revised, 04/23/12

Have you got your project approved and have at least two recent references? At least one of these must be published in a scientific journal. Check the news items for recent reports on primate aggression.

Aggression and related topics

See the notes from last year for a more detailed overview. One main point is that aggressive behavior stems from many different sources and has several different levels of cause -- genetic, biochemical, including neurotransmitters (e.g. serotonin) and hormones (e.g. testosterone, cortisol) as well as social -- including protecting young, mate selection, competition for resources, and xenophobia (fear of strangers). Social (and cultural) factors may also serve to moderate aggression and as in the bonobos, over time social factors such as female resistance to harrassment might reduce levels of aggression via sexual selection.

Another perspective is the effect of early stressful experience on aggression -- monkeys, baboons, orangs and other primates including humans? Harlow many decades ago, and ongoing research today, all point to early social experiences impacting juvenile and adult behavior in regards to aggressiveness and many other psychological factors.

Cooperation, dominance, and aggression--much observed ape aggression is mediated by hierarchical rank or dominance of the participants-- agressor and aggressed. Much of this aggression in fact seems to serve maintaining or changing of hierarchical ranks.. We've seen this most obviously in dominance battles in orangs, baboons, and gorillas. Chimps have a more cooperative, political slant on hierachical control but can be extemely violent, e.g. rise and fall of Frodo (Return to Gombe video, DeWaal's account in Chimpanzee Politics (Family of Man video notes) . Bonobo females maintain a degree of hierarchical control via bonding, which male bonobos, unlike cousin chimps, seem to lack.

Depending on species, these dominance issues directly (chimp) or indirectly (orang) relate to mate selection and control.

Return to Gombe & Family of Chimps video (we saw only one of these.)

De Waal wrote his "Chimpanzee Politics" based on these Arnhem zoo chimps in the "Family.." video. One major conclusion is that aggression can serve to enhance bonds among group members. See notes. Similar aggression among male chimps was seen in the recent Goodall video. The attacks on the overthrown leader were limited here as Frodo, even though weak, could escape into the surrounding forest unlike the zoo situation.

Ape aggression

Recall the instances in the videos:



Read Wrangham and Peterson's introduction and chapter "relationship violence" for insight into our close relatives dark side: Male orangs "raping" females, male gorillas killing infants to encourage their mothers to go off with them, chimps harassing and intimidating reluctant females, even their siblings.

Why so little bonobo violence?

In addition to the three factors above, the females but not the males seem to be far more cooperative. When a female (or her son) is in trouble with another male, the other females tend to support the mother against the aggressor. This cooperation may be due to food availability compared with female chimps foraging on their own. If deWaal was right in Chimpanzee Politics, the idea that aggression may play a role in bonding in common chimps becomes interesting in regard to bonobo males.

Finally and speculatively, it is possbile that the early experiences of the bonobo juvenile males have less of the stressful "challenges" that increases the probability of more aggressive and violent responses to insults. See Nisbett and Cohen's discussion of this in regard to human males. Maybe experiences modify bonobos biologically to be less aggressive?? See Responsive Brain notes and Nisbett's work on "cultures of honor" in humans.

Gorilla violence

The usual story is that gorillas are peaceful unless attacked, contesting for females, and in occasional reports of infanticide in trying to "attract" females. Recently we have read news reports of male adolescent gorillas escaping from zoos and aggressively attacking humans. See Joe and one of his victims. Maybe Mighty Kong's revenge? We also read about the vicious chimp attacks on humans in the US and Africa. FInally there are the stories about orangutan males giving unwanted sexual attention to females of various species-- was Mr Kasasi thinking of more than a "smooch" with Julia?

Human aggression

We share many relevant traits with chimps including male cooperation, territoriality, fighting for food and mates. We are however even more effective with extensive tool use and progressive development of weapons, better planning and expliciting teaching of warfare. We also have long memories, enhanced by "mind tools" (language) that at times may foster revenge.


Read about the Nisbett and Cohen (1996-9) research about culture, violence, and hormones. Should nonhuman primates have similar effects? (The Scientific American paper is no longer available online.)

Here is a brief exerpt:

"Southerners favor violence in general no more than other Americans. They differ from northerners mainly over the use of force to protect home and property, to respond to insults and to socialize children. Our research shows, for example, that southerners are more likely to think it justifiable to kill to protect one's house. They are more likely to take offense at an insult and to think violence is an appropriate recourse. And they are much more inclined than northerners to say they would counsel their child to fight a bully rather than reason with him.

The differences go beyond attitudes. We conducted an experiment in which an accomplice insulted a college student by bumping him in a narrow hallway and swearing at him. (The students had agreed to participate in a study but were misled about its nature and were given no clue that the corridor incident was staged.) Northerners tended to shrug off the episode. The angry faces of southerners revealed that they did not take it so lightly. Moreover, their cortisol and testosterone levels--but not those of northerners--surged after the insult, which suggests stress and preparedness for aggression."

As it is very unlikely there are significant genetic differnces between "northerners" and "southerners" , these differences seem to me (JL) a result of differential socialization. Could this be an important part of the difference in aggression between bonobos and common chimps? Read their book online.

Culture of Honor: The Psychology of Violence in the South
by Richard E. Nisbett, Dov Cohen. 126 pgs.