Development of stone tool use by wild chimpanzees (Pan troglodytes).

TLDR

Wild chimpanzees at Bossou, Guinea, begin using hammer and anvil stones to crack oil‑palm nuts around age 3.5 years. The study aimed to clarify how stone‑tool use develops in wild chimpanzees by conducting a field experiment that supplied stones and oil‑palm nuts. Researchers observed and video‑recorded three infants (<4 years) from 1992‑95, collecting 692 manipulation episodes and 150 observation episodes to analyze how infants learn stone‑nut cracking. Infants progressed from single actions on a single object to multiple actions on multiple objects, yet by 2.5 years they possessed basic actions but had not yet combined them into a correct nut‑cracking sequence.

Abstract

At the age of 3.5 years, wild chimpanzees at Bossou, Guinea, begin to use hammer and anvil stones to crack oil-palm nuts to get the kernels. To clarify the developmental processes, the authors did a field experiment in which stones and oil-palm nuts were provided. Infant chimpanzees' stone-nut manipulation was observed and video recorded. Data were collected from 3 infants younger than 4 years old from 1992 to 1995. The authors analyzed 692 episodes of infants' stone-nut manipulation and 150 episodes of infants' observation of nut cracking performed by adults. Infants observed other chimpanzees' nut cracking and got the kernels from them. The stone-nut manipulation developed from a single action on a single object to multiple actions on multiple objects. Although infant chimpanzees at the age of 2.5 years already acquired basic actions necessary for nut cracking, they did not combine the actions in an appropriate sequence to perform actual nut cracking.