Social cues on stone tools outweigh raw material properties in wild primates

1.The ability to select appropriate tool material enabled early hominins access to new resources and environments. The underlying mechanisms driving tool selection effectively remain unknown. Observations of extant primates have demonstrated strong selectivity for specific tools, offering analogous insight into technological decision-making. However, whether tool selection is determined by individual experience alone or social information plays a role remained difficult to disentangle. Here, we used an experimental approach to investigate decision-making factors for tool selection in non-human primates. We provided naturalistic nut-cracking opportunities to wild capuchin monkeys, one of the most prolific extant tool users. We offered standardized stones varying in asocial (material properties) and social cues (evidence of previous use) to two populations, differing in their previous experience of natural materials. Our results show that both populations persistently selected tools based on their material properties when only asocial cues were provided. However, when provided with both asocial and social cues combined, they consistently selected previously used material regardless of material properties. These findings suggest that wild capuchin monkeys discriminate between raw material properties; however, prioritize social cues when present. Tool selection behaviors are therefore shaped by indirect social processes and highlight the importance of culturally transmitted information for skill acquisition in technological primates.