“Do chimpanzees in the wild want to kill others? Is murder common among wild chimpanzees? Do male chimps (and their cousin male humans) have “killer” “demonic” instincts towards their fellows? If you look at the data, the answer to these questions is a resounding NO! But these beliefs are “gospel” in much of popular science. This misinformation colors our view of humans and human nature. What are the ramifications?”

This was the opening paragraph of a recent blog by Dr. Darcia Narvaez on the Psychology Today website. Dr. Narvaez, an Associate Professor of Psychology at Notre Dame University, decided to tackle the question of whether or not male humans and chimpanzees are “genetically violent” – a poor choice of terminology, but I know what she’s driving at, and I’ve got a fair amount of experience in this area. So, I decided that I would take a few minutes and write up a response to Dr. Narvaez’s assertions to see if we can’t set the record straight in this regard.

The best place to start is with her opening paragraph, and we’ll look at each question and the wording she uses to see if her conclusions hold up:

“Do chimpanzees in the wild want to kill others?” I call this the Dr. Doolittle question. This question is asking what the desires and intentions are of an animal that doesn’t possess the power to communicate in a spoken language [at least not one humans understand at this point]. Therefore, the question, at its essence cannot be answered. However a few clearer, related questions can be answered:

1) Do chimpanzees in the wild avoid attacking others?
2) When chimpanzees in the wild attack others do they exhibit behaviors associated with excitement?
3) When chimpanzees in the wild attack others do they kill them when possible, or attempt to do so?

No matter how you analyze the data from field notes, to video to personal observation (been there, seen that) the answer to the three questions listed above are:

1) No, chimpanzees in the wild do not avoid attacking others if they appear to have a numerical advantage over their rivals. Goodall suggested this in her classic volume on the Gombe chimpanzees and it has since been supported through observational (Sherrow & Amsler, 2007) and experimental (Wilson et al, 2001) work.
2) Yes, chimpanzees in the wild exhibit behaviors (and physiology) associated with excitement when they attack others. Their hair stands on end in what ethologists call pyloerection and they run around screaming and shouting, often displaying and seeking each other out for reassurance (personal observation).
3) Yes, when chimpanzees in the wild attack others they kill them when possible, or they attempt to do so. There have now been reports from every major chimpanzee research site, with long-term habituation of either lethal aggression or attempts to commit acts of lethal aggression (Boesch et al, 2007; Sherrow, in preparation; Wilson & Wrangham, 2003).

“Is murder common among wild chimpanzees?” I call this the anthropogenic question. Chimpanzees may kill each other, but murder is a wholly human act, it implies intentions, motivations and emotions that we cannot attribute to even our closest living relatives. As for the question of whether or not they kill each other, see #3 above.

“Do male chimps (and their cousin male humans) have “killer” “demonic” instincts towards their fellows?” I call this the disassociated question. “Killer” and “demonic” need not be inseparable in our understanding of the two words. A soldier who kills in defense of her/his country, or a police officer who kills in defense of victims of a violent crime are not considered “demonic”, yet they are killers by the strictest definition of the word. They are also something else – heroes. Killing, in most human societies, is not always bad, but depends on the context of the killing (Livingstone Smith, 2009).

Dr. Narvaez chose to use the term “demonic” because of a very influential and popular book that was published in 1996, Demonic Males: Apes and the Origins of Human Violence by Wrangham & Peterson. In that book the authors used solid data (science lingo for information) on the living apes to show that when violence and aggression occur in our non-human cousins, males are the primary actors. In other words, males in our closest non-human ape relatives; bonobos, chimpanzees, gorillas and orangutans are more violent than their female counterparts. To those of us who study apes, this book was not as surprising as it was a great job of compiling and synthesizing much of the known information about apes at the time.

One of the most controversial claims made by Wrangham & Peterson in Demonic Males, is one that has been made by Dr. Jane Goodall, DBE herself and has been supported with overwhelming evidence from across Africa (e.g. Arcadi & Wrangham, 1999; Boesch et al, 2007; Goodall, 1986; Mitani et al, 2010; Muller, 2002; Nishida, 1979; Sherrow & Amsler, 2007; Watts et al, 2006; Williams et al, 2008; Wrangham, 1999), chimpanzee males regularly patrol territorial boundaries and when possible attack and kill males and infants from other communities.

Dr. Narvaez, uses information from two books by Hart and Sussman (2009) and Power (1991), which she claims to show how the evidence for lethal xenophobia in chimpanzees, presented in Demonic Males is “paltry”. She even uses the arguments laid out by Hart and Sussman to establish her position:

“(1) Goodall reports a so-called raiding party in 1982 in which a female was chased and mildly attacked and her 4-year-old son was sniffed.”
– Dr. Narvaez does herself a disservice by using the term “so-called” in describing the report by Goodall from 1982. Dr. Goodall literally wrote the book on chimpanzee behavior.

“(2) A 35 year old male’s body was found in 1981. With no evidence, murder was inferred. Males rarely live past 33.”
– The body had been trampled with injuries that appeared to be from other chimpanzees. Beyond that, again, chimpanzees do not “murder”. While the average age for male chimpanzees at death is around 33 that includes males who die before age 15. Once males reach maturity, they can live into their late 30’s and 40’s in the wild.

“(3) “From 1970 to 1982 six adult males from one community disappeared at a Japanese study site in the Mahale Mountains of Tanzania, west of Gombe,” one by one over a 12 year period. With no evidence, murder was inferred. But lions are common predators of chimpanzees in that region.”
– While the attacks weren’t observed in those cases at Mahale, the males in question disappeared after intense territorial disputes between two communities and extremely loud and violent fighting sounds were heard before those males disappeared (Nishida et al, 1990). Again, “murder” was never inferred. As for lions being “common” predators of chimpanzees in that region, that statement is misleading. Lions regularly pass through the Mahale study area in western Tanzania and do prey on chimpanzees, however they are not common predators. Further, if lions were regularly eating chimpanzees in the region, we would expect to see a consistent rate of predation and it should be fairly evenly distributed between males and females (in fact, given that females are often alone, it should skew toward more females being preyed upon). Instead, the disappearance was of adult males, after intense territorial interactions.

“(4) Wrangham and Peterson misreport statements by Christopher and Hedwige Boesch, saying that they said “violent aggression among the chimpanzees is as important as it is in Gombe” whereas they really said, according to Hart and Sussman is that “encounters by neighboring chimpanzee communities are more common in their site than in Gombe and that this may lead to larger, more cohesive, group structure and a ‘higher involvement of the males in social life’-there is no mention of any violence or killing during these encounters” (p. 210).”
– This is just plain wrong. What Boesch and Boesch (1989) really said was, “The pressure of territorial fights could be another major factor. Encounters with neighboring communities are fairly common (29 encounters in 29 months in Tai’). It might well be that the larger a male group is, the higher is its chance to win such territorial fights and the higher is its chance of enlarging its territory and its access to females (see descriptions of intercommunity encounters in Gombe;Goodall,1986;Wrangham, 1975)…This increase in group cohesion may be related to an increase in territorial pressure from neighboring communities. Thus the probably higher rate at which strangers are encountered in Tai’ may have forced them to adopt a more cohesive group structure, which may subsequently lead to a higher involvement of the males in social life at the cost of tool manipulation (Boesch and Boesch, 1984b).” Territorial fighting, by definition, is violent.

(5) At the site Wrangham had studied since 1984, a male’s body was found in 1991 a few days after the troop’s males had been exchanging calls with another community. The researchers had not seen any violence, nor was there any in the 7 years prior or 6 years after the incident. With no evidence, murder was inferred.
– Again, this statement, like the last is wrong. First, the chimps name was Ruwenzori, not Ruizoni as Hart & Sussman claim (p. 210). He was named for the mountain range to the west of Kibale National Park, where he lived and his body was found four days after he went missing, after an intercommunity encounter (a shouting match) between his community and their neighbors to the south. The research team “…found his disintegrating body hunched at the bottom of a little slope. The trampled vegetation bore witness to a struggle that started upslope and careened downward, sometimes sideways, for fifteen meters or more. Ruwenzori’s body was bitten and bruised and torn. He died healthy, with a full stomach, on the edge of adulthood, on the edge of his range.” (Wrangham & Peterson, 1996. p20). This is substantial evidence that Ruwenzori was killed by other chimpanzees, not “no evidence” as Dr. Narvaez would have her readers believe.

It’s unfortunate that Dr. Narvaez didn’t take the time to dig a little deeper into this subject, or to use information from researchers who study chimpanzees. While I don’t think you have to study chimpanzees to understand their behavior, and that you can get a lot from the literature, I think that something can be said for first-hand experience. Once you witness lethal violence in chimpanzees, you are not likely to forget it. For those with strong stomachs I have attached a short video to this blog that will hopefully provide some understanding to the excitement and brutality involved when male chimpanzees stalk other chimpanzees and engage in lethal violence towards them.

By not going deeper into the argument, but instead using some of the data to support a position she already holds, Dr. Narvaez is being ignorant at best, and more likely irresponsible in her blog. When Dr. Narvaez claims, “…that our current cultures, societal practices and beliefs have created the violent humans we see around us. They are an aberration from our evolutionary heritage…That means we have ourselves to blame, not selfish genes, not evolution. And it means we can change the practices and beliefs that create our violent cultures.” She is stating a philosophical position that is admirable in some regard, but not defensible given the information out there on chimpanzees and humans.

The other day in my Human Evolution course I had my students go through an exercise of identifying and labeling the traits that make us human. We listed everything we could think of and then went through them all, crossing them off to get at the traits that were unique to humans. One of the traits the students came up with was “lethally xenophobic”, referring to the propensity of humans to attack and kill members of other communities, nation states, ethnic and religious groups. The students were quick to point out that that trait was not unique to humans, but like our chimpanzee cousins we form in-groups and out-groups, and like our chimpanzee cousins we are not kindly disposed to members of out-groups, or outsiders.

By ignoring what the scientific data tells us about ourselves and our closest living relatives, we are committing ourselves to an inquiry of ignorance that is doomed to failure. If we want to succeed in understanding violence and warfare, we must understand its evolution.

REFERENCES

Arcadi, A. C. & Wrangham, R. W. 1999. Infanticide in chimpanzees: Review of cases and a new within-group observation from the Kanyawara study group in Kibale National Park. Primates. v40 (2). p337-351.

Boesch, C. & Boesch, H. 1989. Hunting behavior of wild chimpanzees in the Tai National Park. American Journal of Physical Anthropology. v78. p547-573.

Boesch, C., Head, J., Tagg, N., Arandjelovic, M., Vigilant, L., & Robbins, M. M. (2007). Fatal chimpanzee attack in loango national park, gabon. International Journal of Primatology, 28(5), 1025-1034.

Goodall, J. 1986. The chimpanzees of Gombe: Patterns of behavior. Harvard University Press.

Livingstone Smith, D. 2007. The most dangerous animal:Human nature and the origins of war. St. Martin’s Press.

Muller, M. N. 2002. Agonistic relations among Kanyawara chimpanzees. In: Behavioural diversity in chimpanzees and bonobos. Cambridge University Press.

Nishida, T. 1979. The Social Structure of Chimpanzees of the Mahale Mountains. In: The Great Apes. Ed Hamburg, D. A. & McCown, E. The Benjamin Cummings Publishing Company.

Nishida, T. 1990. The Chimpanzees of the Mahale Mountains: Sexual and Life History Strategies. The University of Tokyo Press.

Sherrow, H. M. & Amsler, S. J. 2007. New cases of inter-community infanticides by the chimpanzees of Ngogo, Kibale National Park, Uganda. International Journal of Primatology. v28 (1):9 – 22.

Sherrow, H. M. In Preparation. The Testicle Targeting Hypothesis and Intrasexual Competition Among Male Chimpanzees. To be submitted to Behavioral Ecology & Sociobiology.

Watts, D. P., Muller, M., Amsler, S. J., Mbabazi, G., & Mitani, J. C. (2006). Lethal intergroup aggression by chimpanzees in kibale national park, uganda. American Journal of Primatology, 68(2), 161-180.

Williams, J. M., Lonsdorf, E. V., Wilson, M. L., Schumacher-Stankey, J., Goodall, J., & Pusey, A. E. (2008). Causes of death in the kasekela chimpanzees of gombe national park, tanzania. American Journal of Primatology, 70(8), 766-777.

Wilson, M. L., Hauser, M. D., & Wrangham, R. W. (2001). Does participation in intergroup conflict depend on numerical assessment, range location, or rank for wild chimpanzees? Animal Behaviour, 61, 1203-1216.

Wilson, M. L. & Wrangham, R. W. 2003. Intergroup relations in chimpanzees. Annual Review of Anthropology. v32. p363-392.

Wrangham, R. W. 1999. Evolution of coalitionary killing. Yearbook of Physical Anthropology. v42. p1-30.

Wrangham, R. W. & Peterson, D. 1996. Demonic Males: Apes and the origins of human violence. Houghton Mifflin.

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