The first social interactions of a newborn primate are with mother. The mountain gorilla is very careful to support her young infant as it clings to her. All primates seek contact with mother as soon as they are born -- and most are able to cling on their own within a day or two of birth.

Unlike many other animals, primates do not leave their infants in a nest or other protected area. Instead, mothers carry their infants wherever they go. Infants may cling to the belly or, as this young uakari is doing, ride on mother's back. Scientific name: Cacajao calvus uakari -- wah-CAR-ee

When they are at rest, mother and baby usually sleep in ventral-ventral, or belly-to-belly, contact. But a curious infant, such as this spider monkey, spends as much time as possible looking around at the world. Scientific name: Ateles geoffroyi

Meeting the other members of the social group is an important experience for young primates. Here a juvenile spider monkey is contacted by the new infant. Juvenile spider monkey looks at infant on mother's back. Juvenile refers to the years between infancy and adulthood. For spider monkeys this is years old.

For primates, as all other mammals, mother is a source of food. This young Japanese macaque nurses while its mother is groomed by another monkey. At first, mothers carefully guard their infants, and may prevent others from touching the new baby. Interested animals are allowed near the infant only after reassuring the mother of their friendly intentions. Mother Japanese macaque holds nursing infant while troop member grooms her. Scientific name: Macaca fuscata macaque -- ma-KACK

Contact with the mother is an important first social experience for humans, too.

Although all primates live in social groups, the nature of those groups differs between species. Group size, the number of adult males and adult females, and who does most of the breeding all vary between species.

The siamangs shown here live in a family unit consisting of an adult male, adult female and their young offspring. This is similar to the basic living unit of many humans -- mom, dad and the kids. Family group of siamangs showing adult male (top), adult female (middle) and their offspring (bottom). Scientific name: Symphalangus syndactylus siamangs -- SI-a-mangs

Other primates live in groups with only one adult male and several adult females plus their offspring. In a gorilla group the adult male, called a silverback, fathers the offspring of all the females living with him. Group of mountain gorillas in African forest.

The single male group structure is also found in some species of monkey. Here the large male hamadryas baboon walks at the front of a group of adult females. A group of female hamadryas baboons follow the large adult male in a zoo enclosure. hamadryas -- hom-uh-DRY-us Notice the genital swellings on one female. These indicate sexual receptivity.

Multi-male groups are also common among the primates. Chimpanzee bands are made up of several adults of both sexes and their offspring. Such bands are temporary associations of animals who live in a larger community. Relationships between adult males are very important in these groups. Three male chimpanzees sit together. Photo taken in a zoo group. Scientific name: Pan troglodytes

Some species of monkeys, such as these stumptail macaques, also live in groups with more than one adult of each sex. Relationships among adult females are most important in the social structure of these stable troops A group of stumptail macaques feeding. Scientific name: Macaca arctoides macaques -- ma-KACKS

All primates need to learn how to be a successful member of a social group. Young animals spend a great deal of time learning social skills through play. This young chimpanzee invites a companion to play.

All primates play. Here a group of lemurs engage in the most common form of play. This activity, characterized by chasing and wrestling, is called rough-and-tumble play. It seems to allow young animals to learn their own strengths and weaknesses, as well as that of their peers. Group of ring-tailed lemurs wrestling. Scientific name: Lemur catta lemurs -- LEE-mers

Social play occurs when two or more individuals engage in a behavior that has no apparent serious purpose, although it may resemble the behaviors used by adults in their social lives. Humans often call this playing games.

For most primates, play involves physical contact. Here are two chimpanzees wrestling.

Gorillas like to wrestle too

Play frequently occurs between animals of different sizes. These gorillas are engaging in rough play, but the smaller animal rarely gets hurt in a play bout. A young lowland gorilla plays with an older juvenile in a zoo. Scientific name: Gorilla gorilla gorilla

Even in the roughest form of play, animals are seldom hurt. Older animals know that if a younger animal is hurt or scared, a scream can bring mother running to defend her baby. This interaction between a juvenile chimpanzee and an infant may look dangerous, but both animals know it is only play. In the foreground, a juvenile chimpanzee drags an infant. Adult female chimpanzees in background appear unconcerned, while another infant watches the play bout.

Knowing the intentions of other group members is vitally important to social animals. Primates use all the senses -- sight, smell, hearing, taste and touch -- in communicating with each other.

All primates rely heavily on vision to explore their world. It is not surprising that facial expressions are an important communication tool. The youngest animals quickly learn to recognize the play face. The rhesus macaques, shown here with mouth open, demonstrate the play face seen in all monkeys, apes, and even humans at play. Two rhesus monkeys wrestle.The animal on top (with head upside down) shows the open mouth play face. Scientific name: Macaca mulatta rhesus macaques - REE-sus ma-KACKS

Friendly intentions are also being communicated here by the rhesus monkey looking towards the camera. She is lip-smacking, an active facial expression that invites another animal to join the group. A group of rhesus monkeys. One animal looks toward the camera. Photo taken in a zoo enclosure. To lip-smack, pucker up your lips, and open and close t hem rapidly.

Primates are also very good at communicating when they are not happy about a social interaction. Here another rhesus monkey screams and grins. This bared teeth expression is usually shown by the loser in a less-than-friendly encounter. A mother rhesus macaque at center with her offspring responds to threats from two other monkeys.

Many primate species have unusual faces. This golden snub-nosed monkey from China shows an eye-catching combination of contrasting facial colors. Closeup of face of a golden snub-nosed monkey. The flaps of skin at the corners of the mouth are a normal facial feature of adult males in this species.

Scientists think one purpose of such a face is that it permits other animals to get a very clear view of all facial expressions. The yawn has several meanings for primates. A yawning animal is more likely to be nervous than tired. A golden snub nosed monkey yawns, showing large canine teeth. Scientific name: Rhinopithecus roxellanae Most adult male higher primates have large canine teeth. Humans are an exception

Primates pay close attention to the body language of other members of their group. Here a chimpanzee begins an action that is also performed by humans. An adult chimpanzee with back to camera begins to bow to a second chimpanzee.

The bow is a sign of submission that indicates to the animal receiving it that he or she is dominant. Most primate groups have a dominance hierarchy. Lower ranking animals can avoid fights with higher ranking animals by performing a formal sign of submission, such as a bow, when tensions are high.

Primate body language can be very impressive. Here an adult male chimpanzee, on the left, stands with all his hair on end. This is called piloerection -- it makes an animal look larger to the nearby audience. Three chimpanzees in a zoo enclosure. The adult male on the left facing the camera is getting ready to run by the animals on the right.

Next, the chimpanzee male charges past the group members he is trying to impress. Adult male chimpanzee runs past two other chimpanzees. Edge of enclosure is marked by moat in the foreground.

Chimpanzees may also charge directly at another individual. This kind of display does not signal the beginning of a fight -- only an attempt to impress another animal. In this picture, two males are confronting each other. Two adult male chimpanzees confront each other. Animal in the foreground stands bipedally and is piloerected.

In a tense situation, animals usually can tell when a conflict is about to occur. Here one chimpanzee chases a displaying opponent away. Three chimpanzees on climbing structure in zoo enclosure. Piloerected animal in front had been displaying. Male in center is chasing him away.

Body posture also signals when an opponent no longer wants to fight. This screaming chimpanzee's lowered body position indicates submission. Screaming chimpanzee crouches on the ground.

These lemurs are using another kind of body language - - signaling with their tails in the air. Tail position can communicate alertness and self-confidence. Three ring-tailed lemurs from a captive group stand with tails in 'question mark' position. Animals are wearing identification collars.

Body language is also important in humans. A hand- shake is a common expression of goodwill between people.

Primates use their sense of smell to communicate, too. Here a sifaka leaves a scent mark on a tree. A sifaka (related to the lemurs) rubs a scent-producing anal gland against the bark of a tree. Scientific name: Propithecus verreauxi sifaka -- sih-FAHK-ah

A cotton-top tamarin sniffs at a scent left by another individual in a captive group of monkeys. Scents may mark territorial boundaries, let other animals know where to find food, or communicate when animals of the opposite sex are ready to mate. A cotton-top tamarin, a small South American monkey, sniffs at an odor- containing vial. This animal lives in a captive group used in studies of communication. Scientific name: Saguinus oedipus tamarin -- TAM-ah-rin

Primates use sound to communicate as well. Many animals have complex calls that let others know of danger, or when they are intruding on another group's territory. This howler monkey gets its name from the loud call it produces. A brown howler -- a South American monkey -- faces right as it calls from a tree. Notice the enlarged lower jaw which allows this monkey to produce a loud, resonating call. Scientific name: Alouatta fusca

Most primates live in forests, and are able to produce some calls that carry long distances, such as hooting by this chimpanzee. Softer sounds are used when group members are near each other. Humans use sound to communicate when they talk. Hear a chimp laugh Adult male chimpanzee stands bipedally and hoots.

Gorillas More Primate Sounds Bonobo Orangutan

Touch is a very important sense for primates. Social animals have many friendly interactions throughout the day -- and most involve some form of touch. Mothers and infants spend a lot of time in contact, as do play partners, sexual partners, and other members of a social group.

These young macaques are using in a play bout a form of touch used by adults to initiate a sexual interaction. The animal standing on four feet is presenting her rear end to a partner. He responds by touching her hips and standing. Two young macaques from a mixed species captive group. The female stands quadrupedally while the male stands behind her.

An adult female stumptail macaque presents to an adult male. He responds by touching her rear, and visually inspecting it for signs that she is in her fertile period and thus ready to mate. An adult female stumptail macaque presents her genital area to an adult male. He will look, smell, touch and even taste her secretions to learn if she is ready to mate. Primates rely on many signals to determine the reproductive state of animals of the opposite sex.

Here a female chimpanzee presents to a male. The swollen skin around her genitals gives a visual signal that she is fertile. A female chimpanzee (lying on her side) presents her genitals to an adult male.

A typical copulation or mating in most primates involves the male mounting the female from the rear A male Japanese macaque mounts a female.

The female Japanese macaque reaches back and looks at her partner during their mating. Later in the same sequence, the female Japanese macaque looks over her shoulder at the male. This often occurs when the male ejaculates.

Physical contact between animals is a part of most friendly interactions in primates. Here two Japanese macaques sit together in close contact

These golden snub- nosed monkeys show the same pattern of contact. This type of touch, called a huddle, can occur when animals are resting or sleeping. Two golden snub-nosed monkeys, living in a Chinese research facility, embrace. Monkeys do huddle in cold weather for warmth. In the wild snub- nosed monkeys survive snowy winters. However all monkeys huddle, even in the hottest weather, for social contact

Another very important friendly physical contact is social grooming. Here one monkey grooms a partner who is offering her chest to be groomed. A female Japanese macaque lies on her back while another animal grooms her.

When animals groom, they look through the fur and remove any debris they find, such as dirt, dead skin or parasites. An adult female hamadryas baboon (an African monkey) grooms an adult male.

Social grooming not only helps animals keep clean; it reinforces bonds between related animals and other members of a social group. Three long-tailed macaques sit together. The adult female in the center grooms a juvenile on the right. Scientific name: Macaca fascicularis

In a group of monkeys, such as these long-tailed macaques, mothers groom their infants; females groom males; males groom females; older offspring groom their mother. All combinations of grooming partners are possible. A large group of long-tailed macaques, including some mothers holding infants on their bellies, sit together. An adult male in the top row is being groomed by two other animals.

In a group of monkeys, such as these long-tailed macaques, mothers groom their infants; females groom males; males groom females; older offspring groom their mother. All combinations of grooming partners are possible. A large group of long-tailed macaques, including some mothers holding infants on their bellies, sit together. An adult male in the top row is being groomed by two other animals.

Social animals don't always get along with the members of their group. Fights and other forms of aggression are a common occurrence in primate groups.

Unfriendly behavior usually begins with a threat. Here an adult gorilla shows the body posture and facial expression that lets an opponent know a fight is possible. Adult female lowland gorilla (standing), living in a zoo group, stares at an opponent off-camera. A juvenile sits near her. This is called a pursed lip threat posture. Look at the stiff arms and the tight position of the lips.

Staring at an opponent is often part of a threat. This rhesus macaque shows the open mouth threat face used by many species of monkey. A female rhesus macaque holding an infant stares off camera at an opponent.

Other parts of the body can be shown as part of a threat. Here a marmoset flashes the colors on her rear end; other group members know this a threat. A pygmy marmoset, a South American monkey, viewed from the rear.

Not all threats lead to fights. Most of the time the opponent will leave or show submission. Sometimes threats are just ignored. But fights do occur. Here an adult male chimpanzee attacks a female carrying an infant A fight between chimpanzees living in a zoo group. A female holding an infant, in the foreground, is attacked by an adult male behind her. She is screaming in submission.

Fights can have serious consequences. A long-tailed macaque shows injuries received in a fight. Animals can be badly hurt or even die as the result of fighting. A long-tailed macaque, on the right, shows wounds on the shoulder. This type of slash wound can be inflicted by adult males with their large canine teeth. In most primate species, animals are not killed or even seriously injured during fighting but a few may die later due to shock or infection.

Early observers of gorillas were impressed with their threats and displays. Here an adult male stands on two legs and beats his chest. This gained the gorilla the reputation as a very aggressive animal. Actually they are among the most peaceful of the primates. Adult male silverback mountain gorilla stands bipedally while displaying in an African forest. Gorillas use a cupped hand position to make the sound associated with chest beating.

The chimpanzee can be very aggressive. However, as with all primates, most aggression does not lead to serious consequences. Here a male shakes a branch as part of a display. If his opponent does not back down, a fight may occur. A piloerected adult male chimpanzee shakes a branch while another animal watches. While many conflicts between chimpanzees involve only noisy displays, chimpanzees are the one primate besides humans known to kill adult animals of the same species during a fight.

Often fights are followed by reconciliation or making up by the opponents. Animals who continue to live in the same group may make an effort to repair the social relationship interrupted by their fight. This usually involves some form of friendly touch, such as grooming, or even just sitting next to each other while eating. Two mountain gorillas feed next to each other in the forest.

Fights between groups also occur. Here members of two troops of green monkeys face off. Again, threats and displays are the most likely form of aggression. Members of two groups of African green monkeys threaten each other. Scientific name: Cercopithecus aethiops

All the members of a group may get involved in an intertroop fight. These rhesus macaques threaten each other. In this species, females are often at the front when aggressive encounters with other groups occur Two large troops of rhesus monkeys threaten each other. Notice that several females carrying infants are in the front ranks.

A fight between groups may involve members of both sexes. Males and females are at the front in this conflict between neighboring hamadryas baboon troops. Hamadryas baboon groups come to blows at an African water hole. Adult males have long fur on their face and shoulders.

Sometimes intergroup fights involve males only.

Knowing all the members of its group is important to a social animal. New animals may migrate into a group from other areas -- but most new members of a group are born there.

Everyone is interested in new babies. This adult male gorilla gently touches an infant. Adult male lowland gorilla touches a young infant in a zoo enclosure.

In most species, mothers do most of the child care. However in some species, fathers may carry infants most of the time. Here a tamarin male carries a youngster. Adult male saddleback tamarin carries a youngster on his back. Scientific name: Saguinus fuscicollis

Juveniles also spend a lot of time with infants. These young gorillas take turns carrying the newest member of their social group. A rare photo. Twin male gorillas born in a zoo carry a younger animal who had been adopted by an adult female in their group.

An adult female chimpanzee plays with a young animal. The two animals are not related. This kind of behavior, a friendly interaction between an adult female and an unrelated youngster, is called aunting behavior An adult female chimpanzee wrestles with an unrelated youngster. This is also called alloparenting. It occurs whenever someone other than the mother carries or defends a young animal. Juveniles, especially females, are most likely to do this, but other group members may also show protective behavior towards infants.

Grandparents may also have a special interest in the next generation. All primates must have the ability to adapt to changing social relationships. They begin learning social skills at birth and continue to practice them throughout life.