Our knack for language helps us structure our thinking. Yet the ability to wax poetic about trinkets, tools or traits may not be necessary to think about them abstractly, as was once suspected. A growing body of evidence suggests nonhuman animals can group living and inanimate things based on less than obvious shared traits, raising questions about how creatures accomplish this task.

In a study published last fall in the journal PeerJ, for example, Oakland University psychology researcher Jennifer Vonk investigated how well four orangutans and a western lowland gorilla from the Toronto Zoo could pair photographs of animals from the same biological groups.

Vonk presented the apes with a touch-screen computer and got them to tap an image of an animal—for instance, a snake—on the screen. Then she showed each ape two side-by-side animal pictures: one from the same category as the animal in the original image and one from another—for example, images of a different reptile and a bird. When they correctly matched animal pairs, they received a treat such as nuts or dried fruit. When they got it wrong, they saw a black screen before beginning the next trial. After hundreds of such trials, Vonk found that all five apes could categorize other animals better than expected by chance (although some individuals were better at it than others). The researchers were impressed that the apes could learn to classify mammals of vastly different visual characteristics together—such as turtles and snakes—suggesting the apes had developed concepts for reptiles and other categories of animals based on something other than shared physical traits.

Dogs, too, seem to have better than expected abstract-thinking abilities. They can reliably recognize pictures of other dogs, regardless of breed, as a study in the July 2013 Animal Cognition showed. The results surprised scientists not only because dog breeds vary so widely in appearance but also because it had been unclear whether dogs could routinely identify fellow canines without the advantage of smell and other senses. Other studies have found feats of categorization by chimpanzees, bears and pigeons, adding up to a spate of recent research that suggests the ability to sort things abstractly is far more widespread than previously thought.

There is still some question as to whether such visual categorization experiments reflect truly abstract thinking by animals, says Vonk, who noted that further work is needed to untangle the tricks various animals use in classification challenges. “I suspect the different species use different means of solving the task,” she notes.