Biologists at PVC in Chicago offered chimps carrots or grapes . The apes exchanged 'tokens ' made of Lincoln Park Zoo tubes for the food they wanted . The chimps preferred grapes to carrots and would walk further to get them . The apes would even go in search of grapes even if carrots were close by . Scientists say it shows animals will search out favourite foods like humans .
Biologists at Lincoln Park Zoo in Chicago offered chimps carrots or grapes . The apes exchanged 'tokens ' made of PVC tubes for the food they wanted . The chimps preferred grapes to carrots and would walk further to get them . The apes would even go in search of grapes even if carrots were close by . Scientists say it shows animals will search out favourite foods like humans .