Experimentally induced innovations lead to persistent culture via conformity in wild birds

Abstract

In human societies, cultural norms arise when behaviours are transmitted with high-fidelity social learning through social networks1. However a paucity of experimental studies has meant that there is no comparable understanding of the process by which socially transmitted behaviours may spread and persist in animal populations2,3. Here, we introduce alternative novel foraging techniques into replicated wild sub-populations of great tits (Parus major), and employ automated tracking to map the diffusion, establishment and long-term persistence of seeded behaviours. We further use social network analysis to examine social factors influencing diffusion dynamics. From just two trained birds in each sub-population, information spread rapidly through social network ties to reach an average of 75% of individuals, with 508 knowledgeable individuals performing 58,975 solutions. Sub-populations were heavily biased towards the technique originally introduced, resulting in established local arbitrary traditions that were stable over two generations, despite high population turnover. Finally, we demonstrate a strong effect of social conformity, with individuals disproportionately adopting the most frequent local variant when first learning, but then also continuing to favour social over personal information by matching their technique to the majority variant. Cultural conformity is thought to be a key factor in the evolution of complex culture in humans4-7. In providing the first experimental demonstration of conformity in a wild non-primate, and of cultural norms in foraging techniques in any wild animal, our results suggest a much wider evolutionary occurrence of such apparently complex cultural behaviour.

A reappreciation of ‘conformity’

“…starting from a random mixture of the two behaviours, but it clearly shows that different analysis may lead to different results. More specifically, in this case, the analysis based on individuals reveals perfect linearity, in keeping with the individual level random copying default, whereas the analysis based on behaviours reveals the sigmoidal relation between copying probability and relative frequency characteristic of conformist transmission (see Aplin et al, 2015b). In other words, the analysis based on behaviours leads to a detection of conformist transmission where clearly there is none (because all copying here is random).…”

“…Specifically, we note that the gold standard to evidence conformist transmission has been to identify a sigmoidal relation between individuals' probability of copying the majority and the proportional majority size (e.g. see Aplin et al, 2015b;Battesti et al, 2015;Boyd & Richerson, 1985;Chou & Richerson, 1992;Claidiere, Bowler, & Whiten, 2012; but see Acerbi, van Leeuwen, Haun, & Tennie, 2016). A simple agent-based model may help illustrate one of the problems arising from considering the frequencies of behaviours, instead of the frequencies of individuals, in detecting this sigmoidal signature of conformist transmission.…”

“…'conformist transmission'. Aplin et al (2015a) based their argument on the fact that in their original great tit study (Aplin et al, 2015b), the birds did not seem to distinguish between individuals and behaviours (analysed in Aplin et al, 2015a). Following up on this debate, Whiten & van de Waal, (this issue) echo Aplin et al's position by showing that in their vervet monkey study (van de Waal et al, 2013) the frequency of individuals using a certain behavioural option and the frequency of demonstration of this particular behavioural option in total did not affect the observers differently.…”

“…Therefore, the reported correlation between the frequency of individuals and behaviours, while representing an affirmation of internal validity, has no power to falsify alternative hypotheses. For instance, Aplin et al (2015b), although confronted with similar limitations, owing to working with wild animal populations, obtained detailed records of birds responding to differently sized majorities and incorporated their majority numbers, in terms of individuals and behaviours, into statistical analyses to provide insight into whether the birds actually used the majority cue or merely obtained the most common strategy randomly. Without such analysis, our understanding of transmission biases is not furthered by the reporting of a correlation between two possible measures.…”

Cultural Evolution: A Review of Theory, Findings and Controversies

“…showed that nine-spined sticklebacks abandoned a food patch they had previously learned was optimal when they observed a demonstrator feeding at a higher-payoff patch. Conformity has been demonstrated in stickleback and great tits (Aplin et al 2014), with an individual fish or bird disproportionately more likely to feed at a location where a majority of other individuals had fed. These studies with phylogenetically diverse species show that adaptive social learning rules likely evolved independently in response to particular ecological conditions rather than exclusively in our own species' recent ancestors.…”