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Mon­keys in Brazil ‘have used stone tools for hun­dreds of years at least’

pub­lished 13 July 2016 | mod­i­fied 13 July 2016

New archae­o­log­i­cal evi­dence sug­gests that Brazil­ian capuchins have been using stone tools to crack open cashew nuts for at least 700 years, and the new research paper asks whether human behav­iour was influ­enced through watch­ing the monkeys.

Capuchin use stone tool to crack cashew nutResearchers say, to date, they have found the ear­li­est archae­o­log­i­cal exam­ples of mon­key tool use out­side of Africa. In their paper, pub­lished on 11 July 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.

Using archae­o­log­i­cal meth­ods, the researchers exca­vated a total of 69 stones to see if this tool tech­nol­ogy had devel­oped at all over time. They dug to a depth of 0.7 metres at a site close to cashew trees where they had seen mod­ern capuchins fre­quently using their stone tools. They iden­ti­fied the tools from inspect­ing the size and shape of the stones, as well as the dis­tinc­tive dam­age on the stone sur­face caused by capuchin pound­ing. Through mass spec­trom­e­try, the researchers were able to con­firm that dark-​coloured residues on the tools were specif­i­cally from cashew nuts. They also car­bon dated small pieces of char­coal dis­cov­ered with the stones to estab­lish the old­est were least 600 to 700 years old — mean­ing the tools pre­date the arrival of Euro­peans in the New World.

Mon­keys have used stone tools for hun­dreds of years:

(Source: Uni­ver­sity of Oxford YouTube chan­nel; credit Michael Haslam, Uni­ver­sity of Oxford)

In the paper, the researchers esti­mate that around 100 gen­er­a­tions of capuchins have used this tra­di­tion of stone tools. They com­pared tools used by mod­ern capuchins with the old­est exca­vated exam­ples, find­ing they are sim­i­lar in terms of weight and mate­ri­als cho­sen. This appar­ent lack of change over hun­dreds of years sug­gests mon­keys are ‘con­ser­v­a­tive’, pre­fer­ring not to change the tech­nol­ogy used, unlike humans liv­ing in the same region, says the paper.

This is an excit­ing, unex­plored area of sci­en­tific study that may even tell us about the pos­si­ble influ­ence of mon­keys’ tool use on human behaviour.
Dr Michael Haslam, lead author, School of Archae­ol­ogy, Uni­ver­sity of Oxford, UK »

Dr Michael Haslam said: ‘Until now, the only archae­o­log­i­cal record of pre-​modern, non-​human ani­mal tool use comes from a study of three chim­panzee sites in Cote d’Ivoire in Africa, where tools were dated to between 4,300 and 1,300 years old. Here, we have new evi­dence that sug­gests mon­keys and other pri­mates out of Africa were also using tools for hun­dreds, pos­si­bly thou­sands of years. This is an excit­ing, unex­plored area of sci­en­tific study that may even tell us about the pos­si­ble influ­ence of mon­keys’ tool use on human behav­iour. For exam­ple, cashew nuts are native to this area of Brazil, and it is pos­si­ble that the first humans to arrive here learned about this unknown food through watch­ing the mon­keys and their pri­mate cashew-​processing industry.’

Tool use by mon­keys has fea­tured in other research led by Dr Haslam in recently pub­lished papers. In a study in the Jour­nal of Human Evo­lu­tion (pub­lished in June 2016), the team noted how groups of macaques in the marine national park on Piak Nam Yai Island, Thai­land, selected stones as tools to crush marine snails, nuts and crabs. They also iden­ti­fied 10 tools in exca­va­tions at the site, which they dated as between 10 and 50 years old. In another research paper detail­ing field­work at the same site, they say the mod­ern macaques typ­i­cally moved their tools a metre or less from where they picked them up, but the longest dis­tance they observed was around 87m. The macaques ate nine oys­ters at a time, on aver­age, and gen­er­ally car­ried the same tool over short dis­tances. In one case, how­ever, the researchers saw a hun­gry macaque eat 63 oys­ters one after the other, using the same stone tool to open all the shells, says the paper.

More infor­ma­tion on an evo­lu­tion­ary con­text for the emer­gence of tech­nol­ogy and its use by pri­mates, includ­ing our own ances­tors, is avail­able as a result of the Pri­mate Archae­ol­ogy project.

(Source: Uni­ver­sity of Oxford news release, 12.06.2016)

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