How to beat a chimpanzee at rock, paper, scissors

By Sarah Knapton

It's late. You're alone and hungry in the jungle with only a chimpanzee, one banana and your wits to get you through the night.

But, fear not, scientists have found the perfect parlour game to play with a primate to win your dinner: rock, paper scissors.

Japanese primatologists have proven that chimps understand and can play the game. However they have a fatal Achilles' heel. The apes take far longer to grasp that scissors can beat paper, than to understand the other winning combinations.

So selecting paper should ensure the banana is safe, even if the chimp demands a rematch.

Previously scientists have found that chimpanzees can make tools, have distinct personalities and even communicate through a rudimentary language of sounds and gestures.

But it is the first time they have shown that they are as capable of grasping the complex patterns to comprehend a game like rock, paper, scissors, which takes enhanced mental capacity.

In fact, they have the same mental agility as a four year old child, scientists have concluded.

Lead author Jie Gao, of the Primate Research Institute at Kyoto University in Japan, said: "The present study aimed to investigate whether chimpanzees could learn a transverse pattern by being trained in the rules of the 'rock, paper, scissors' game.

"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."

In the popular game the hand signal for 'paper' always beats 'rock', while 'rock' trumps 'scissors', and 'scissors' defeats 'paper'.

Seven chimpanzees of different ages and sexes living in Kyoto University's Primate Research Institute took part in the experiment.

They sat in a booth housing a computer-based touchscreen and were trained to choose the winning hand signal when they saw it on screen. When the chimpanzees made the correct choice in a trial, a piece of apple was provided via a feeder in conjunction with a chime sound.

When the wrong stimulus was chosen, an error buzzer sounded, and no food was provided. The food reward was delivered through a feeder to a food tray placed at the bottom of the display.

The findings show that chimpanzees can learn the circular pattern at the heart of the game.

However, it took them an average of 14 sessions to learn the third scissors-paper pair than it did the others, which they picked up in between one and three sessions.

The team then also taught the game to 38 preschool children to compare the learning process of chimpanzees with that of humans aged three to six.

The children had little difficulty grasping the game, and on average did so within five sessions. Researchers say their ability is similar to that of a four year old human child.

The research was published in Primates, the official journal of the Japan Monkey Centre.