The scientists started testing other gorillas at their facility. The youngest of the group, a five-year-old named Azizi, is also proving to be a quick study.
So far the male gorilla has only learned to sequence five numbers at a time, but has progressed as rapidly as Rollie.
In Japan similar studies are being conducted with chimpanzees, mandrills, and gibbons. None have made it past the number five.
"This is the first study demonstrating gorilla intelligence like this," said Tetsuro Matsuzawa, director of the Primate Research Institute at Kyoto University.
"I am eager to see how further research with these gorillas progresses."
The discovery raises questions about why gorillas do not use tools more often.
"We are starting to think that gorilla social intolerance blocks innovative behaviors like tool use from spreading widely through a group," said primatologist Elizabeth Lonsdorf, also at Lincoln Park Zoo.
If gorillas gathered together and studied one another—as chimpanzees do—tool use might be a lot more common, Lonsdorf noted.
Another factor could be feeding behavior. Gorillas depend heavily on easily obtained grass and herbs that require no tools for collection, while chimpanzees commonly feed on fruits and nuts which are often hard to access without tools.
"The challenge of obtaining food may be a second reason why chimpanzees invent tools and gorillas do not," Kyoto University's Matsuzawa said.
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