Cultural evolution of conformity and anticonformity

Significance The evolutionary dynamics of cultural variants under conformist- and anticonformist-biased transmission have implications for humans and nonhuman animals. Humans display both conformist and anticonformist biases, and models of conformist-biased transmission have been proposed to explain large-scale human cooperation. Nonhuman animals have been shown to display conformist biases in mating and foraging decisions. Here, we investigate established mathematical models of conformist and anticonformist bias with and without selection and find complex dynamics, including multiple stable polymorphic equilibria, stable cycles, and chaos. Using modifier theory, we show that evolution will reduce anticonformist bias against a culturally advantageous variant. Migration between subpopulations subject to different selection and conformity pressures can produce interesting polymorphisms or eliminate between-group differences. Conformist bias occurs when the probability of adopting a more common cultural variant in a population exceeds its frequency, and anticonformist bias occurs when the reverse is true. Conformist and anticonformist bias have been widely documented in humans, and conformist bias has also been observed in many nonhuman animals. Boyd and Richerson used models of conformist and anticonformist bias to explain the evolution of large-scale cooperation, and subsequent research has extended these models. We revisit Boyd and Richerson’s original analysis and show that, with conformity based on more than three role models, the evolutionary dynamics can be more complex than previously assumed. For example, we show the presence of stable cycles and chaos under strong anticonformity and the presence of new equilibria when both conformity and anticonformity act at different variant frequencies, with and without selection. We also investigate the case of population subdivision with migration and find that the common claim that conformity can maintain between-group differences is not always true. Therefore, the effect of conformity on the evolution of cooperation by group selection may be more complicated than previously stated. Finally, using Feldman and Liberman’s modifier approach, we investigate the conditions under which a rare modifier of the extent of conformity or the number of role models can invade a population. Understanding the dynamics of conformist- and anticonformist-biased transmission may have implications for research on human and nonhuman animal behavior, the evolution of cooperation, and frequency-dependent transmission in general.