The Evolution of Culture: from Primate Social Learning to Human Culture

The evolution of culture: From primate social learning to human culture Laureano Castro and Miguel A. Toro† Departamento de Mejora Gene´tica Animal, Instituto Nacional de Investigacioń y TecnologıáAgraria y Alimentaria, Carretera de la Corunã Kilo´metro 7, 28040 Madrid, Spain Edited by Francisco J. Ayala, University of California, Irvine, CA, and approved May 20, 2004 (received for review January 8, 2004) Cultural transmission in our species works most of the time as a insufficient to explain the adaptive success of human culture. He cumulative inheritance system allowing members of a group to proved that, as long as the only benefit of imitation is that incorporate behavioral features not only with a positive biological imitators avoid the cost of individual learning, imitation has no value but sometimes also with a neutral, or even negative, bio- effect at all on the evolving organism’s average fitness in the long logical value. Most of models of dual inheritance theory and run. Although imitators do very well when they are rare and gene-culture coevolution suggest that an increase, either qualita- individual learners are common, they do poorly when they are tive or quantitative, in the efficiency of imitation is the key factor common and individual learners are rare. This means that at to explain the transformation of primate social learning in a equilibrium the mean fitness of the population as a whole is the cumulative cultural system of inheritance as it happens during same as that in a population of purely individual learners. hominization. We contend that more efficient imitation is neces- Boyd and Richerson (7) have shown that Roger’s result is sary but not enough for this transformation to occur and that the robust. However, they also show that imitation can be adaptive key factor enabling such a transformation is that some hominids and increase average fitness of imitators if it makes individual developed the capacity to approve or disapprove their offspring’s learning less costly or more accurate. The first condition (i.e., learned behavior. This capacity to approve or disapprove off- imitation makes individual learning less costly) is satisfied if spring’s behavior makes learning both less costly and more accu- individuals use individual learning when it is cheap and reliable rate, and it transformed the hominid culture into a system of and switch to imitation when individual learning is expensive. cumulative cultural inheritance similar to that of humans, although The second condition (i.e., imitation makes individual learning the system was still prelinguistic in nature. more accurate) is satisfied if imitation allows the accumulation of behaviors (i.e., the direct and accurate copying of behaviors) imitation ͉ teaching ͉ assessor ͉ dual inheritance ͉ cultural transmission that no individual learner could acquire by himself from one generation to the next. That is, it allows cumulative cultural ulture defined as variation acquired and maintained by evolution. Cindirect (basically stimulus and local enhancement) and For Boyd and Richerson (7), cumulative cultural evolution is direct (basically imitation) social learning is common in nature, not present in chimpanzees culture because chimpanzees unfold but it reached an important level in Homo sapiens only when it their imitative learning abilities in a less consistent manner than led to a cultural evolution process with a great adaptive value (1, humans do. The authors show that, although cultural accumu- 2). Cultural transmission in our species works most of the time lation is adaptive, the evolution of the psychological capacities as a cumulative inheritance system allowing members of a group that make it possible is difficult when these capacities are rare. to incorporate behavioral features not only with a positive Boyd and Richerson also suggest that it is likely that the cognitive biological value, but sometimes also with a neutral, or even capacities that allow the initial evolution of an efficient capacity negative, biological value. It is not clear how cultural transmis- of imitation must evolve as a side effect of some other adaptive sion has improved human adaptability, especially when other change, e.g., a capacity for theory of mind that may have initially SOCIAL SCIENCES primates with well developed social learning abilities show evolved to allow individuals to better predict the behavior of comparably restricted ranges. Hence, we are left to answer the other members of their social group. Tomasello (8) claims that questions: what types of changes occurred during the homini- the key for the transformation of social learning in hominids into zation process that transformed typical social learning in pri- a human cultural inheritance system was a qualitative change in mates into a cumulative cultural inheritance system similar to imitation ability, which requires as a previous step that individ- that of humans and what was the adaptive advantage that made uals develop a capacity for a theory of mind that would enable these changes possible? The recent developments of the two them to perceive their peers as intentional beings with a similar closely related fields of gene-culture coevolution and dual mind. inheritance theory provided, until now, the most convincing In this paper, we suggest that, in contrast to the common answers to these questions (for reviews, see refs. 3 and 4). assumptions in models of gene-culture coevolution and dual Boyd and Richerson (1) and Cavalli-Sforza and Feldman (5) inheritance theory, imitation in human and nonhuman primates had argued that social learning improves human adaptability by is basically a tool that allows an individual to learn the behaviors exempting individuals from the costs of individual learning that other individuals of the population exhibit but to refrain (basically trial and error learning). Time costs and potential from adopting the behaviors until after further evaluation. From mistakes can make individual learning quite expensive, and this definition of imitation as a process of observational learning therefore, if others individuals have already paid those costs, but not of replication of behaviors without evaluation, we learning from the behavior of these individuals may be cheaper. contend that an increase, either qualitative or quantitative, in the Imitation allows individuals to acquire a vast store of useful efficiency of imitation is not enough to explain the transforma- knowledge without incurring the costs of discovering and testing tion of primate social learning into a cumulative cultural system this knowledge themselves. Rogers (6), using a simple mathematical model, has shown that the fact that social learning (basically imitation) allows an This paper was submitted directly (Track II) to the PNAS office. individual organism to avoid the costs of learning does not †To whom correspondence should be addressed. E-mail: [email protected]. increase the ability of that species of organism to adapt and is © 2004 by The National Academy of Sciences of the USA www.pnas.org͞cgi͞doi͞10.1073͞pnas.0400156101 PNAS ͉ July 6, 2004 ͉ vol. 101 ͉ no. 27 ͉ 10235–10240 Downloaded by guest on September 30, 2021 of inheritance in the strict sense. The key factor enabling such a to reinvent it. Accordingly, the greater the adaptive signifi- transformation was the fact that some hominids developed the cance and the difficulty to develop a given behavior through capacity to approve or disapprove their offspring’s learned individual learning, the greater the selection pressure should behavior. It was this capacity to approve or disapprove off- be in favor of the development of imitation processes, ensuring spring’s behavior that makes learning both less costly and more its rapid acquisition. accurate and that transformed the hominid culture into a system Reader and Laland (12) found empirical evidence that inno- of cumulative cultural inheritance similar to that of humans, vation and social learning frequencies covary across species, a although the system was still prelinguistic in nature. fact that is in conflict with the view that there is an evolutionary tradeoff between reliance on individual learning and imitation as The Evolution of Culture the current models of gene-culture coevolution suggest (see, for Imitation Is Necessary for Human Cultural Transmission but It Is Not example, ref. 3). These findings provide an empirical link Enough. We consider that the adoption of a learned behavior in between behavioral innovation, imitative cognitive capacities, primates can be defined as a process with three steps: (i)to and brain size in mammals. Thus, they imply that the social and discover and to learn a behavior, (ii) to test and to evaluate the ecological intelligence hypotheses for brain evolution must not learned behavior, and (iii) to reject or to incorporate the necessarily be regarded as alternatives and that multiple sources behavior into the behavioral repertory (see ref. 9 for a more of selection favored the evolution of a large primate executive detailed explanation). Primates can discover and learn a behav- brain. Henrich and McElreath (4) suggest that evolution of both ior (the first step) through trial-and-error learning, insight, local individual and social learning (including imitative capacities) has enhancement, imitation, etc., but afterward individuals must test been consequence of an intertwined adaptive response to in- and evaluate learned behavior through their evaluative brain creasing

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