Primates have largebrains (relative to body size) compared to other mammals, as well as an increased reliance onvisual acuity at the expense of thesense 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, includinggorillas,humans andbaboons, are primarily ground-dwelling 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 twohindlimbs (bipedalism) and modified walking on four limbs (quadrupedalism) viaknuckle-walking.
Primates are among the mostsocial of all animals, forming pairs or family groups, uni-male harems, and multi-male/multi-female groups. Non-human primates have at least four types ofsocial systems, many defined by the amount of movement by adolescent females between groups. Primates have slower rates of development than other similarly sized mammals, reach maturity later, and have longer lifespans. Primates are also the mostcognitively advanced animals, with humans (genusHomo) capable of creating complexlanguages and sophisticatedcivilizations, and non-human primates are recorded touse tools. They may communicate using facial and hand gestures, smells and vocalizations.
Close interactions between humans and non-human primates (NHPs) can create opportunities for the transmission ofzoonotic diseases, especially virus diseases includingherpes,measles,ebola,rabies andhepatitis. 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 includedeforestation,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.
Etymology
The English nameprimates is derived fromOld French or Frenchprimat, from a noun use of Latinprimat-, fromprimus ('prime, first rank').[3] The name was given byCarl Linnaeus because he thought this the "highest" order of animals.[4] 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 formonkey or for any tailless, relatively human-like primate.[5][6]
SirWilfrid Le Gros Clark was one of theprimatologists 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.[7] Commonly used names for groups of primates such asprosimians,monkeys,lesser apes, andgreat apes reflect this methodology. According to our current understanding of the evolutionary history of the primates, several of these groups areparaphyletic, or rather they do not include all the descendants of a common ancestor.[8]
In contrast with Clark's methodology, modern classifications typically identify (or name) only those groupings that aremonophyletic; that is, such a named group includesall the descendants of the group's common ancestor.[9]
All groups with scientific names areclades, or monophyletic groups, 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 thegreat 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 casehominoids. Another possibility is to expand the use of one of the traditional names. For example, in his 2005 book, thevertebratepalaeontologist Benton wrote, "The apes, Hominoidea, today include thegibbons andorangutan ... thegorilla andchimpanzee ... andhumans";[10] thereby Benton was usingapes to mean hominoids. In that case, the group heretofore calledapes must now be identified as the non-human apes.
As of 2021[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 definesapes to include humans, then he repeatedly usesape-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 thatOrrorin ... was an ape rather than a human".[11]
Thecladogram below shows one possible classification sequence of the living primates:[18][19] groups that use common (traditional) names are shown on the right.
Order Primates is part of the cladeEuarchontoglires, which is nested within the cladeEutheria of ClassMammalia. Recent molecular genetic research on primates,colugos, andtreeshrews has shown that the two species of colugos are more closely related to primates than to treeshrews,[23] even though treeshrews were at one time considered primates.[24] These three orders make up thecladeEuarchonta. The combination of this clade with the cladeGlires (composed ofRodentia andLagomorpha) 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.[25]
By moderncladistic reckoning, the order Primates ismonophyletic. The suborderStrepsirrhini, the "wet-nosed" primates, is generally thought to have split off from the primitive primate line about 63 mya,[39] although earlier dates are also supported.[40] The seven strepsirrhine families are the five relatedlemur families and the two remaining families that include thelorisids and thegalagos.[1][41] Older classification schemes wrapLepilemuridae intoLemuridae andGalagidae intoLorisidae, yielding a four-one family distribution instead of five-two as presented here.[1] During theEocene, most of the northern continents were dominated by two groups, theadapiforms and theomomyids.[42][43] The former are considered members of Strepsirrhini, but did not have atoothcomb like modern lemurs; recent analysis has demonstrated thatDarwinius masillae fits into this grouping.[44] 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,[43] while adapiforms survived until about 10 mya.[45]
According to genetic studies, the lemurs of Madagascar diverged from the lorisoids approximately 75 mya.[40] 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.[40][46] However, Madagascar split from Africa 160 mya and from India 90 mya.[47] To account for these facts, a founding lemur population of a few individuals is thought to have reached Madagascar from Africa via a singlerafting event between 50 and 80 mya.[40][46][47] Other colonization options have been suggested, such as multiple colonizations from Africa and India,[42] but none are supported by the genetic and molecular evidence.[40]
Until recently, theaye-aye has been difficult to place within Strepsirrhini.[1] 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.[40]
SuborderHaplorhini, the simple-nosed or "dry-nosed" primates, is composed of two sister clades.[1]Prosimian tarsiers in the family Tarsiidae (monotypic in its own infraorder Tarsiiformes), represent the mostbasal division, originating about 58 mya.[48][49] The earliest known haplorhine skeleton, that of 55 MA old tarsier-likeArchicebus, was found in central China,[50] supporting an already suspected Asian origin for the group.[51] The infraorderSimiiformes (simian primates, consisting of monkeys and apes) emerged about 40 mya,[43] possibly also in Asia; if so, theydispersed across theTethys Sea from Asia to Africa soon afterwards.[52] There are two simian clades, bothparvorders:Catarrhini, which developed in Africa, consisting ofOld World monkeys, humans and the other apes, and Platyrrhini, which developed in South America, consisting ofNew World monkeys.[1] A third clade, which included theeosimiids, developed in Asia, but became extinct millions of years ago.[53]
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.[35][54] The anthropoid primates possibly traversed the Atlantic Ocean from Africa to South America during theEocene byisland hopping, facilitated byAtlantic Ocean ridges and a lowered sea level.[42] Alternatively, a singlerafting event may explain this transoceanic colonization. Due tocontinental drift, the Atlantic Ocean was not nearly as wide at the time as it is today.[42] Research suggests that a small 1 kg (2.2 lb) primate could have survived 13 days on a raft of vegetation.[55] 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 theMiocene.[56] 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.[43] Old World monkeys disappeared from Europe about 1.8 mya.[57] Molecular and fossil studies generally show that modern humans originated in Africa 100,000–200,000 years ago.[58]
Although primates are well studied in comparison to other animal groups, several new species havebeen discovered recently, and genetic tests have revealed previously unrecognised species in known populations.Primate Taxonomy listed about 350 species of primates in 2001;[19] the author,Colin Groves, increased that number to 376 for his contribution to the third edition ofMammal Species of the World (MSW3).[1] However, publications since the taxonomy in MSW3 was compiled in 2003 have pushed the number to 522 species, or 708 including subspecies.[59]
Hybrids
Primatehybrids usually arise in captivity,[60] but there have also been examples in the wild.[61][62] Hybridization occurs where two species' range overlap to formhybrid zones; hybrids may be created by humans when animals are placed in zoos or due to environmental pressures such as predation.[61] 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 thegelada and thehamadryas baboon.[63]
Primate skulls showingpostorbital bar, and increasing brain sizes
The primate skull has a large, domedcranium, which is particularly prominent inanthropoids. The cranium protects the large brain, a distinguishing characteristic of this group.[69] The endocranial volume (the volume within the skull) is three times greater inhumans than in the greatest nonhuman primate, reflecting a larger brain size.[70] The mean endocranial volume is 1,201 cubic centimeters in humans, 469 cm3 ingorillas, 400 cm3 inchimpanzees and 397 cm3 inorangutans.[70] The primary evolutionary trend of primates has been the elaboration of the brain, in particular theneocortex (a part of thecerebral cortex), which is involved withsensory perception, generation ofmotor commands, spatial reasoning,conscious thought and, in humans,language.[71] While other mammals rely heavily on theirsense of smell, the arboreal life of primates has led to atactile,visually dominant sensory system,[71] a reduction in the olfactory region of the brain and increasingly complex social behavior.[72] The visual acuity ofhumans and otherhominids is exceptional; they have the mostacute vision known among all vertebrates, with the exception of certain species ofpredatory birds.[73][74]
Primates have forward-facing eyes on the front of the skull;binocular vision allows accurate distance perception, useful for thebrachiating ancestors of all great apes.[69] Abony ridge above the eye sockets reinforces weaker bones in the face, which are put under strain during chewing.Strepsirrhines have apostorbital bar, a bone around the eye socket, to protect their eyes; in contrast, the higher primates,haplorhines, have evolved fully enclosed sockets.[75]
An 1893 drawing of the hands and feet of various primates
Primates show an evolutionary trend towards a reducedsnout.[76] Technically, Old World monkeys are distinguished from New World monkeys by the structure of the nose, and from apes by thearrangement of their teeth.[72] In New World monkeys, the nostrils face sideways; in Old World monkeys, they face downwards.[72] Dental pattern in primates vary considerably; although some have lost most of theirincisors, all retain at least one lower incisor.[72] In most strepsirrhines, the lower incisors form atoothcomb, which is used in grooming and sometimes foraging.[72][77] Old World monkeys have eightpremolars, compared with 12 in New World monkeys. The Old World species are divided into apes and monkeys depending on the number ofcusps on theirmolars: monkeys have four, apes have five[72] - although humans may have four or five.[78] 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.
Body
Vervet hindfoot showing fingerprint ridges on the sole
Primates generally have five digits on each limb (pentadactyly), with a characteristic type of keratinfingernail on the end of each finger and toe. The bottom sides of the hands and feet havesensitive pads on thefingertips. Most haveopposable thumbs, a characteristic primate feature most developed inhumans, though not limited to this order (opossums andkoalas, for example, also have them).[69] Thumbs allow some species to usetools. In primates, the combination of opposing thumbs, short fingernails (rather than claws) and long, inward-closing fingers is arelict of the ancestral practice of gripping branches, and has, in part, allowed some species to developbrachiation (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, calledtoilet-claws, which they use for grooming.[69]
Distinct sexual size dimorphism can be seen between the male and female gorilla.
Sexual dimorphism is often exhibited insimians, 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 inbody mass[82][83] and canine tooth size[84][85] along withpelage and skin color.[86] The dimorphism can be attributed to and affected by different factors, includingmating system,[87] size,[87] habitat and diet.[88]
Comparative analyses have generated a more complete understanding of the relationship betweensexual selection,natural selection, and mating systems in primates. Studies have shown that dimorphism is the product of changes in both male and female traits.[89] Ontogenetic scaling, where relative extension of a common growth trajectory occurs, may give some insight into the relationship between sexual dimorphism and growth patterns.[90] Some evidence from the fossil record suggests that there wasconvergent evolution of dimorphism, and some extincthominids probably had greater dimorphism than any living primate.[89]
Locomotion
Diademed sifaka, a lemur that is a vertical clinger and leaper
Primate species move bybrachiation,bipedalism,leaping, arboreal and terrestrialquadrupedalism,climbing,knuckle-walking or by a combination of these methods. Several prosimians are primarily vertical clingers and leapers. These include manybushbabies, allindriids (i.e.,sifakas,avahis andindris),sportive lemurs, and alltarsiers.[91] Other prosimians are arboreal quadrupeds and climbers. Some are also terrestrial quadrupeds, while some are leapers. Most monkeys are both arboreal and terrestrial quadrupeds and climbers.Gibbons,muriquis andspider monkeys all brachiate extensively,[57] with gibbons sometimes doing so in remarkably acrobatic fashion.Woolly monkeys also brachiate at times.[92]Orangutans use a similar form of locomotion called quadramanous climbing, in which they use their arms and legs to carry their heavy bodies through the trees.[57]Chimpanzees andgorillas knuckle walk,[57] and can move bipedally for short distances. Although numerous species, such asaustralopithecines andearly hominids, have exhibited fully bipedal locomotion, humans are the only extant species with this trait.[93]
Theevolution of color vision in primates is unique among mosteutherian mammals. While the remotevertebrate ancestors of the primates possessedthree color vision (trichromaticism), thenocturnal,warm-blooded, mammalian ancestors lost one of three cones in theretina during theMesozoic era. Fish,reptiles and birds are therefore trichromatic ortetrachromatic, while all mammals, with the exception of some primates andmarsupials,[94] are dichromats ormonochromats (totally color blind).[77] Nocturnal primates, such as thenight monkeys andbush babies, are often monochromatic. Catarrhines are routinely trichromatic due to agene duplication of the red-greenopsin gene at the base of their lineage, 30 to 40 million years ago.[77][95] Platyrrhines, on the other hand, are trichromatic in a few cases only.[96] Specifically, individual females must beheterozygous for twoalleles of the opsin gene (red and green) located on the samelocus of theX chromosome.[77] Males, therefore, can only be dichromatic, while females can be either dichromatic or trichromatic. Color vision in strepsirrhines is not as well understood; however, research indicates a range of color vision similar to that found in platyrrhines.[77]
Like catarrhines, howler monkeys (a family of platyrrhines) show routine trichromatism that has been traced to an evolutionarily recentgene duplication.[97] Howler monkeys are one of the most specialized leaf-eaters of the New World monkeys; fruits are not a major part of their diets,[92] 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.[96]
Behavior
Social systems
Richard Wrangham stated thatsocial systems of primates are best classified by the amount of movement by females occurring between groups.[98] 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.[98] This organization can be seen inchimpanzees, where the males, who are typically related, will cooperate in defense of the group's territory.[99] Evidence of this social system has also been found amongNeanderthal remains inSpain[100] and in remains ofAustralopithecus andParanthropus robustus groups in southern Africa.[101][102] Among New World Monkeys,spider monkeys andmuriquis use this system.[103]
A social huddle ofring-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.[98]Indri,lariang tarsiers,Callitrichidae monkeys and gibbons use this system, although "monogamy" in this context does not necessarily mean absolute sexual fidelity.[104][105] These species do not live in larger groups.
Solitary species – males and females live in overlapping home ranges.[98][105] This type of organization is found in lorises, galagos,mouse lemurs, aye-ayes and orangutans.[105]
Other systems are known to occur as well. For example, withhowler monkeys andgorillas 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.[92][106] Some prosimians,colobine monkeys andcallitrichid monkeys also use this system.[57]
The transfer of females or males from their native group is likely an adaptation for avoiding inbreeding.[107] 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.[107][108] This effect of inbreeding on infant mortality is probably largely a result of increased expression of deleterious recessive alleles (seeInbreeding depression).
PrimatologistJane Goodall, who studied in theGombe Stream National Park, notedfission-fusion societies in chimpanzees.[109] There isfission when the main group splits up to forage during the day, thenfusion when the group returns at night to sleep as a group. This social structure can also be observed in thehamadryas baboon,[110]spider monkeys[92] and thebonobo.[110] Thegelada has a similar social structure in which many smaller groups come together to form temporary herds of up to 600 monkeys.[110]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.[111]
These social systems are affected by three main ecological factors: distribution of resources,group size, andpredation.[112] Within a social group there is a balance between cooperation and competition. Cooperative behaviors in many primates species includesocial grooming (removingskin 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 establishingdominance hierarchies.[112][113]
In November 2023, scientists reported, for the first time, evidence that groups of primates, particularlybonobos, are capable of cooperating with each other.[114][115]
In South America,squirrel monkeys associate withcapuchin monkeys.[119] This may have more to do with foraging benefits to the squirrel monkeys than anti-predation benefits.[119]
Themating systems of primates vary betweenmonogamy,polyandry,polygyny andpolygynandry. In monogamous species, adult males and females form long-lastingpair bonds. Compared to other systems, there is little competition for mating rights and males and females tend to be similar in size. Polyandry, which involves groups consisting of single females mating with multiple males, may arise as a secondary mating system in monogamous species. In thebrown-mantled tamarin, a female may breeding with one or two males. Polyandry may have developed due to the high frequency of twin births, which require more help in raising.[105]
Polygynous species include gorillas,Hanuman langurs, geladas, hamadryas baboons,proboscis monkeys, andgolden snub-nosed monkeys, and consists of one male mating with multiple females within aharem or one-male unit. Sexual dimorphism tends to be higher in these species and males may also develop prominentsecondary sex characteristics. In the patriarchal hamadryas baboon, the males aggressively herd females into their groups and violently discipline those that wander. By contrast, in gelada society, which is based on female kinship, a male is dependent on the support of the females in his unit and cannot impose on them. Polygynous males must defend their harems from rivals, who may try to take over.[105]
In some species, such as ring-tailed lemurs,sifakas,macaques, mostbaboons,mangabeys,squirrel monkeys,woolly monkeys, spider monkeys,woolly spider monkeys, chimpanzees and bonobos, both males and females mate with multiple partners. Polygynandry occurs inmultimale-multifemale groups, and since females mate many times before conception, males have large testicles forsperm competition. Males may exist in adominance hierarchy and those at the top will try to monopolize access to the females. Consortships may occur in some species but these are short-term. In solitary-living species, males and females mate with partners whose home ranges they overlap with. This is known as a 'dispersed' mating system.[105]
Genetic evidence indicates that humans were predominantlypolygynous for most of their existence as a species, but that this began to shift during the Neolithic, whenmonogamy started becoming widespread concomitantly with the transition from nomadic to sedentary societies.[120] Most modern human societies consist of monogamousmarriages, but allow for polygyny, particularly for those of a high status.[105]
Female primates may signal to the male their receptiveness though various displays including eye-contact, tongue-clicking and presenting of the rump. Female lemurs, lorises and galagos will position themselves in thelordosis pose while female chimpanzees, bonobos and some Old World monkeys developsexual swellings on the rump. Copulation in primates typically involves the males mounting the females from behind, as with most mammals. Belly-to-belly copulation has been recorded in apes, both gibbons and the great apes. Humansex positions are modifications of these two positions.[121]
Primates may egage in sexual activity as part of social bonding; includinghomosexual behaviour.[121] Such behavior play an important role in bonobo society in particular. female bonobos engage in mutual genital-rubbing behavior, possibly to bond socially with each other, thus forming a female nucleus of bonobo society. The bonding among females enables them to dominate most of the males.[122]
Primates have slower rates of development than other mammals. All primate infants arebreastfed 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 ceaseovulation while breastfeeding an infant; once the infant isweaned the mother can reproduce again. This often leads to weaning conflict with infants who attempt to continue breastfeeding.[57]
Infanticide is common in polygynous species such asgray 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.[123] Polygynandry may also lessen the risk of infanticide since paternity becomes uncertain.[124]
Primates have a longerjuvenile period between weaning and sexual maturity than other mammals of similar size.[57] Some primates such asgalagos andNew World monkeys use tree-holes fornesting, 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.[125][126] During the juvenile period, primates are more susceptible than adults topredation andstarvation; they gain experience in feeding and avoiding predators during this time.[57] They learn social and fighting skills, often through playing.[57] Primates, especially females, have longer lifespans than other similarly sized mammals,[57] this may be partially due to their slower metabolisms.[127] Late in life, female catarrhine primates appear to undergo a cessation of reproductive function known asmenopause; other groups are less studied.[128]
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.[129] Most primates include fruit in their diets to obtain easily digested nutrients includingcarbohydrates andlipids for energy.[57] Primates in the suborderStrepsirrhini (non-tarsier prosimians) are able to synthesizevitamin C, like most other mammals, while primates of the suborderHaplorhini (tarsiers, monkeys and apes) have lost this ability, and require the vitamin in their diet.[130]
Many primates have anatomical specializations that enable them to exploit particular foods, such as fruit, leaves, gum orinsects.[57] For example, leaf eaters such as howler monkeys,black-and-white colobuses andsportive lemurs have extended digestive tracts which enable them to absorb nutrients from leaves that can be difficult to digest.[57]Marmosets, which are gum eaters, have strongincisor 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.[57] Theaye-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.[131] Some species have additional specializations. For example, thegrey-cheeked mangabey has thickenamel on its teeth, enabling it to open hard fruits and seeds that other monkeys cannot.[57] Thegelada is the only primate species that feeds primarily on grass.[132]
Hunting
Humans have traditionally hunted prey for subsistence.
Tarsiers are the onlyextantobligate carnivorous primates, exclusively eating insects, crustaceans, small vertebrates and snakes (includingvenomous species).[133]Capuchin monkeys can exploit many different types of plant matter, including fruit, leaves, flowers, buds, nectar and seeds, but also eat insects and otherinvertebrates, bird eggs, and small vertebrates such as birds,lizards,squirrels andbats.[92]
Thecommon chimpanzee eats anomnivorousfrugivorous diet. It prefers fruit above all other food items and even seeks out and eats them when they are not abundant. It also eats leaves and leaf buds, seeds, blossoms, stems, pith, bark and resin. Insects and meat make up a small proportion of their diet, estimated as 2%.[134][135] The meat consumption includes predation on other primate species, such as thewestern red colobus monkey.[117] Thebonobo is anomnivorousfrugivore – the majority of its diet is fruit, but it supplements this with leaves, meat from smallvertebrates, such asanomalures,flying squirrels andduikers,[136] andinvertebrates.[137] In some instances, bonobos have been shown to consume lower-order primates.[138][139]
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) withwild game, which must be hunted and killed in order to be consumed.[140] It has been proposed that humans have used fire to prepare andcook food since the time ofHomo erectus.[141] Around ten thousand years ago,humans developed agriculture,[142] which substantially altered their diet. This change in diet may also have altered human biology; with the spread ofdairy farming providing a new and rich source of food, leading to the evolution of the ability to digestlactose in some adults.[143][144]
As prey
Predators of primates include various species ofcarnivorans,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 differentantipredator adaptations includingcrypsis,alarm calls andmobbing. 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.[145]
Lemurs,lorises,tarsiers, and New World monkeys rely onolfactory signals for many aspects of social and reproductive behavior.[71] Specialized glands are used tomark territories withpheromones, which are detected by thevomeronasal organ; this process forms a large part of the communication behavior of these primates.[71] In Old World monkeys and apes this ability is mostlyvestigial, having regressed astrichromatic eyes evolved to become the main sensory organ.[146] Primates also use vocalizations, gestures, and facial expressions to convey psychological state.[147][148] 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.[149] Hand and arm gestures are also important forms of communication for great apes and a single gesture can have multiple functions.[148] Chest-beating in male gorillas is a form of visual and non-vocal sound communication that serves to show fitness to both rivals and females.[150]
Primates are a particularly vocal group of mammals.[81]Indris andblack-and-white ruffed lemurs make distinctive, loud songs and choruses which maintain territories and act asalarm calls.[151] ThePhilippine tarsier, has a high-frequency limit of auditory sensitivity of approximately 91 kHz with a dominant frequency of 70 kHz, among the highest recorded for any terrestrial mammal. For Philippine tarsiers, these 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.[152] Malehowler monkeys are among the loudest land mammals as their roars can be heard up to 4.8 km (3.0 mi), and relate to intergroup spacing, territorial protection and possibly mate-guarding.[153][154] Male and femalesiamangs both possess inflatable pouches in the throat with which pair -bonds use to sing "duets" to each other.[155] Thevervet 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.[156] Furthermore, many primate species includingchimpanzees,[157]Campbell's mona monkeys[158] orDiana monkeys[159] have been shown to combine vocalizations in sequences, suggestingsyntax may not be uniquely humans as previously thought but rather evolutionary ancient, and its origins may be deeply rooted in the primate lineage.[160]
Consonant- and vowel-like sounds exist in some orangutan calls and they maintain their meaning over great distances.[161] The time range for the evolution of human language and/or its anatomical prerequisites extends, at least in principle, from the phylogenetic divergence ofHomo (2.3 to 2.4 million years ago) fromPan (5 to 6 million years ago) to the emergence of fullbehavioral modernity some 50,000–150,000 years ago. Few dispute thatAustralopithecus probably lacked vocal communication significantly more sophisticated than that ofgreat apes in general.[162]
Primates have advanced cognitive abilities: some make tools and use them to acquire food and for social displays;[163][164] some can perform tasks requiring cooperation, influence and rank;[165] they are status conscious, manipulative and capable of deception;[166][167] they can recognisekin andconspecifics;[168][169] and they can learn to use symbols and understand aspects of human language including some relational syntax and concepts of number and numerical sequence.[170][171][172] Research in primate cognition explores problem solving, memory, social interaction, atheory of mind, and numerical, spatial, and abstract concepts.[173] 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.[174][175] However, there is a great deal of variation in each group (e.g., among New World monkeys, bothspider[174] andcapuchin monkeys[175] have scored highly by some measures), as well as in the results of different studies.[174][175]
In 1960,Jane Goodall observed achimpanzee poking pieces of grass into atermite 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.[176] There are more limited reports of the closely relatedbonobo 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.[177] It has been reported that females, both chimpanzee and bonobo, use tools more avidly than males.[178]Orangutans inBorneo scoop catfish out of small ponds. Over two years, anthropologist Anne Russon observed orangutans learning to jab sticks at catfish to scare them out of the ponds and in to their waiting hands.[179] There are few reports ofgorillas using tools in the wild. An adult femalewestern 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.[180]
The first direct observation of a non-ape primate using a tool in a wild environment occurred in 1988. Primatologist Sue Boinski watched an adult male white-faced capuchin beat afer-de-lance snake to death with a dead branch.[181] The black-striped capuchin was the first non-ape primate for which routine tool use was documented in the wild; individuals were observedcracking nuts by placing them on a stone anvil and hitting them with another large stone.[182] In Thailand and Myanmar,crab-eating macaques use stone tools to open nuts, oysters and other bivalves, and various types of sea snails.[183] 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.[184]
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.[185]
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.[176] Chimpanzees have also been observed making "sponges" out of leaves and moss that suck up water.[186] 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.[187][188] In the wild, mandrills have been observed to clean their ears with modified tools. Scientists filmed a large male mandrill atChester Zoo (UK) stripping down a twig, apparently to make it narrower, and then using the modified stick to scrape dirt from underneath its toenails.[189] Captive gorillas have made a variety of tools.[190]
Humans are the mostadaptable primate species, despite having a low or narrow tolerance for many of the earth's extreme environments.[191] Currently the species is present in all eightbiogeographical realms, although their presence in theAntarctic realm is very limited toresearch stations and annually there is a population decline in the winter months of this realm.
Non-human primates primarily live in thetropical latitudes of Africa, Asia, and the Americas. Species that live outside of the tropics include theJapanese macaque which lives in the Japanese islands ofHonshū andHokkaido; theBarbary macaque which lives in North Africa and several species of langur which live in China. Primates tend to live intropical rainforests but are also found intemperate forests,savannas,deserts, mountains and coastal areas.[192] The number of primate species within tropical areas has been shown to be positivelycorrelated to the amount of rainfall and the amount of rain forest area.[193] Accounting for 25% to 40% of thefruit-eating animals (byweight) within tropical rainforests, primates play an importantecological role by dispersing seeds of many tree species.[194]
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.[205] The expanding Chinese middle class has increased demand for NHPs as exotic pets in recent years.[206] Although NHP import for the pet trade was banned in the U.S. in 1975, smuggling still occurs along theUnited States – Mexico border, with prices ranging fromUS$3000 for monkeys to $30,000 for apes.[207]
NHPs are kept inzoos 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.[210]
Thousands of non-human primates are used around the world in research because of their psychological and physiological similarity to humans.[211][212] In particular, the brains and eyes of NHPs more closely parallel human anatomy than those of any other animals. NHPs are commonly used inpreclinical trials,neuroscience,ophthalmology studies, and toxicity studies.Rhesus macaques are often used, as are othermacaques, Africangreen monkeys, chimpanzees,baboons,squirrel monkeys, andmarmosets, both wild-caught and purpose-bred.[211][213]
In 2005, GAP reported that 1,280 of the 3,100 NHPs living in captivity in the United States were used for experiments.[202] In 2004, theEuropean Union used around 10,000 NHPs in such experiments; in 2005 in Great Britain, 4,652 experiments were conducted on 3,115 NHPs.[214] 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.[215] European groups such as theEuropean 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.[216]
Extinction threats
Humans are known to hunt other primates for food, calledbushmeat. Pictured are two men who have killed a number ofsilky sifaka andwhite-headed brown lemurs.
TheInternational 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.[217] Additionally, 75% of primate species have decreasing populations.[217] Trade is regulated, as all species are listed byCITES inAppendix II, except 50 species and subspecies listed inAppendix I, which gain full protection from trade.[218][219]
Common threats to primate species includedeforestation,forest fragmentation,monkey drives (resulting from primate crop raiding),[220] 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.[221][222][223] More than 90% of primate species occur in tropical forests.[222][224] 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.[224] In Indonesia large areas of lowland forest have been cleared to increasepalm oil production, and one analysis of satellite imagery concluded that during 1998 and 1999 there was a loss of 1,000Sumatran orangutans per year in theLeuser Ecosystem alone.[225]
Primates with a large body size (over 5 kg) are at increased extinction risk due to their greater profitability topoachers compared to smaller primates.[224] 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.[226] Data for some African cities show that half of all protein consumed in urban areas comes from thebushmeat trade.[227] Endangered primates such asguenons and thedrill are hunted at levels that far exceed sustainable levels.[227] This is due to their large body size, ease of transport and profitability per animal.[227] As farming encroaches on forest habitats, primates feed on the crops, causing the farmers large economic losses.[228] Primate crop raiding gives locals a negative impression of primates, hindering conservation efforts.[229]
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.[71] Among the primates wiped out wereArchaeoindris (a lemur larger than a silverback gorilla) and the familiesPalaeopropithecidae andArchaeolemuridae.[71]
In Asia,Hinduism,Buddhism, andIslam prohibit eating primate meat; however, primates are still hunted for food.[224] Some smaller traditional religions allow the consumption of primate meat.[230][231] The pet trade and traditional medicine also increase demand for illegal hunting.[206][232][233] Therhesus macaque, amodel 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.[223]
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.[221][234] This increases the amount of forest vulnerable toedge effects such as farmland encroachment, lower levels of humidity and a change in plant life.[235][236] Movement restriction results in a greater amount of inbreeding, which can cause deleterious effects leading to apopulation bottleneck, whereby a significant percentage of the population is lost.[237][238]
^Although themonophyletic 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 theclade of toothcombed primates into oneinfraorder and the extinct, non-toothcombedadapiforms into another, both within thesuborder Strepsirrhini.[20][21] However, another popular alternative taxonomy places thelorisoids in their own infraorder, Lorisiformes.[22]
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