Chimps Play Rock-Paper-Scissors Like a Four-Year-Old Human

Soon, chimpanzees may have a way to decide who gets the last banana.

Japanese researchers have taught chimpanzees the rules for rock-paper-scissors, and the great apes can play the game at the level of a four-year-old human. The results were published in a study published last week in the journal Primates.

Seven chimps of various ages were shown symbols for each play on a computer touch screen at the Primate Research Institute at Kyoto University. For the first round of training, the monkeys had to pick the winning move between paper and rock. If they correctly picked the hand signal for paper, they heard a chime and received a piece of apple. If they incorrectly picked rock, they did not receive the prize. Once they could guess correctly 90% of the time, the chimps were then trained only on rock versus scissors, and finally on paper versus scissors.

Chimpanzees were demonstrated a grasp of circular patterns in performing rock-paper-scissors tasks.

The chimps did relatively well with the paper-rock and rock-scissors combinations, learning the skills after an average of about two sessions and three sessions, respectively. But they struggled with paper-scissors, and it took them about 14 sessions to learn this rule.

Then they had to show off what they had learned: they were shown a random assortment of all three pairs, and had to pick the correct move. After an average of 307 sessions, five out of the seven chimps could pick the winning signal at least 90% of the time. One stellar chimp, Ayumu, learned all the rules after only 161 sessions. The remaining two monkeys did perform the task, but were not able to reach the 90% threshold.

To assess the complexity of paper-rock-scissors, they compared the chimps’ performance with 38 children between the ages of three to six. The children were trained in a similar manner, but when they responded correctly, they heard a chime and were rewarded with a picture of infant chimpanzees playing. They progressed to the next pair if they could identify four consecutive correct answers. The kids learned the paper versus rock rule in about seven sessions, the rock versus scissors rule in six sessions, and the scissors versus paper rule in five sessions. Children over the age of four performed the task more quickly and accurately than those younger than four.

Here’s Harry Cockburn, interviewing lead author Jie Gao for the Independent:

“The chimpanzees’ performance was similar to that of four-year-old children. The primary difference between the chimpanzees and children in the present study was the method of learning.

“Children changed their choice immediately after they made a wrong one, whereas the chimpanzees would often take multiple sessions to correct themselves.”

The chimps had difficulty understanding the cyclic pattern in which papers beat rock, rock beats scissors, and scissors beats paper (this last one was particularly challenging). But the children found each of these pairs equally easy to learn. How chimps learned in this study is similar how rats and pigeons have been observed in other studies, the authors write.

Deciphering how chimps learn may help us understand how they solve complex problems and form social networks. Next, the researchers want to know if chimps can play the game with each other by applying the same logic. And one day, they may even pit kids versus apes to see who wins.