Primate sex crime?

October 13, 2014 10:42 AM

From lay reading and popular science I understand that male chimpanzees are aggressive and extremely political. My question is, is the killing of adult female by adult male chimpanzees a thing? Is it a hazard of sexual contact for the female? Has it been observed, and if so, are there any explanations? Notes: I understand anthropomorphic concerns are not relevant framing for understanding ape sex. I have no difficulty with any of the terms used here: Primate Ifo Net. I've had a quick look through here: Sexual Coercion in Primates and Humans, and it doesn't answer the question.

I'm making a difference here between violence clearly having to do with access to resources or maintaining status, which would have happened regardless of the gender of the attacked, and violence where sex and/or gender appears to be the determining factor.

I'm not much for evolutionary psychology, and I have no sort of religious viewpoint whatsoever. I'm interested in whether this sort of killing is an observed phenomenon among primates. Oh, and, as far as aggression and social structure goes, I know there's a difference between bonobos and chimps.

posted by glasseyes to Science & Nature (5 answers total)

To my knowledge, there has never been an observed case of this happening among wild chimpanzees. Chimps certainly do kill each other, but not over sex. I hope an actual primatologist will correct me if I'm wrong (I'm an evolutionary anthropologist but don't specialize in primate behavior).
posted by baby beluga at 1:22 PM on October 13, 2014 [1 favorite]

Best answer: Primatologist here, but not a chimpanzee person. "Conflict and Cooperation in the Study of Wild Chimpanzees" (pdf) is a good review of chimpanzee behavior. Female chimpanzees definitely experience aggression and violence in the context of sexual coercion from males in their social group. When females are in estrus, they are the focus of a lot of attention and generalized aggression, which can have pretty significant effects on fertility, stress, health, and so on. Infanticide is also pretty well documented in chimps, and that represents a SIGNIFICANT blow to females because of lost parental investment. That can be argued to be a kind of sexual coercion, since ostensibly infanticide brings females back into estrus.

In that Muller and Wrangham article, they state "A detailed summary of observed intercommunity attacks on adults and adolescents is reported in Wrangham and Wilson (2003). These include nine killings at Gombe (two females)." That paper is available here: Intergroup Relations in Chimpanzees (pdf). Most of the lethal aggression they report is between males of adjacent communities, and generally does seem to be related to resource and territory control. There's almost always an imbalance of power when males attack other males - three against one, or similar numbers. That Jane Goodall "Behavior of Wild Chimpanzees" book from 1986 that you linked to is one of the citations for lethal aggression of males against females:

Remarkably, however, males often attack females, and these attacks can involve considerable brutality, especially if the female has young offspring (Goodall 1986; J. Williams and A.E. Pusey, submitted manuscript). At Gombe, males attacked stranger mothers in 76% of encounters (Goodall 1986). In some cases, males focus their attacks on the female’s infant, which they may kill and eat (e.g., Bygott 1972, Watts et al. 2002). At other times, however, males appear focused on attacking the mother rather than the infant [e.g., many cases at Tai (Boesch & Boesch-Achermann 2000)]. Attacks on stranger females can result in severe wounds and, in at least one case, death (Goodall 1986).

If I'm recalling correctly, that was an instance of males on a border patrol who come across a solitary female (or maybe female with infant) and attack her. I couldn't find the Williams and Pusey article that they reference, but there is some cool research about female coalitionary aggression here: "Chimpanzee Violence: Femmes Fatales."

There was also just a recent review of chimpanzee aggression in Nature, "Lethal agression in Pan is better explained by adaptive strategies than human impacts." (here's the abstract, let me know if you want the PDF). It's the next part in a long debate about whether or not chimpanzee violence is natural and evolutionarily linked to human violence, or if it's the result of human interference and habitat degradation. At any rate, all their reported instances of lethal aggression towards female chimpanzees comes in the context of males from one community attacking females from a different community, sometimes with an infant:

Intercommunity killings mainly involved parties with many males (median = 9 males, range: 2–28, n = 36 cases with known numbers of attackers) attacking isolated or greatly outnumbered males or, more often, mothers with infants (median = 0 males, range: 0–3, n = 30; median = 1 female, range: 0–5, n = 31). For 30 cases in which the number of adult and adolescent males and females on each side were known, attackers outnumbered defenders by a median factor of 8 (range: 1–32; Extended Data Table 7). Most intercommunity killings thus occurred when attackers overwhelmingly outnumbered victims... Male chimpanzees killed more often than females, and killed mainly male victims; attackers most frequently killed unweaned infants; victims were mainly members of other communities (and thus unlikely to be close kin); and intercommunity killings typically occurred when attackers had an overwhelming numerical advantage.

So I guess that is also going to be distinguished from the sort of aggression you're interested in. But it is still interesting! Keep in mind, though, that this is still a relatively controversial set of articles (Brian Ferguson against the article, Michael Wilson in response).

If you want anything in particular that you can't find a copy of online, let me know and I'll try to get it to you. I hope those articles give you a little more to go on. It's an interesting topic!
posted by ChuraChura at 6:28 PM on October 13, 2014 [7 favorites]

Despite it's horrible title, I found the book Demonic Males to be really interesting and not as sensationalist as the cover would suggest. It's written by an Anthropologist (Richard Wringham, who ChuraChura mentioned above) and a science writer so it's really accessible to a non-specialist, but still based in solid research and field work. The connection between violence and sex in Chimps is directly addressed in the book, and it is easily one of the most fascinating things I've read.

It's been a few years since I read it, but there was a pattern described where some lower-status males would isolate and beat a female into sex. I don't think killing happens as often, but sex and violence are linked in other ways, as well.
posted by ohisee at 12:59 AM on October 14, 2014

Response by poster: So it looks like while coercion and infanticide are pretty common for chimps out-and-out sexual murder not so much? Re the word murder, it's really hard not to keep slipping into anthropomorphism thinking about this question, and of course there is often an implicit desire to have human behaviour illuminated by these sorts of studies.

Thanks all, and ChuraChura, that is an amazing answer, I'll be busy for a while going through the links. ohisee, I have read Demonic Males and yeah, it's really interesting about the politicking that goes on between chimps.
posted by glasseyes at 8:42 AM on October 15, 2014

Response by poster: Eight against one, huh.
posted by glasseyes at 8:48 AM on October 15, 2014