Scientists from Brazil and Germany conducted a study that revealed that for capuchins using tools, social signals play a more significant role than the physical characteristics of the material itself.
As part of the experiment, researchers provided the monkeys with stones intended for cracking nuts, while changing two parameters: the hardness of the stones and the presence of traces of previous use on them.
It was observed that when the tools lacked any signs of use, the capuchins made their choice based on the stone's hardness. However, as soon as traces of use appeared on the tools, the factor of hardness ceased to play a decisive role in decision-making.
Despite the change in selection criteria, this study established that the way the monkeys chose tools had no effect on the ultimate success of the nut-cracking process. The results of the work were published in the journal Proceedings of the Royal Society B.