It is the first of May, thus the time to award my Pick Of The Month award for April. There were 29 blog posts covering PLoS ONE articles aggregated on ResearchBlogging.org in April (and several good ones I saw that are not on the aggregator, thus not eligible for the prize). Just like last month, this was a fun exercise for me, reading all those excellent and interesting science blog posts. And several were really, really good, so the decision was not easy to make.
The post that really stood out for me this month was the one by Eric Michael Johnson who blogs on The Primate Diaries. In the post Male Chauvinist Chimps or the Meat Market of Public Opinion?, Eric discusses the PLoS ONE article Wild Chimpanzees Exchange Meat for Sex on a Long-Term Basis by Cristina M. Gomes and Christophe Boesch of the Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
The article demonstrates that male chimpanzees that share meat with females enjoy a greater reproductive success. The females remembered over long period of time which males shared meat with them and more readily mated with those males. From the Abstract:
Humans and chimpanzees are unusual among primates in that they frequently perform group hunts of mammalian prey and share meat with conspecifics. Especially interesting are cases in which males give meat to unrelated females. The meat-for-sex hypothesis aims at explaining these cases by proposing that males and females exchange meat for sex, which would result in males increasing their mating success and females increasing their caloric intake without suffering the energetic costs and potential risk of injury related to hunting. Although chimpanzees have been shown to share meat extensively with females, there has not been much direct evidence in this species to support the meat-for-sex hypothesis. Here we show that female wild chimpanzees copulate more frequently with those males who, over a period of 22 months, share meat with them. We excluded other alternative hypotheses to exchanging meat for sex, by statistically controlling for rank of the male, age, rank and gregariousness of the female, association patterns of each male-female dyad and meat begging frequency of each female. Although males were more likely to share meat with estrous than anestrous females given their proportional representation in hunting parties, the relationship between mating success and sharing meat remained significant after excluding from the analysis sharing episodes with estrous females. These results strongly suggest that wild chimpanzees exchange meat for sex, and do so on a long-term basis. Similar studies on humans will determine if the direct nutritional benefits that women receive from hunters in foraging societies could also be driving the relationship between reproductive success and good hunting skills.
Eric’s post adds another angle to the study, looking at it from the perspective of females:
It may be that females were reserving the early period of estrous for them and the more fertile period for males of higher rank. However, it could also be that those who demonstrated themselves willing to share were viewed as a better long-term investment. The bottom line however is that females were the ones calling the shots, and males understood that there were only two ways to prove they were serious.
Discussion continues in the comments section of the post as well, including comparisons between chimps and bonobos as well as, almost inevitably, to humans, thus placing the study in a broader context.
Congratulations both to Eric and to the authors of the article. I have notified the winners and their prizes are on the way. I hope you read Eric’s post and post a comment of your own, and then go to the article itself to read it and post comments, notes and ratings there as well.