Chimps can learn rock-paper-scissors (sorta')

Jie Gao, Yanjie SuMasaki Tomonaga, Tetsuro Matsuzawa. Learning the rules of the rock–paper–scissors game: chimpanzees versus children. Primates (2017) https://doi.org/10.1007/s10329-017-0620-0.

Abstract: The present study aimed to investigate whether chimpanzees (Pan troglodytes) could learn a transverse pattern by being trained in the rules of the rock–paper–scissors game in which “paper” beats “rock,” “rock” beats “scissors,” and “scissors” beats “paper.” Additionally, this study compared the learning processes between chimpanzees and children. Seven chimpanzees were tested using a computer-controlled task. They were trained to choose the stronger of two options according to the game rules. The chimpanzees first engaged in the paper–rock sessions until they reached the learning criterion. Subsequently, they engaged in the rock–scissors and scissors–paper sessions, before progressing to sessions with all three pairs mixed. Five of the seven chimpanzees completed training after a mean of 307 sessions, which indicates that they learned the circular pattern. The chimpanzees required more scissors–paper sessions (14.29 ± 6.89), the third learnt pair, than paper–rock (1.71 ± 0.18) and rock–scissors (3.14 ± 0.70) sessions, suggesting they had difficulty finalizing the circularity. The chimpanzees then received generalization tests using new stimuli, which they learned quickly. A similar procedure was performed with children (35–71 months, n = 38) who needed the same number of trials for all three pairs during single-paired sessions. Their accuracy during the mixed-pair sessions improved with age and was better than chance from 50 months of age, which indicates that the ability to solve the transverse patterning problem might develop at around 4 years of age. The present findings show that chimpanzees were able to learn the task but had difficulties with circularity, whereas children learned the task more easily and developed the relevant ability at approximately 4 years of age. Furthermore, the chimpanzees’ performance during the mixed-pair sessions was similar to that of 4-year-old children during the corresponding stage of training.

I took a look at the research paper, and the chimps didn't actually do the manual gestures. They worked at a computer presentation of hand images, choosing the proper one for each move. What the researchers were after was whether or not the chimps could learn transverse patterning (A>B, B>C, C>A), which is fine. But I'd like to know whether or not they could learn the manual gestures and whether or not two chimps could play. I have no intuitions about this, but still, I'd like to know.

The gestures themselves are simple enough, of course. I should think chimps would have no problems But can they manage the interpersonal coordination, the precise synchronization that humans exhibit when playing the game. I'm not so sure chimps could manage that. The experimental set-up doesn't involve the chimps synchronizing with anything.

The game is also known as Rochambeau and had been traced back to early 17th-centrury China. The Wikipedia entry is interesting. Among many other things we learn:

The common side-blotched lizard (Uta stansburiana) exhibits a rock–paper–scissors pattern in its mating strategies. Of its three color types of males, "orange beats blue, blue beats yellow, and yellow beats orange" in competition for females, which is similar to the rules of rock-paper-scissors.