On the nature of cultural transmission networks: evidence from Fijian villages for adaptive learning biases

Abstract

Unlike other animals, humans are heavily dependent on cumulative bodies of culturally learned information. Selective processes operating on this socially learned information can produce complex, functionally integrated, behavioural repertoires-cultural adaptations. To understand such non-genetic adaptations, evolutionary theorists propose that (i) natural selection has favoured the emergence of psychological biases for learning from those individuals most likely to possess adaptive information, and (ii) when these psychological learning biases operate in populations, over generations, they can generate cultural adaptations. Many laboratory experiments now provide evidence for these psychological biases. Here, we bridge from the laboratory to the field by examining if and how these biases emerge in a small-scale society. Data from three cultural domains-fishing, growing yams and using medicinal plants-show that Fijian villagers (ages 10 and up) are biased to learn from others perceived as more successful/knowledgeable, both within and across domains (prestige effects). We also find biases for sex and age, as well as proximity effects. These selective and centralized oblique transmission networks set up the conditions for adaptive cultural evolution.

Figure 1.

Inferred cultural transmission networks for our three domains. The top row shows the networks for the villages of Teci and Dalomo while the bottom row shows Bukama. Each column represents one of the three domains. Nodes represent individuals. The lines and arrows point towards the selected model. Node sizes are proportional to the number of individuals who selected that person as a model. Node shapes and colours mark individuals' villages and sexes. Blue, males; red, females.

Figure 2.

Effect sizes and confidence intervals for our primary predictor variables in odds ratios. The inset plot is the same as the larger plot except that the axis is rescaled so the smaller odds ratios can be seen. The bars give the odds ratios for our estimated coefficients. Odds ratios greater than 1 indicate positive effects while those less than 1 indicate negative effects. The error bars are 95% CI estimated by resampling. The bar colours mark the different cultural domains. Green, Medicinal Plants odds ratio; red, Yams odds ratio; blue, Fishing odds ratio.