Primate Behavior


We study nonhuman primate behavior to help us better understand our own species behavior.

Since we are primates - primate behavior includes humans. Yet, clearly there are differences in behavior among different species of primates - especially humans.

Similar behaviors may also have different causes. What may be instinctual in one species may be learned in another.

And yet the similarities may give us some knowledge of the roots of some human behaviors. All mammals can learn and rely at least partially on learned behavior for survival. Primates more than any other group of mammals and humans more than any other primate.

Five different areas of primate behavior:
I. Sexuality
II. Infant care and other care-giving
III. Grooming & touch
IV. Aggression & violence
V. Communication

It is important to understand the interactive relationship between these behaviors and the environment especially:

Food type and availability - all animals must have food and have adapted to use different resources.
Social structure - primates are social - especially humans. The social nature of primates is one of their primary adaptations to the environment, providing many benefits and many challenges.

Some benefits include the sharing of food resources, access to potential mates and the protection from predators.

But the challenges are intergroup competition for food resources and mates, as well as potential violence within the group.

Much of primate behavior rests in the balance of the individual need for access to resources with the need for the social group. Most anthropologists believe that the adaptation of the social group and the increased complexity this requires may be a primary factor in the larger, more complex brain of humans.

I. Sexuality - both for mating and for social relationships is an important part of primate behavior and quite variable from species to species. A few primates are monogamous. That means mating in an exclusive pair-bond until one of the pair dies. The species that are monogamous are usually arboreal, have minimal sexual dimorphism, and are territorial.

Many other primates like baboons, chimpanzees, and bonobos are not monogamous, mating with more than one other adult, not only over a life-time but often in one mating cycle. May form consortships and/or friendships. Consortships are temporary pairings that make last days or months.


One important controversy is the debate about the lack of estrus in human females.

Estrus is a period of sexual receptivity in female mammals correlated with ovulation. In chimpanzees for example, along with some other species, the genital areas of the female swell and turn bright red announcing her receptivity and fertility.

Humans have what is often referred to as concealed ovulation, meaning that not only is it not visible, but that the woman herself is not usually aware of exactly when she ovulates. And humans will engage in sexual behavior at any point in the female's cycle, even when she is already pregnant. This means that sex among humans is frequently (maybe even most of the time) non-procreative.

One theory put forward to explain why females "lost estrus" is that with concealed ovulation and continual sexual receptivity, females would be able to entice a male into a long-term pair bond where he would provide protection and food for her and her young in exchange for continual and exclusive sexual access to her.

This theory, usually put forward by some male anthropologists, has been challenged quite strongly - particularly by female anthropologists.

Physical anthropologist, Adrienne Zihlman called this the "ever-read vaginia theory" and said that this theory "had to be the product of either a very old man with a bad memory or a young man who would be very disappointed."

Problems -

  1. Although human males do show more interest in long term care of both infants and females, monogamy is not the norm in human sexual behavior.
  2. Women in both hunter/gatherer groups and agricultural groups traditionally provide up to 80% of the food for the group. Seems to be based on the "nuclear family of the US 1950s."
  3. Bonobos also practice sexual activity continuously and out of estrus, and yet they still have estrus cycles and are not monogamous.

Monogamy - to mate exclusive with one opposite sex mate (usually until mate dies).

Characteristics of Monogamous Mammals


  1. Territory - defended and exclusive
  2. Sexual activity - infrequent
  3. Same-sex adults - intolerant
  4. Offspring - leave parental group
  5. Social network - absent


  1. Territory - Access through symbols, shared
  2. Sexual activity - extremely variable
  3. Same-sex adults - form groups including initiation rituals and task-oriented groups
  4. Offspring - variable residence patterns, partilocal, matrilocal, usually maintain contact with parents
  5. Social network - elaborate, kin and non-kin social networks.

Most human groups do not practice monogamy. Most human sexual behavior includes more than one sexual partner for at least one sex. Many human cultures either sanction or tolerate sexual activity with more than one sexual partner. Even in cultures where monogamy or serial monogamy is the ideal, it may not be practiced by most people.

If monogamy were "instinctual" rather than "learned," it would not require elaborate social sanctions to enforce.

Since monogamy has never been an important part of human behavior and women are not "provisioned" by men in most cultures, then the earlier theory is invalid.

Some alternative proposals about non-estrus include:
1) Allowed human females to bond with more than one male.
2) Allowed human females to refuse mating when ovulating.


Non-human primates -no vocal cords for "human speech" but are able to use sign language.

Speculation that it was our larger range for gathering that may have resulted in human speech. The ability to explain something that happened in the past or might happen in the future might have been selected for with larger home range. Gatherer/hunter groups often bring back information about resources and dangers to the group to share.

These have been some behaviors that we see among non-human primates that have important implications for human origins. Many of these behaviors play crucial roles in the theories of human origins.

Of the many aspects of non-human primate behavior that seem to fascinate us is the idea of their communication. In recent past few decades debates have raged about the level of their abilities.

Communication, particularly our ability to create and use symbols, is the core of our culture, and thus at the core of our humanity. With non-human primates it has for some been at the core of our fears regarding these animals and our evolutionary closeness to them.

Communication has four aspects: signal, motivation, meaning, and function.

Signals are is the actual form of the communication act.
- the yell, the stare, the baring of the canines, the stink, or somethng else. You can describe and analyze a signal.

Among primates, signals can be made in any of four modes: olfactory, visual, auditory, and tactile.
The 4 modes can be ranked in terms of the strength or immediacy of the message.
Olfactory signals are odors, aromas, or stinks - something that is intended to be smelled. They are used to convey gentle warning or invitation, but not used to convey strong emotions, like love or anger. Among strepsirhines, however, olfactory signals are used for stronger messages.

Visual signals are something an individual does with its body or surroundings that is intended to convey a message. Things like staring, yawning, baring the canines, raising the tail, stamping the feet, shrugging the shoulders, or shaking the head are all visual signals.
For most primates, visual signal lie between olfactory signals and auditory signals in strength.
Color signals rank with olfactory signals as being relatively weak.

Auditory signals involve some use of sound, such as screaming, smacking the lips, whining, grinding the teeth, or barking. Usually, auditory signals are stronger than olfactory or visual signals.
Auditory signals have an advantage in that they can be perceived by a large number of receivers at the same time, even if those receivers were not initially paying attention to the individual giving the signal.

The strongest of all signals are tactile signals. Tactile signals involve one individual touching another in some manner, such as grooming, caressing, hitting, licking, or biting.

Of course, these 4 modes of communication can be combined in a variety of ways. A charging display (visual) can be combined with a yell (auditory) to provide a clearer, and to some extent stronger, message.

Motivation is the reason the individual is giving the signal. A motivation can be an emotion or feeling, or it can be a more complex message. Anger, lust, hunger, and fear are all possible motivations.
Motivation is one of the more abstract factors of communication. It is difficult to judge the emotional state of a particular individual without some level of ambiguity. Usually, the motivation of a signal has to be deduced from the context in which it's given, and its meaning.

The meaning of a signal is its interpretation by the receiving individual. We determine what the meaning of a given signal is by watching the reaction of the individuals that receive it. Again, the context in which a signal is given, received, and acted upon is important in trying to decipher an signal's meaning.

A signal's function is the evolutionary advantage, in terms of fitness, to having the signal as a component of the individual's behavior. The function is what the individual gains from the signal in an evolutionary sense.

Call systems vs language

In one sense, human language is simply a complex communication system. The calls, gestures, and facial expressions of non-human primates (and perhaps other animals) are also complex. The question then becomes, what is the difference between human language and the communication systems of non- human primates. How can we distinguish between the two?

A simple key is the idea of the symbol vesus the idea of a sign. Signs carry their own meaning and convey reality directly to the perceiver.
But symbols carry meaning for something else. They are intermediaries and they are abstractions from reality.

signs vs. symbols

Symbols are the basis of language.

Multi-level structure of language

Language is a multi-levelled system. Phonemes are basic elements of sound; morphemes are elements of meaning; syntax and grammar are rules for combining morphemes; and the sentence can be thought of as a complete message unit.

In comparison, communication systems do not have as many levels. Certainly, they have phonemes and morphemes (sound or the equivalent, and meaning). Whether or not they have syntax is debatable, and they certainly don't have a level comparable to the sentence.

Language is designed to be an open system, in that it is designed to allow the production of combinations of meanings to produce something new. Communication systems are closed systems - they are designed to express a well-defined set of meanings.

Language is highly arbitrary and culturally determined. The word for any given meaning varies enormously over the spectrum of human cultures. Non-human communication systems are less arbitrary and usually do not vary between groups.

An example of the ways in which a communication system is not arbitrary is that across all known animals that make noise, a quick, high, sharp sound means danger. Conversely, a low, sustained sound is reassuring.

Humans do have a communication system that for the most part stands beside language. This is a system of gestures and vocalizations referred to as paralanguage and kinesics.
Paralanguage consists of noises and changes to the character of the voice that are used while speaking. These carry information, but not in as precise a way as actual language.
One aspect of paralanguage is voice quality. We use a slow pace with very little change in pitch when we are bored and a faster pace with more change in pitch when we are excited. With control of rhythm, pitch, jerkiness, resonance, speed, and other qualities of the voice we can convey a lot of information about our emotions and attitudes.

Another aspect of paralanguage is vocalizations. Several vocalizations, like laughter, yawning, coughing, screaming, or growling exist, which convey information about emotional and physiological states.

Kinesics is the scientific terms for what we might call "body language". We use facial expressions, postures, motions, and movements of our hands to convey information. Kinesics are often complementary to speech.
Paralanguage and kinesics vary from culture to culture, but are much less variable than language.

Ape language studies

Most people familiar with communication systems agree that humans have language, and that all the primates up through monkeys don't have language. It is also thought that apes don't have or use language in the wild. Research has demonstrated that monkeys are incapable of using syntax correctly or forming a sentence. This issue is still undecided for apes, and is hotly debated.

The first experiment with ape language was trying to teach a chimp to actually use human spoken language. One experiment of this type was carried out by a husband/wife team named Hayes, using a chimp named Viki. Viki was raised as if she were a human child. Eventually, viki learned a few hoarse sounds like "cup", "mama", and "papa", but that was it.
So, the conclusion was that a chimp does not have the ability to use human spoken language.

The next experiment was conducted by the two psychologists, the Gardeners, and eventually Roger Fouts, who figured that even though a chimp is limited by its vocal apparatus, it might be able to communicate using a different system. So, they decided to teach a chimp named Washoe to use ASL or AMESLAN. AMESLAN is short for American Sign Language, which is used by many deaf people.
This experiment was much more successful. Washoe learned to use at least 132 signs correctly. This experiment has been repeated a few times. The master of AMSLAN is Koko, a gorilla, who has learned over 700 signs by now.

One of the most interesting ape language experiments was conducted at the Yerkes Primate Center by Susan Savage-Rumbaugh. They started with a chimp named Lana who they taught to communicate using a large computer input device. After analyzing the results Rumbaugh concluded that apes were actually able to learn abstract communication skills.
Among their questions is whether apes could spontaneously learn symbols, and work with Kanzai, a 2.5 year old bonobo and his 11 month old half sister suggests they can. They were never directly involved in the training sessions with their mother, but were simply present when she was trained.

These researchers all assumed that the chimps were really learning to communicate, but there is a critic. Herbert Terrace raised a chimp named Nim Chimpsky (a play on Noam Chomsky, a famous linguist), and taught him AMSLAN. Terrace video taped all his training sessions and studied them thoroughly. He concluded that Nim was actually not using AMSLAN as language, but was really just responding to cues provided, often unconsciously by the trainers. He explained it as a case of the "Clever Hans" problem.

The evidence has been debated back and forth for years. One problem may be that apes have species and individual differences in the extent to which they can use language. Most people feel that Koko is in fact using something nearly on the level of human language. The evidence for chimps is more tenuous, and it may be the Nim and even Washoe were really not using language on a human level.

Additional issues relate to the creativity of symbols and whether they can be taught by one ape to another. Some evidence from both the Washoe and the Lana studies suggests it is possible.

At any rate, no non-human primate language resembles human language communication and its complexity. We should be cautious about anthropocentrism, but symbolic communication is a defining characteristic of our species. Its development parallels many of our other evolutionary changes.

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