While robots have been able to play rock-paper-scissors for some time, researchers at Kyoto University and Peking University have now taught the fairly complex skill set associated with the game to chimps. The primates demonstrated an uncanny ability to understand relationships, grasp circular patterns and, according to the researchers, were able to learn and play the game as well as four-year-old humans.

In case you've been living under a rock (see what we did there?), rock-paper-scissors is a game played with the hands. On the count of three, players shoot out their hands in one of three symbols: flat represents paper, a fist represents a rock, and two fingers represent scissors. The game proceeds according to a circular logic pattern: paper covers rock, rock smashes scissors, and scissors cut paper.

In their experiment, the researchers enlisted seven chimpanzees living at the Primate Research Institute at Kyoto University in Japan, all of different ages and representing a mix of sexes. The chimps were each placed in a booth in front of a computer touchscreen and were trained on the relationships between the items. They were shown pairs of items from the game and asked to choose which were more powerful. So in the case of a pair of scissors and a rock, for example, they would learn that the rock was the stronger choice.

The researchers found that five of the animals were able to grasp the game after an average training time of 307 sessions. Of note, however, is the fact that the chimps had trouble with the final pair in the sequence, which was the scissors/paper relationship. This showed that they had a hard time comprehending the circular nature of the pattern, although they did get there eventually.

In addition to training the chimps, the researchers also taught the game to 38 preschool children, aged three to six. They found that children caught on to the game in about five sessions, but that their performance improved as they got older. Under the age of four, the kids' success in the game seemed to rely on luck as much as skill. Starting at four, skill played a greater role. Therefore, the researchers conclude, even though it took the chimps longer to learn the game, their performance once they did appears to be on par with four-year-old humans.

"This suggests that children acquire the ability to learn a circular relationship and to solve a transverse patterning problem around the age of four years," said Jie Gao of Kyoto University in Japan and Peking University in China, who is lead author of the study. Gao is hopeful that his work will spark future studies that delve deeper in the ways in which age and sex play a role in the ability of various species to understand circular relationships.

The research has been published in the journal Primates. It adds to a growing body of knowledge regarding the way in which chimps learn, including a study last year in which the animals were shown actively teaching their young how to use tools.