A new study suggests mammalian carnivores with larger brains relative to body size are better problem solvers. The findings, published in the journal PNAS, support the controversial theory that relative brain size is a sufficient predictor of intelligence.

A team of zoologists administered a problem solving test to 140 animals from nine different zoos and encompassing 39 different mammalian carnivore species. The test-takers included polar bears, arctic foxes, tigers, river otters, wolves and spotted hyenas, as well as bearcats, snow leopards and wolverines.

Each animal was given 30 minutes to extract food from a metal box by sliding a bolt latch that released the door. Inside the box was each animal's favorite food -- bamboo for pandas, steak for tigers and snow leopards, and so on.

The species with larger brains relative to their body size were the most successful at opening the box and accessing their edible prize.

"This study offers a rare look at problem solving in carnivores, and the results provide important support for the claim that brain size reflects an animal's problem-solving abilities -- and enhance our understanding of why larger brains evolved in some species," lead study author Sarah Benson-Amram, an assistant professor of zoology and physiology at the University of Wyoming, said in a press release.

"Overall, 35 percent of animals, 49 individuals from 23 species, were successful in solving the problem," explained study co-author Ben Dantzer, an assistant professor at the University of Michigan. "The bears were the most successful, solving the problem almost 70 percent of the time. Meerkats and mongooses were the least successful, with no individuals from their species solving the problem."

Larger animals were generally poorer problem solvers than smaller animals, but researchers found dexterity did not predict an animal's success.

Scientists accounted for potentially mitigating factors, but failed to find alternative explanations for the success of species with larger brains relative to body size.

They also failed to find evidence of what scientists call the the "social brain hypothesis," which suggests highly social animals evolved larger brains to handle their increasingly complex living situations.

"This hypothesis posits that intelligence evolved to enable animals to anticipate, respond to and, perhaps, even manipulate the actions of others in their social groups," explained Kay Holekamp, a co-author and distinguished professor at Michigan State University.

"If the social brain hypothesis is correct, then we would expect that species that live in larger social groups would be more intelligent," Holekamp said. "However, we did not find any support for the social brain hypothesis in this study. There was no indication that social group size influenced problem-solving abilities."