7 min read

Great Apes Are Masters At Detecting Deception

Nobody likes to be deceived - especially when there's food involved. And most great apes, as well as two-and-a-half-year-old kids, can tell when someone is trying to fake them out of a bigger pretzel stick, a team of German primatologists have discovered.

It's the first time orangutans, bonobos and gorillas have been shown to discriminate between appearance and reality, says study author Katja Karg, a primate expert at Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, in an email to The Dodo. Karg and her colleagues also confirmed the results of a previous study showing that chimpanzees are no slouches at seeing through a false appearance, either.

Using sticks of food, the researchers set up a series of tests designed to measure the ability of an ape to discriminate reality from illusion. The goal of each test was simple: Pick the biggest stick. But what looked like the longest stick wasn't always actually the biggest - the scientists used a sliding board to alter the sticks' appearances, similar to the way a carton obscures all but the tips of french fries. During the tests, the board made a long stick seem small and the small stick seem long. (It showed 0.8 inches of a 5-inch pretzel but 1.6 inches of a 2.5-inch stick.)

In the "reality view," (left) pretzels are shown as they actually are; in the false "appearance view" (right), an ape sees only the ends of the food sticks. (Photo: Karg et al.)

A bonobo named Yasa successfully picks the larger food stick.

The researchers were able to rely on the fact that non-human apes have a natural preference for bigger pieces of food. "Great apes have a very strong tendency to choose the larger food of two pieces," Karg says. Chimpanzees, gorillas, bonobos and orangutans would readily snag what they perceived to be larger pretzels. (The primatologists taught the little humans to pick fake "food sticks" with the aid of a sock puppet: "Children generally reacted positively to the [puppet] and seemed to enjoy feeding it," the researchers wrote.)

If just the tips of the pretzels were showing, each primate species frequently chose the deceptively large stick. But when apes and kids watched as the board was slid in place (or if it started in place, was removed, then returned), they were more likely to see through the illusion and point to the actually longer object.

Carla Krachun, a primate expert at Memorial University of Newfoundland, Canada, who was not involved in the study, and her colleagues had previously shown that chimpanzees could overcome an optical illusion of small grapes looking bigger due to magnifying lenses. "It's extremely interesting that they found similar performances across all species," she says in an email to The Dodo.

Apes that see through deception have a leg up, evolutionarily speaking - the natural world is full of things that aren't what they appear. "Camouflage and mimicry are obvious examples," Krachun says, or "objects appear bigger when immersed in water, or appear a different color under different lighting conditions." And mistaking a snake for a branch, for example, could have lethal consequences.

Krachun believes studies like these could help shed light on the way reality and appearance clash in the social world, too. "Other individuals may misrepresent their feelings, intentions, abilities, identity," she says. "And knowing this would allow one to avoid being misled by others, and also to mislead others to one's own advantage."

Anecdotally, there's evidence great apes have tried to visually deceive each other. A chimp might try to bluff about his size by puffing up his hair, Karg points out. And in one instance, a chimp covered "his erect penis with his hands so that a dominant competitor could not see it (this saved him from an aggressive interaction)."

Great ape subterfuge goes beyond bristling chimpanzee fur, of course. "Humans are a very deceptive species - we smile even if we do not mean it, we lie, we betray," Karg says. "In the human world it is thus for sure an advantage if you know what is real and what is fake, so that you can base your decisions on reality."