At the "stone-leaf-scissors" game, chimpanzees reach the level of a four-year-old child, report Japanese researchers who have subjected to the same training of human and simian primates. Our cousins would struggle with the circular logic ...

Researchers at the University of Kyoto, Japan, have taught chimpanzees the game of chifumi, aka "stone-leaf-scissors", among other appellations. Of the seven primates of the experiment, five reached the end of this training in front of a computer screen, with a treat at each victory. The game took place with pairs: in front of each object presented, the animal had the choice between two possibilities.
The training began with a single pair, in this case leaf-stone. The chimpanzees then discovered the stone-scissors pair and then the scissors-leaf pair. This chifumi course ended in the most difficult phase, with the three pairs mixed. With an average of 307 games, the five primates have completed their apprenticeship.

The chifumi is not so simple for a chimpanzee

It took much more time (about 14 games) to understand that the scissors beat the sheet (yet the last pair studied), compared to the stone-scissors (assimilated after three strokes) and leaf (1.7 strokes on average). According to the researchers, chimpanzees have trouble with the circular character of reasoning: the leaf beats the stone, the stone beats the scissors but the scissors beat the leaf.