Inferring individual-level processes from population-level patterns in cultural evolution

Abstract

Our species is characterized by a great degree of cultural variation, both within and between populations. Understanding how group-level patterns of culture emerge from individual-level behaviour is a long-standing question in the biological and social sciences. We develop a simulation model capturing demographic and cultural dynamics relevant to human cultural evolution, focusing on the interface between population-level patterns and individual-level processes. The model tracks the distribution of variants of cultural traits across individuals in a population over time, conditioned on different pathways for the transmission of information between individuals. From these data, we obtain theoretical expectations for a range of statistics commonly used to capture population-level characteristics (e.g. the degree of cultural diversity). Consistent with previous theoretical work, our results show that the patterns observed at the level of groups are rooted in the interplay between the transmission pathways and the age structure of the population. We also explore whether, and under what conditions, the different pathways can be distinguished based on their group-level signatures, in an effort to establish theoretical limits to inference. Our results show that the temporal dynamic of cultural change over time retains a stronger signature than the cultural composition of the population at a specific point in time. Overall, the results suggest a shift in focus from identifying the one individual-level process that likely produced the observed data to excluding those that likely did not. We conclude by discussing the implications for empirical studies of human cultural evolution.

Analysing Cultural Frequency Data: Neutral Theory and Beyond

“…Similarly, recent work in cultural evolution has pointed to the importance of analysing temporal patterns of change as opposed to static measures of cultural diversity [e.g. 38,43,45,59,85]. For example, Sindi and Dale [85] analysed the patterns of frequency change, in particular, the kurtosis of the distribution of changes over time, of stable words in the Google Ngram database.…”

“…More generally random drift and innovation are not exclusive to neutral theory and hence expected differences in population-level patterns are rooted in the specifics of the underlying cultural transmission process. Kandler et al [45] started examining this problem theoretically by developing a simulation framework aimed at exploring the level of distinguishability of processes of cultural transmission from population-level statistics. To do so they generated the probability distributions for a number of statistics such as the level of cultural diversity conditioned on different transmission processes.…”

Cultural linkage: the influence of package transmission on cultural dynamics

“…Next, we explore the possibility of rejecting unbiased transmission as the probable underlying transmission process if we falsely assumed no links between cultural traits. Following [27], we ran 1000 simulations for certain parameters and calculated areas of overlap between the distributions of final pairwise differences π 1 under unbiased linked transmissions with a = 0.01, b = 0.1 and unbiased unlinked transmission with a = 0 as well as the standard Wright-Fisher model. The areas of overlap represent a general measure of equifinality.…”

Creativity: linchpin in the quest for a viable theory of cultural evolution

“…While transmission-the spread of existing traits-is a component of evolution, evolution additionally entails cumulative, adaptive, open-ended change. Studies that do incorporate cultural novelty are often limited to trivial sources such as 'cultural mutation' [65] or copying error [66], thereby neatly avoiding the issue of creativity.…”