Photograph by Michael Poliza, National Geographic Stock

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Wild mountain gorilla in Bwindi Impenetrable National Park, Uganda (file photo).

Photograph by Michael Poliza, National Geographic Stock

First Proof Gorillas Eat Monkeys?

Mammal DNA in gorilla feces hints the big apes might eat meat after all.

Like the vegetarian who can't resist the occasional burger, the otherwise herbivorous gorilla might succumb to cravings for its evolutionary cousins, a new study hints.

While some zoo specimens are known to eat meat, wild gorillas eat only plants and fruit, along with the odd insect—as far as scientists know (see video of wild gorillas feasting on figs).

But a recent study found DNA from monkeys and small forest antelopes called duikers in the feces of wild African western lowland gorillas in Loango National Park in Gabon.

The discovery raises the possibility that gorillas might have a secret meat habit—scavenging or hunting discretely.

Gorillas Eating Insects That Eat Mammals?

There 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, said study co-author Grit Schubert, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

For example, gorillas are known to eat ants that scavenge the carcasses and bones of monkeys and other mammals. When gorillas eat the ants, they may also be ingesting—and later expelling—the mammal DNA in the ants' digestive tracts, the study authors speculate.

Another possibility is that the mammal DNA came from live monkeys or duikers that had been probing the gorilla feces for edible seeds or other leftover plant bits.

Or the mammals "might have just licked it, sniffed it, or peed on it," Schubert said.

"There's plenty of opportunities" for adding mammal DNA to gorilla scat after the fact, Schubert said. "I don't really think they're eating meat."

Gorillas Wouldn't Be Alone in Eating Monkeys

If gorillas do eat meat, they wouldn't be the first great apes to do so.

Chimpanzees and their bonobo cousins are known to hunt and eat other mammals, including monkeys. (See "'Loving' Bonobos Seen Killing, Eating Other Primates.")

Plus, "most herbivores can digest meat quite well," said study co-author Michael Hofrieter, a geneticist also at the Max Planck Institute. "It just does not work the other way around."