Skip to main content

Male Chauvinist Chimps or the Meat Market of Public Opinion?

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American


Author's Note: The following originally appeared at Nature Network. It was subsequently selected as a PLoS ONE Pick of the Month, as a Finalist in the 2009 Quark Prize in Science and appeared in the 2009 edition of The Open Laboratory: The Best Science Writing on the Web (buy it here). You can still nominate entries for this year's edition until December 1, 2011.

From the introductions alone, you would have thought you were in a 19th-century gentleman's club enjoying cigars and brandy. "There's nothing like a prime rib dinner to boost a guy's chances of getting lucky," boasted ScienceNOWas he cleaned his monacle. The Daily Mailagreed with a harrumph, "As every Romeo knows, laying on a delicious dinner for two is one of the best seduction ploys." Chuckling along with a wink and a nudge, MSNBC added, "A savory meat dinner goes a long way, as in all the way."

Ostensibly, these articles were talking about chimpanzees, but it was made perfectly clear what they were getting at. Rupert Murdoch, naturally, got straight to the point. "The oldest profession isn't restricted to humans," FOXNews asserted, while The New York Post headline simply shouted "Chimpanzee Meat Market."


On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.


In other words, dating is just another form of prostitution and evolution proves that he that pays gets play. For some reason the barriers were down. Talking about chimpanzee sexuality allowed journalists to let loose and express views they would rarely utter otherwise. Evidently people got the message, if the comments on Slashdot are any indication. A rare case of maturity could be found at Nature's The Great Beyond which wrote that:

News that female chimps mate more frequently with male chimps that share their meat with them has prompted a slew of at best corny, at worst downright sexist, even lewd, headlines.

The main problem was that, while everyone else was busy giggling over these chauvinist fantasies, they missed the real meat of the story.

The study in the journal PLoS ONE, by Cristina Gomes and Christophe Boesch of the Max Planck Institute for Evolutionary Anthropology, finally answered a question that has intrigued primatologists for nearly two decades. Do female chimpanzees preferentially mate with males who share their hunting gains with them? This hypothesis was first suggested in 1994 by Craig Stanford and Jane Goodall when they found that the best predictor for whether males would engage in a hunt or not was the presence of females with sexual swellings (large, fluid-filled sacs indicating the estrous phase of their reproductive cycle). However, subsequent studies could not find any evidence that hunting resulted in direct fitness benefits.

According to a study by Mitani and Watts, females with sexual swellings only received meat on 23 occasions out of 68 attempts and, of those, just 14 resulted in matings. Only a third of all estrous females got meat when they tried for it. In contrast, males were almost four times as likely to share meat with another male involved in the hunt than with an estrous female. When meat was shared with an estrous female, only slightly more than half chose to mate with the male who offered it. The "meat-for-sex" hypothesis appeared to be flaccid. And yet, strangely, there were few sensationalist news reports touting evidence of bromance among our evolutionary cousins.

However, Gomes and Boesch suggested a different approach. What if females remembered the male who shared with them and chose to mate with them at a later time? Over a period of 22 months in the Taï Forest of Côte d'Ivoire the researchers recorded every case of meat sharing (both with estrous and anestrous females), noted who was sharing the meat with whom and identified all of the mating partners during the study period. They also measured grooming, sharing of additional food items and the number of times males assisted females in conflicts with other individuals. Their results indicated that:

[F]emales copulated more frequently with males who shared meat with them at least on one occasion, than with males who never shared meat with them.

The authors were able to eliminate all other variables as significant factors except for male rank, which was independent of meat sharing. The final conclusion was that females were expressing two mutually exclusive choices (see Table 1 below). The authors spelled it out plainly:

Male rank and sharing meat with females had independent effects on male mating success, indicating that females copulated more with males who shared meat with them and with males of high rank.

The larger story lay not in the fact that females preferred to mate with males who provisioned them, but that they were opportunistically shifting their mating strategies for their own reproductive interests. In earlier studies by Boesch at the same site it was demonstrated that 84% of undesirable advances were rejected by females (Stumpf & Boesch 2006; pdf here), promiscuous mating was reserved for the early part of estrous and that 93% of all copulations were terminated by females (Boesch et al. 2006; pdf here). Females chose who they would mate with, when they would mate with them and how long it would last.

Crucially, as Boesch also determined, ovulation generally occurred between five to eight days after maximum tumescence (when their sexual swellings were largest). By focusing on promiscuous mating in the early part of estrous, females were effectively ensuring that fertilization was less likely. In the later part of estrous females preferred a selective strategy and were much more likely to engage in "consortships" (where a female and male dyad would disappear for several days). This would ensure that the desired male ended up being the father of her child. As a result of these flexible strategies Boesch found that alpha male mating success fluctuated wildly, ranging from 67% to 38% over a 14 year period (Boesch et al. 2006; pdf here). These same shifting and opportunistic strategies have also been observed in populations at Mahale and Gombe.

Unfortunately, this study by Gomes and Boesch didn't measure when in the estrous cycle females chose to mate with males who shared their hunt. 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.

Rather than such hackneyed cliches as "Sex sells, even in the rainforest" (Cosmos) or "The way to a chimp's heart is through her stomach" (Wired) the real story was that female chimpanzees demonstrate flexible and opportunistic strategies to maximize reproductive success. Furthermore, because the sharing of meat was primarily with anestrous females and because there was no relationship between the amount of meat provided and the number of copulations, suggesting that this had any connection to prostitution or buying someone an expensive meal in order to "get lucky" was to completely miss the point. In all likelihood, females were using these exchanges to determine who would be the best potential father for her offspring over the long term. High rank has its advantages, but so does the guy who's willing to share.

Reference:

Gomes, C., & Boesch, C. (2009). Wild Chimpanzees Exchange Meat for Sex on a Long-Term Basis PLoS ONE, 4 (4) DOI: 10.1371/journal.pone.0005116

About Eric Michael Johnson

I grew up in an old house in Forest Ranch, California as the eldest of four boys. I would take all day hikes with my cat in the canyon just below our property, and the neighbor kids taught me to shoot a bow and arrow. I always loved reading and wrote short stories, poems, and screenplays that I would force my brothers to star in. A chance encounter with a filmmaker from Cameroon sent me to Paris as his assistant and I stayed on to hitchhike across Europe. Nearly a year later, I found myself outside a Greek Orthodox Church with thirty Albanian and Macedonian migrants as we looked for work picking potatoes.

After my next year of college I moved to Los Angeles to study screenwriting and film production. My love of international cinema deepened into larger questions about the origins of human societies and cultures. I entered graduate school with a background in anthropology and biology, joining the world-renowned department of Evolutionary Anthropology at Duke University to pursue a PhD in great ape behavioral ecology. But larger questions concerning the history and sociology of scientific ideas cut my empirical research short. I am now completing a dissertation at University of British Columbia on the intersection between evolutionary biology and politics in England, Europe, and Russia in the nineteenth century. In 2011 I met the economist and Nobel Laureate Amartya Sen whose work inspired my award-winning research.

My writing has always been a labor of love and a journey unto itself. I have written about the hilarity that ensues once electrodes are stuck into your medial ventral prefrontal cortex for Discover, the joy of penis-fencing with the endangered bonobo for Wildlife Conservation, and the "killer-ape" myth of human origins from Shakespeare's The Tempest to Kubrick's 2001: A Space Odyssey for Times Higher Education. My work has appeared online for Wired, PLoS Blogs, Psychology Today, Huffington Post, SEED, ScienceBlogs, Nature Network and a host of independent science related websites. I have appeared four times in The Open Laboratory collection of the year's best online science writing and was selected the same number as a finalist for the Quark Science Prize, though better writers have always prevailed. I am currently working on my first book.

If I am not engaged in a writing or research project I spend time with my young son, Sagan. Whenever I get the chance I go on backpacking trips in the mountains of British Columbia or catch the latest film from Zhang Yimou, the Coen Brothers, or Deepa Mehta. To this day one of my favorite passages ever written is from Henry David Thoreau's Walden where he describes an epic battle between ants in Concord, an injured soldier limping forward as the still living heads of his enemies cling to his legs and thorax "like ghastly trophies at his saddle-bow." Thoreau helped fugitive slaves to escape while he mused on the wonder and strange beauty of the natural world. Not a bad way to spend an afternoon.

More by Eric Michael Johnson