Primate Rumor: Gorillas eat meat?!?

I recently heard from a colleague that a rumor is circulating about gorillas eating meat. My initial reaction was to start laughing, and my latter was to start researching. I found the source of the rumour, and was disappointed to find that gorillas have been misrepresented. So, before anyone jumps on the carnivorous bandwagon let me be clear in saying that this is preliminary research focusing on Bonobo (Pan paniscus) meat-eating behavior, and is not strong evidence for gorillas (Gorilla gorilla) eating meat.

My search first led me to a National Geographic (2010) article entitled “First Proof Gorillas Eat Monkeys?” which highlights some of Hofreiter et al.’s (2010) research results (reviewed below). The end product of this National Geographic article is a sensationalized depiction of Gorillas eating meat which is based on very preliminary, and potentially problematic evidence. The article suggests in its title that “proof” exists in science, which is language most scientists carefully avoid. After outlining what they consider to be a major finding in Hofreiter et al’s publication, that because animal DNA is present in gorilla feces gorillas eat meat, the article quotes Grit Schubert (one of the study’s authors) as saying “[t]here may well be more mundane explanations for the surprising finding—explanations that’d have to be ruled out before gorillas could be reclassified as meat-eaters.” Although these other explanations may be mundane they are certainly more likely than the hypothesis that “gorillas might have a secret meat habit—scavenging or hunting discretely.”

The actual focus of Hofreiter et al.’s (2010) study, Vertebrate DNA in Fecal Samples from Bonobos and Gorillas: Evidence for Meat Consumption or Artefact?, was the DNA content of bonobo feces, with gorillas included as a control due to their folivorous diet. The accidental finding that vertebrate DNA was also found in the gorilla fecal samples has however become the focus of media reporting. In recent observations of some bonobo populations it was found that they consume more vertebrate prey than previously believed. Hofreiter et al. investigated the extent of bonobo meat consumption using PCR
amplification of vertebrate mitochondrial DNA (mtDNA) segments extracted from feces.  Hofreiter et al. found evidence for the consumption of a variety of mammals in 16% of the samples tested. Duiker and monkey mtDNA was also found in the gorilla feces, however only 5 of the 78 fecal samples studied had this result. Hofreiter et al. argue that their results are due to a variety of possible and mutually non-exclusive explanations, including meat eating behaviour and contamination. Similar to bonobos “the gorilla population investigated (for which very little observational data are as yet available) may occasionally consume small vertebrates. Although the last explanation is speculative, it should not be discarded a-priori given that observational studies continue to unravel new behaviors in great ape species.” However, “results obtained exclusively by molecular studies may be prone to misinterpretation due to contamination” (especially in the case of the gorilla samples). Furthermore, “[f]urther studies investigating the reliability of DNA sequence data from feces and the development of methods to distinguish truly endogenous DNA from environmental contamination are necessary before such analyses can be used as sole evidence for novel behavior.” In the National Geographic article Schubert (one of the study’s authors) was quoted as saying that “[t]here’s plenty of opportunities” for adding mammal DNA to gorilla scat after the fact…I don’t really think they’re eating meat.”

I too remain a skeptic and await more research on the topic. It is apparent from examples like this that often media reporting of science publications can be misleading and result in the spread of inaccurate rumors. It is therefore very important to be a critical consumer of popular media.

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