notes on aggression

aggression: a fundamental characteristic of animal life

"I view aggressive behavior as a fundamental characteristic of all animal and human life, but I also believe that this trait cannot be understood in isolation from the powerful checks and balances that evolved to mitigate its effects." DeWaal, 1989, p.2)

aggression and relation to dominance

It is reasonable to distinguish aggressive behavior from dominance behavior. Dominance factors vary according to species; it also differs between and within sexes. (See below.)

difference between dominance and aggression

(All quoted from Mazur & xxx (1977; BBS in press)

"An individual will be said to act aggressively if its apparent intent is to inflict physical injury on a member of its species. An individual will be said to act dominantly if its apparent intent is to achieve or maintain high status -- i.e., to obtain power, influence, or valued prerogatives -- over a conspecific. Rodents typically dominate aggressively, but that is not true among the higher primates (Mazur 1973)"

(But note there are exceptions.)

"People in face-to-face groups form themselves into fairly consistent status hierarchies. Usually ranks are allocated cooperatively, but sometimes people compete for high rank in dominance contests where each contestant tries to outstress the other until one concedes, accepting the lower rank. We propose that high or rising testosterone (T), by encouraging dominant behavior, induces men to compete for high status."

"The experience ofwinning or successfully defending high rank boosting T, which in turn encourages more dominant behavior. The experience of losing depresses T, encouraging a switch from dominant to deferential behavior. This mechanism explains the momentum associated with winning or losing streaks."

factors in dominance

aggression, contests, maternal support and family connections, ability to form coalitions, size, resources (food sharing to information)

but are humans and some of our close relatives --"specialized" for aggression?

All large apes are suffiently intelligent to "amplify" the extent of aggressive tendencies via cunning, weapons, social skills, etc.

neoteny extends immaturity hence; effects of experience on behavior

(Recall data from Gould, 1977, showing that humans take many years longer to become sexually mature and attain full growth than do our closest primate cousins.)

good memory facilitates "feuds"culture and supporting brain structures enable war

Planning ahead is necessary for any serious warfare. Revenge so much a part of civil wars is a consequence of memory and planning.

biological foundations of aggression

The only really important point, here, I think, is that slight genetic changes might translate into significant behaviorial ones-- much like "human Growth Hormone" differences.

hormones: direct and indirect

Infant males show more anger and most reports of development show males engaging in far more aggressive behavior than females in humans and most primate species. Testosterone is a likely suspect here, both indirectly as it is instrumental in developing size and strength, but in mature individuals may somehow contribute to dominance or reflect it. (See Mazur et al, 1997).


Some research suggests differences in serotonin moderate aggressive behavior; higher concentrations associated with less aggression.

non-human ape aggression

W&P summarize three patterns of male violence in each of orang, gorilla, and chimp societies. These are not random acts of violence, but specific patterns that make sense in the particular social context and further the genetic interests of the violent males in different ways.

Humans share in some of these patterns; whether as a specific genetic or cultural adaptation remains unclear.


There are probably important differences in aggressive behaviors within a group and between groups and certainly other species.

Often within-group aggression is short-circuited by dominance relationships and reconcilation tactics.

In all cases, however --with perhaps the exception of insane human killers[1] -- we can bet that the outcome of aggression tends to increase the probability that the aggressor's genes get into the next generation.

increased fitness

competition for resources

Goodall (1990) describes the vicious attacks and killings among the various groups of chimps she observed where males, females, and infants of groups where decimated completely. "Suddenly I found that under certain circumstances they could be just as brutal (as humans)...The intercommunity attacks and the cannibalism were a different kind of violence altogether " p. 109 (than common in-group aggressive displays and fights where little actual damage occurs.)

competition for mates

male competition amongst themselvesinfancide

In some species the males will agressively attack other males and kill off infants presumably to make the females receptive sooner and further the conqueror's genes.

sexual coercion of females

Male chimpanzees and orangutans engage in intimidation and harassment of female, perhaps with the objective of controlling them at estrous.


Fear of strangers, especially males, may lead to attack.


No surprises here! Recall the "attack" scenes when chimps saw the fake leopard or lion.

protect one's offspring

Even females may become aggressive under these circumstances.

dispersal of individuals

Maturing individuals must find new groups or form their own. This serves both the interests of the parents' and those of the species. Aggressive behavior may even be seen in the weaning process as a mother prepares to nurse a forthcoming infant by driving off her five year old older offspring..

reduction of frustration-induced tension

Perhaps overrated by social psychologists, the frustration-aggression hypothsis probably has some truth to it.

increase social bonds

In any social group there are sources of tension and mechanisms for dealing with that tension -- from fighting to death to more subtle contests, alliances, and threats. Reduction of tension --of value on its own -- may also have a positive effect of increasing group cohesion and bonding among the the more aggressive individuals.

"In primates, however, major fights are followed by a wave of grooming and other friendly contacts among the members of a group. It is conceivable that with such mechanisms in operation, mild antagonism does not disturb bonds, but actually makes them stronger.(DeWaal, 1989, p.15)"

This seems particularly true for male-centered species like chimpanzees where females, not males, leave the home group when mature.

De Waal (1996) summarizes research with children suggesting natural resolution to fighting has a more positive outcome in regard to subsequent interactions than does fighting interrupted by adults.

In humans, consider the function of "initiation rites"--including hazing, boot camp, etc.

sources of tension (include the above situations)

feeding in unnatural settings

colonies/zoos/provisioning by Goodall

DeWaal (1982, p.22) notes that major fighting at the Holloman Airforce Base in New Mexico (a 25 acre open enclosure) took place at feeding time because of lack of facilities for separating apes --some of whom tried to hog all the food.

(See some of this in the Kortlandt experiment Nature video with grapefruit.)

In natural settings there is little competition for food; feeding is done in small groups. More than 1/2 a chimp's time is spent foraging and boredom increases in these unnatural settings.

dominance relationships

sexual encounters

See "Family of Chimps" video for example.

behaviors for reduction of tension

gentle touching, grooming, embracing (e.g. Harlow, Mason, 1965)

Sexual activity may also be important in this regard for some species; see deWaal (1989) on the bonobos. What about humans?

related skills

facial distinctiveness/recognition

Each facial expression conveys a particular mood and is accompanied by vocalizations. This goes to explain the brain specializations reflected in PROSOPAGNOSIA (See the French woman in the "Brain" video.) This is also related to the general concept of "kin recognition."

social communication skills

DeWaal (1982) reports extensive individual variation p.34

the extended hand gesture

It is the most common hand gesture in the colony...depends on the context. The apes use it to beg for food, for bodily contact, or even for support during a conflict. Wheh two apes confdront each other aggressively, one of them may hold out his hand to a third ape. this gesture of invitation plays an important role in formation of aggressive alliances, or coalitions: the politiacal instrument par excellence. (p.36)

the playface, grin, & beg --found everywherecoalitions

in escalating conflicts, chimps offer systematic support to specfic other chimps

reconciliations occur soon after conflict, e.g. kissing

contacts between opponents after a conflict are much more intense than contacts in other situations, kissing being the most characteristic behavioral feature. (DeWassl, 1982,p. 41)

"About 40% of the time opponents contact each other within half an hour of their aggressive distinct geture is the outstretched arm and open hand, which chimps use to beg for body contact. They also show more eye contact, yelping, and soft screaming...most important there is much more kissing in this situation., p.42, 1989)....conflicts are less often revived after friendly body contact betaween antagonists. p.44

evidence for intentional communication and awareness of others

sexual encounters between lower males and females. See "Family of Chimps" video.

rational behavior

we use reason and thought for the ability to make new combinations of past experiences in order to achieve a goal. In their SOCIAL application of reason, chimpanzees are truly remarkable.

dominance-a social mechanism

Dominance hierarchies tend to reduce serious conflicts by enabling each individual to assess strength & weakness of potential competitors without actual encounters.

coalitions determine male dominance

Males chimps grow up together, develop skills at forming alliances, and friendships that may be called into play in determining dominance. Size also plays a role.

males physically dominate females

(more in natural setting)

female-female relations

based on age & "personality' (p.185) female-female conflicts extremely rare (1/20 that of m-m)

sexual activity--"pan satyrus"

males initiate courtship (DeWaal (1982) reports several matings/day)

mating is not random

male hierarchies

High-ranking males are intolerant and chase lower ranking animals from estrus females and will attack him or his mate. (DeWaal, 1982, p.168). See Family of Chimps video.

female preferences

Females are wary of mating with lower males when dominant males are near but may accept or solicit offers at another time and place.

young nursing chimps (2-3 years) harass mother during mating

little intercourse between siblings, and between offspring & parent

Pusey (1980) reports females reject old and familiar male advances since they (f) are unable to know their fathers. They prefer mates from another group.

males--especially dominant ones-- may be tolerant & protective of infants

(Family of Chimps video)

[1]And I expect some grotesque just-so story can be fabricated here, too!