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From an evolutionary perspective, culture can be defined as the part of phenotypic variance that is inherited through social learn-ing.2 When defined in this way, cultural variation becomes part of inclusive heritability2 and is thus open to evolution through natural selection in ways similar to genetic variation. In this context, cultural transmission may thus be viewed as an impor-tant process of evolution. The actual impact of culture, however, may be restricted by a limited prevalence across species with well developed cognitive abilities. Apart from humans, evidence of cultural variation has been reported in a restricted set of mam-mals, such as chimpanzees,5-8 orangutans,9 whales10-12 and some songbirds.13-17 However, the paucity of evidence for cultural variance may result from the lack of methods to identify it. We have recently proposed four testable criteria on which to rely to demonstrate that a trait is at least partially culturally inherited.2,4 The expres-sion of the trait must first result from social learning, which is learning from others18-22 (reviews in refs. 3 and 23–25). This is the essence of culture. Second, variation in the social informa-tion possessed by individuals must be socially transmitted across generations or at least from older to younger individuals.7,26-29 This criterion establishes that the inheritance of behavioral varia-tion across generations results from social learning. Third, social learning must modify the phenotype of the learning individual for sufficient time to allow other individuals to observe and learn its behavior.30-32 The idea is that if a social influence only persists for a short period of time, it may be too labile to be transmit-ted to younger individuals. We only transmit attitudes to whic