On randomly changing conformity bias in cultural transmission

Denton, Kaleda K.; Liberman, Uri; Feldman, Marcus W.

doi:10.1073/pnas.2107204118

“…The difficulty for social learning to increase in frequency may pose a barrier to the evolution of cumulative culture. However, there is increasingly strong evidence that some species can learn socially: social learning has been widely observed in species of primates, birds, fishes, cetaceans and insects [64], and conformity [12,16,65] or a combination of conformity and anti-conformity [17] (discussed in [66], p. 10) has also been documented in non-human animals. We now turn to the question of why a population of social learners might not accumulate culture.…”

Section: Discussionmentioning

confidence: 99%

Conditions that favour cumulative cultural evolution

Denton

¹

,

Ram

²

,

Feldman

³

2023

Phil. Trans. R. Soc. B

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The emergence of human societies with complex language and cumulative culture is considered a major evolutionary transition. Why such a high degree of cumulative culture is unique to humans is perplexing given the potential fitness advantages of cultural accumulation. Here, Boyd & Richerson’s (1996 Why culture is common, but cultural evolution is rare. Proc. Br. Acad. 88 , 77–93) discrete-cultural-trait model is extended to incorporate arbitrarily strong selection; conformist, anti-conformist and unbiased frequency-dependent transmission; random and periodic environmental variation; finite population size; and multiple ‘skill levels.’ From their infinite-population-size model with success bias and a single skill level, Boyd and Richerson concluded that social learning is favoured over individual learning under a wider range of conditions when social learning is initially common than initially rare. We find that this holds only if the number n of individuals observed by a social learner is sufficiently small, but with a finite population and/or a combination of success-biased and conformist or unbiased transmission, this result holds with larger n . Assuming social learning has reached fixation, the increase in a population’s mean skill level is lower if cumulative culture is initially absent than initially present, if population size is finite, or if cultural transmission has a frequency-dependent component. Hence, multiple barriers to cultural accumulation may explain its rarity. This article is part of the theme issue ‘Human socio-cultural evolution in light of evolutionary transitions’.

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“…Our model of conformity to a polychotomous trait generalizes the dichotomous trait model of Boyd and Richerson ( 2 ), which has been widely used in previous theoretical studies of conformity ( 14 – 21 , 24 , 26 ). Dichotomous traits have two variants, such as pro/con, skilled/unskilled, or cooperate/defect, whereas polychotomous traits, such as baby names, art motifs, or birdsong syllables, have three or more variants.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, incorporating nonrandom choices of the n role models (e.g., family, close friends, or prestigious individuals) would likely produce different population dynamics that would be interesting to explore. Finally, temporal variation in conformity coefficients has recently been incorporated into the dichotomous trait model ( 26 ), and it would be interesting to explore the consequences of such variation in the polychotomous case.…”

Section: Discussionmentioning

confidence: 99%

“…In ref. 26 , further generalizations allowed conformity coefficients to vary stochastically over time.…”

mentioning

confidence: 99%

“…For example, if the name “Mary” is slightly more popular than other names, an individual might conform and name a child Mary, but it would be unrealistic to expect the same level of conformity if, say, 80% of all people that the individual observed were named Mary. Our previous studies ( 25 , 26 ) focused on dynamical properties of the commonly studied model ( 2 ) of a dichotomous trait, which could include multiple conformity coefficients if

role models were sampled. Here we generalize ref.…”

mentioning

confidence: 99%

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Polychotomous traits and evolution under conformity

Denton

¹

,

Liberman

²

,

Feldman

³

2022

Proc. Natl. Acad. Sci. U.S.A.

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Conformist and anticonformist transmission of dichotomous cultural traits (i.e., traits with two variants) have been studied both experimentally, in many species, and theoretically, with mathematical models. Signatures of types of conformity to polychotomous traits (with more than two variants; e.g., baby names and syllables in bird song) have been inferred from population-level data, but there are few models that include individual-level biases among more than two discrete variants. We generalize the standard dichotomous trait conformity model by Boyd and Richerson to incorporate n ≥ 3 role models and m ≥ 2 variants. Our analysis shows that in the case of n=3 role models, under anticonformity, the central polymorphic equilibrium p * = ( 1 m , … , 1 m ) is globally stable, whereas under conformity, if initially the frequencies of ℓ variants are all equal to the maximum variant frequency in the population, there is global convergence to an equilibrium in which the frequencies of these variants are all 1 ℓ and all other variants are absent. With a general number n of role models, the same result holds with conformity, whereas under anticonformity, global convergence is not guaranteed, and there may be stable frequency cycles or chaos. If both conformity and anticonformity occur for different configurations of variants among the n role models, a variety of novel polymorphic equilibria may exist and be stable. Future empirical studies may use this formulation to directly quantify an individual’s level of (anti)conformist bias to a polychotomous trait.

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