida, T. (eds.). Great Ape Societies. Cambridge (England: Cambridge Univ Press. pp. 16-28. ISBN978-0521555364.
^ abCharpentier MJ, Widdig A, Alberts SC (December 2007). "Inbreeding depression in non-human primates: a historical review of methods used and empirical data". American Journal of Primatology. 69 (12): 1370-86. doi:10.1002/ajp.20445. PMID17486606.
^ abPough, F. W.; Janis, C. M.; Heiser, J. B. (2005) . "Primate Societies". Vertebrate Life (7th ed.). Pearson. pp. 621-623. ISBN0-13-127836-3.
^Smuts, B.B., Cheney, D.L. Seyfarth, R.M., Wrangham, R.W., & Struhsaker, T.T. (Eds.) (1987). Primate Societies. Chicago: University of Chicago Press for articles on the structure and function of various primate societies.
^Shultz, S. & Thomsett, S. (2007). "Interactions between African Crowned Eagles and Their Prey Community". In McGraw, W.; Zuberbuhler, K. & Noe, R. (eds.). Monkeys of Tai Forest, An African Primate Community. Cambridge University Press. p. 181. ISBN978-0-521-81633-5.
^ abBshary, R. (2007). "Interactions between Red Colobus Monkeys and Chimpanzees". In McGraw, W.; Zuberbuhler, K.; Noe, R. (eds.). Monkeys of Tai Forest, An African Primate Community. Cambridge University Press. pp. 155-170. ISBN978-0-521-81633-5.
^Stanford, C. (1998). Chimpanzee and Red Colobus : the ecology of predator and prey. Harvard University Press. pp. 130-138, 233. ISBN0-674-00722-0.
^ abBoinski, S. (2000). "Social Manipulation Within and Between Troops Mediates Primate Group Movement". In Boinski, S.; Garber, P. (eds.). On the Move : how and why animals travel in groups. University of Chicago Press. pp. 447-448. ISBN0-226-06340-2.
^da Cunha, R. G. T.; Byrne, R. (2006). "Roars of Black Howler Monkeys (Alouatta caraya): Evidence for a Function in Inter-Group Spacing". Behaviour. 143 (10): 1169-1199. doi:10.1163/156853906778691568. JSTOR4536401.
^Milliken, G. W.; Ward, J. P.; Erickson, C. J. (1991). "Independent digit control in foraging by the aye-aye (Daubentonia madagascariensis)". Folia Primatologica. 56 (4): 219-224. doi:10.1159/000156551. PMID1937286.
^Surbeck, M; Fowler, A; Deimel, C; Hohmann, G (2008). "Evidence for the consumption of arboreal, diurnal primates by bonobos (Pan paniscus)". American Journal of Primatology. 71 (2): 171-4. doi:10.1002/ajp.20634. PMID19058132.
^Holden C, Mace R (October 1997). "Phylogenetic analysis of the evolution of lactose digestion in adults". Hum. Biol. 69 (5): 605-28. PMID9299882.
^Fichtel, Claudia (2012). "Predation". In Mitani, John C.; Call, Josep; Kappeler, Peter M.; Palombit, Ryne A.; Silk, Joan B (eds.). The Evolution of Primate Societies. University of Chicago Press. pp. 169-84. ISBN978-0-226-53172-4.
^Westergaard, G. C.; Lundquist, A. L.; et al. (1998). "Why some capuchin monkeys (Cebus apella) use probing tools (and others do not)". Journal of Comparative Psychology. 112 (2): 207-211. doi:10.1037/0735-7036.112.2.207. PMID9642788.
^Fujita, K.; Watanabe, K.; Widarto, T. H.; Suryobroto, B. (1997). "Discrimination of macaques by macaques: The case of sulawesi species". Primates. 38 (3): 233-245. doi:10.1007/BF02381612.
^Call, J. (2001). "Object permanence in orangutans (Pongo pygmaeus), chimpanzees (Pan troglodytes), and children (Homo sapiens)". Journal of Comparative Psychology. 115 (2): 159-171. doi:10.1037/0735-7036.115.2.159. PMID11459163.
^Itakura, S.; Tanaka, M. (June 1998). "Use of experimenter-given cues during object-choice tasks by chimpanzees (Pan troglodytes), an orangutan (Pongo pygmaeus), and human infants (Homo sapiens)". Journal of Comparative Psychology. 112 (2): 119-126. doi:10.1037/0735-7036.112.2.119. PMID9642782.
^Fragaszy, D.; Izar, P.; Visalberghi, E.; Ottoni, E.B.; de Oliveira, M.G. (2004). "Wild capuchin monkeys (Cebus libidinosus) use anvils and stone pounding tools". American Journal of Primatology. 64 (4): 359-366. doi:10.1002/ajp.20085. PMID15580579.
^Gumert, M.D.; Kluck, M.; Malaivijitnond, S. (2009). "The physical characteristics and usage patterns of stone axe and pounding hammers used by long-tailed macaques in the Andaman Sea region of Thailand". American Journal of Primatology. 71 (7): 594-608. doi:10.1002/ajp.20694. PMID19405083.
^Chapman, C. & Russo, S. (2007). "Primate Seed Dispersal". In Campbell, C. J.; Fuentes, A.; MacKinnon, K. C.; Panger, M. & Bearder, S. K. (eds.). Primates in Perspective. Oxford University Press. p. 510. ISBN978-0-19-517133-4.
^Long, Y. C.; Kirkpatrick, R. C.; Zhong, T.; Xiao, L. (April 1994). "Report on the distribution, population, and ecology of the Yunnan snub-nosed monkey (Rhinopithecus bieti)". Primates. 35 (2): 241-250. doi:10.1007/BF02382060.
^Stammbach, E. (1987). "Desert, Forest, and Montane Baboons: Multilevel-Societies". In Smuts, B; Cheney, D; Seyfarth, R; Wrangham, R; Struhsaker, T. (eds.). Primate Societies. The University of Chicago Press. pp. 112-120. ISBN978-0226767161.
^Wolfe, L. D. & Fuentes, A. (2007). "Ethnoprimatology". In Campbell, C. J.; Fuentes, A.; MacKinnon, K. C.; Panger, M. & Bearder, S. K. (eds.). Primates in Perspective. Oxford University Press. p. 692. ISBN978-0-19-517133-4.
^Conlee, K. M.; Hoffeld, E. H.; Stephens, M. L. (2004). "A Demographic Analysis of Primate Research in the United States". Alternatives to Laboratory Animals. 32 (Sup 1): 315-322. doi:10.1177/026119290403201s52. PMID23577480.
^ abMittermeier, R. A. & Cheney, D. L. (1987). "Conservation of primates and their habitats". In Smuts, B. B.; Cheney, D. L.; Seyfarth, R. M.; Wrangham, R. W. & Struhsaker, T. T. (eds.). Primate Societies. Chicago: University of Chicago Press. pp. 477-490.
^ abcdCowlishaw, G. & Dunbar, R. (2000). Primate Conservation Biology. Chicago: University of Chicago Press. ISBN978-0-226-11637-2.
^Van Schaik, C. P.; Monk, K. A.; Robertson, J. M. Y. (2001). "Dramatic decline in orangutan numbers in the Leuser Ecosystem, northern Sumatra". Oryx. 35 (1): 14-25. doi:10.1046/j.1365-3008.2001.00150.x.
^Hill, C. M. (1997). "Crop-raiding by wild vertebrates: The farmer's perspective in an agricultural community in western Uganda". International Journal of Pest Management. 43 (1): 77-84. doi:10.1080/096708797229022.
^Hill, C. M. (2002). "Primate conservation and local communities: Ethical issues and debates". American Anthropologist. 104 (4): 1184-1194. doi:10.1525/aa.2002.104.4.1184.
^Kumara, H. N.; Singh, M. (October 2004). "Distribution and abundance of primates in rainforests of the Western Ghats, Karnataka, India and the conservation of Macaca silenus". International Journal of Primatology. 25 (5): 1001-1018. doi:10.1023/B:IJOP.0000043348.06255.7f.
^O'Brien, T. G.; Kinnaird, M. F.; Nurcahyo, A.; Iqbal, M.; Rusmanto, M. (April 2004). "Abundance and distribution of sympatric gibbons in a threatened Sumatran rain forest". International Journal of Primatology. 25 (2): 267-284. doi:10.1023/B:IJOP.0000019152.83883.1c.
^Estrada, A.; Coates-Estrada, R.; Meritt, D. (September 1994). "Non-flying mammals and landscape changes in the tropical forest region of Los Tuxtlas, Mexico". Ecography. 17 (3): 229-241. doi:10.1111/j.1600-0587.1994.tb00098.x.
^Turner, I. M. (1996). "Species loss in fragments of tropical rain forest: a review of the evidence". Journal of Applied Ecology. 33 (2): 200-209. doi:10.2307/2404743. JSTOR2404743.
^Chiarello, A.G. (2003). "Primates of the Brazilian Atlantic forest: the influence of forest fragmentation on survival". In Marsh, L. K. (ed.). Primates in Fragments: Ecology and Conservation. New York: Kluwer Academic/Plenum Publishers. pp. 99-121. ISBN978-0-306-47696-9.
^Pope, T.R. (1996). "Socioecology, population fragmentation, and patterns of genetic loss in endangered primates". In Avise, J.; Hamrick, J. (eds.). Conservation Genetics: Case Histories from Nature. Norwell: Kluwer Academic Publishers. pp. 119-159. ISBN978-0-412-05581-2.
^Oates, J. F.; Abedi-Lartey, M.; McGraw, W. S.; Struhsaker, T. T.; Whitesides, G. H. (October 2000). "Extinction of a West African Red Colobus Monkey". Conservation Biology. 14 (5): 1526-1532. doi:10.1046/j.1523-1739.2000.99230.x.
^McGraw, W. S. (June 2005). "Update on the Search for Miss Waldron's Red Colobus Monkey". International Journal of Primatology. 26 (3): 605-619. doi:10.1007/s10764-005-4368-9.
Hartwig, W. (2011). "Chapter 3: Primate evolution". In Campbell, C. J.; Fuentes, A.; MacKinnon, K. C.; Bearder, S. K.; Stumpf, R. M (eds.). Primates in Perspective (2nd ed.). Oxford University Press. pp. 19-31. ISBN978-0-19-539043-8.