Researchers say, to date, they have found the earliest archaeological examples of monkey tool use outside of Africa. In their paper, published in Current Biology, they suggest it raises questions about the origins and spread of tool use in New World monkeys and, controversially perhaps, prompts us to look at whether early human behaviour was influenced by their observations of monkeys using stones as tools. The research was led by Dr Michael Haslam of the University of Oxford, who in previous papers presents archaeological evidence showing that wild macaques in coastal Thailand used stone tools for decades at least to open shellfish and nuts.
This latest paper involved a team from Oxford and the University of São Paulo in Brazil, who observed groups of modern capuchins at Serra da Capivara National Park in northeast Brazil, and combined this with archaeological data from the same site. Researchers watched wild capuchins use stones as hand-held hammers and anvils to pound open hard foods such as seeds and cashew nuts, with young monkeys learning from older ones how to do the same. The capuchins created what the researchers describe as 'recognisable cashew processing sites', leaving stone tools in piles at specific places like the base of cashew trees or on tree branches after use. They found that capuchins picked their favourite tools from stones lying around, selecting those most suitable for the task. Stones used as anvils were over four times heavier than hammer stones, and hammers four times heavier than average natural stones. The capuchins also chose particular materials, using smooth, hard quartzite stones as hammers, while flat sandstones became anvils.