The evolution of animal 'cultures' and social intelligence

Abstract

Decades-long field research has flowered into integrative studies that, together with experimental evidence for the requisite social learning capacities, have indicated a reliance on multiple traditions ('cultures') in a small number of species. It is increasingly evident that there is great variation in manifestations of social learning, tradition and culture among species, offering much scope for evolutionary analysis. Social learning has been identified in a range of vertebrate and invertebrate species, yet sustained traditions appear rarer, and the multiple traditions we call cultures are rarer still. Here, we examine relationships between this variation and both social intelligence--sophisticated information processing adapted to the social domain--and encephalization. First, we consider whether culture offers one particular confirmation of the social ('Machiavellian') intelligence hypothesis that certain kinds of social life (here, culture) select for intelligence: 'you need to be smart to sustain culture'. Phylogenetic comparisons, particularly focusing on our own study animals, the great apes, support this, but we also highlight some paradoxes in a broader taxonomic survey. Second, we use intraspecific variation to address the converse hypothesis that 'culture makes you smart', concluding that recent evidence for both chimpanzees and orangutans support this proposition.

Figure 1

Social learning and encephalization in primates. Frequency of social learning in the survey of Reader & Laland (2002) is plotted against executive brain ratio (see text for further explanation). Labels added here refer to three species with complex cultures discussed extensively in the text.

Figure 2

Relationship between association time and number of cultural variants across populations of orang-utans or chimpanzees, for (a) cognitively simple and (b) cognitively complex variants. For (a), analysis of covariance reveals no significant effects of association or species, nor of their interaction; for (b) all these effects are significant (association, p=0.003; species, p=0.01; interaction, p=0.02). Data on cultural variants are from Whiten et al. (1999) for chimpanzees, and van Schaik et al. (2003a) for orang-utans; see text and endnote 4 for assignment of cognitive complexity of variants. Animals were ‘in association’ when they had one or more independent conspecifics at less than 40 or 50 m (variable between studies); data from Boesch (1996) for chimpanzees and van Schaik et al. (2003a) for orang-utans.

Figure 3

The propensity to use tree-hole tools in two clusters of (sub)adult orang-utan females at Suaq Balimbing that vary in mean party size (including only independent individuals in association with focal females; hence, minimum party size is 1). Numbers in parentheses indicate the number of females; vertical bars are standard deviations. Results of t-tests for tool use rate: p<0.05; for party size: p<0.01. Party size differences among females remained constant over time, including following maturation. Data from van Schaik et al. (2003b).

Figure 4

Culture pyramid. Social information transfer (foundation layer) is widespread in vertebrates and occurs also in invertebrates (see text for references). However, only a subset of such transfer eventuates in sustained traditions (layer two), because effects of social learning are often transitory only (e.g. using public information to judge profitable foraging patches). The occurrence of traditions may also be more restricted taxonomically than use of social information per se. More rarely still, cultures exist that are defined by the existence in the same species of multiple traditions forming unique local complexes (layer three). Cumulative culture (layer 4) occurs when more complex traditions arise by elaboration on earlier ones, generating the richness of human cultures yet minimally evidenced in other species. Relative sizes of each layer are notional. Arrows indicate the reliance of each layer on pre-existing lower layers.