Do Sigmoidal Acquisition Curves Indicate Conformity?

Abstract

The potential for behaviours to spread via cultural transmission has profound implications for our understanding of social dynamics and evolution. Several studies have provided empirical evidence that local traditions can be maintained in animal populations via conformist learning (i.e. copying the majority). A conformist bias can be characterized by a sigmoidal relationship between a behavior's prevalence in the population and an individual's propensity to adopt that behavior. For this reason, the presence of conformist learning in a population is often inferred from a sigmoidal acquisition curve in which the overall rate of adoption for the behavior is taken as the dependent variable. However, the validity of sigmoidal acquisition curves as evidence for conformist learning has recently been challenged by models suggesting that such curves can arise via alternative learning rules that do not involve conformity. We review these models, and find that the proposed alternative learning mechanisms either rely on faulty or unrealistic assumptions, or apply only in very specific cases. We therefore recommend that sigmoidal acquisition curves continue to be taken as evidence for conformist learning. Our paper also highlights the importance of understanding the generative processes of a model, rather than only focusing solely on the patterns produced. By studying these processes, our analysis suggests that current practices by empiricists have provided robust evidence for conformist transmission in both humans and non-human animals.

Increased initial task difficulty drives social foragers to develop sub-optimal conformity instead of adaptive diversity

“…In the broad sense that will be used in this paper (and as commonly used in spoken language), conformity, or the tendency to conform, refers simply to 'copying the most common behaviour' regardless of the exact mechanism leading to it. Narrower definitions of conformity have included a tendency to copy the majority (or the common behaviour) with a probability that is greater than its current proportion [31][32][33], or a tendency to change existing behaviour to match a majority [24,25,29]. These extra conditions are clearly of interest, but require quantification of the learning process in a way that is not always possible.…”

Strong conformity requires a greater proportion of asocial learning and achieves lower fitness than a payoff-based equivalent

“…The simulations of Acerbi and colleagues (Acerbi & van Leeuwen, 2017; Acerbi et al, 2016) demonstrate that preference for one cultural trait over another or social learning from small subsets of the population can lead to results indistinguishable from those expected under conformist social learning. Although these alternative generating processes may be realistic only under a limited set of conditions (Smaldino, Aplin, & Farine, 2017), they raise a substantive equifinality problem that deserves greater attention (Barrett, 2018).…”

Movement and conformity interact to establish local behavioural traditions in animal populations

“…These conformist learning functions produce a sigmoidal relationship between a solution’s prevalence in the sub-population and the probability of adoption of that behavioural preference (called acquisition curve; [26,27]; S1 Fig). The conformity parameter λ determines the strength of sigmoidality (i.e.…”