Self-Control In Animals Linked To Brain Size; Chimps Have More Inhibitions Than Gerbils [VIDEO]

By Ben Wolford on April 22, 2014 2:12 PM EDT

This squirrel can't help but approach the food inside a transparent cylinder from head on, even though it's been trained to approach from the side. (Photo: Screenshot/YouTube)
This squirrel can't help but approach the food inside a transparent cylinder from head on, even though it's been trained to approach from the side. (Photo: Screenshot/YouTube)

Scientists are always interested in testing animal intelligence because of the clues critters could offer about how humans got so smart. Cognitive evolution is one of the least understood areas of evolutionary biology. In a new study, researchers went all out, testing 36 different species in two problem-solving tasks designed to measure their self-control.

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What they discovered is that bigger brains and diverse diets are predictors of animal smarts, according to the study, published Monday in Proceedings of the National Academy of Sciences. Primates were the brightest (of course). Gerbils and squirrels, not so much.

"The study levels the playing field on the question of animal intelligence," said University of California, Berkeley, psychologist Lucia Jacobs, who co-authored the paper, in a summary of the findings. In a precursory paper published in Animal Cognition in 2012, Jacobs and her colleagues wondered, "Why do some species make tools or learn what to eat from [others in their species] whereas others do not? Why are some species more risk-averse than others when faced with a gamble?"

She contends that testing methodologies developed across the disciplines of evolutionary biology and comparative psychology can answer some of these questions better than researchers have been able to before. Indeed, one unrelated recent study sought to understand what makes some fish more bold than others in foraging for food (ambidextrous brain function was thought to be a cause). In another, scientists wanted to know whether social animals evolved greater intelligence, so they quizzed a group of goats. Their findings suggested goats are smart not because they're social but because they have to overcome difficulties in foraging for food.

The present study was a more massive undertaking, with 58 scientists contributing their own data with their own test subjects. It involved 567 animals from 36 species, which included, according to UC Berkeley: "bonobos, chimpanzees, gorillas, olive baboons, stump-tailed macaques, golden snub-nosed monkeys, brown, red-bellied and aye-aye lemurs, coyotes, dogs, gray wolves, Asian elephants, domestic pigeons, orange-winged amazons, Eurasian jays, western scrub jay, zebra finches, and swamp sparrows."

"Cognition presents evolutionary research with one of its greatest challenges," the authors wrote, adding, "Our results implicate robust evolutionary relationships between dietary breadth, absolute brain volume, and self-control." In other words, those with the biggest brains (not relative to body size) and the least picky eaters were more likely to avoid behavior that was not beneficial.

In one test, all of the animals were trained to find food in a black cylinder by approaching from the open ends. Once they learned how to do it, the black cylinder was replaced with a transparent one. Primates restrained from approaching the food head-on and quickly grabbed the food from the side. The video below shows how it works.

Jacobs and a student were responsible for the rodent data used in the study. The fox squirrels they tested found the food but were initially confused. "About half of the squirrels and gerbils did well and inhibited the direct approach in more than seven out of 10 trials," grad student Mikel Delgado said. "The rest didn't do so well."

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