The knowns and unknowns of chimpanzee culture.

Claims of culture in chimpanzees appeared soon after the launch of the first field studies in africa.1 The notion of chimpanzee 'material cultures' was coined,2 and this was followed by a first formal comparison, which revealed an astonishing degree of behavioural diversity between the different study communities, mainly in terms of tool use.3 Although this behavioural diversity is still undisputed, the question of chimpanzee cultures has remained controversial.4-6 The debate has less to do with the definition of culture (most animal behaviour researchers accept the notion for behaviour that is 'transmitted repeatedly through social or observational learning to become a population-level characteristic' 3), but more with whether some key criteria are met.