Japan

Population size has long been considered an important driver of cultural change. Results from population genetics, however, demonstrate that it is not the census population size, N, but the effective size of a population, N_e, that determines important evolutionary parameters. This effective population size governs the rate of change in a population due to drift and affects genetic variability both within and between populations. Here, we systematically examine effective population sizes for traits that evolve culturally, i.e. through processes of innovation and social learning, rather than genetically. We use different modeling approaches to investigate how cultural N_e and levels of diversity depend on the way traits are learned, population connectedness and social network structure. We show that one-to-many and frequency-dependent transmission can temporally or permanently lower effective population size compared to census numbers. Contrary to expectations in the literature, migration does not increase N_e and a process of cultural exchange among groups increases only the less meaningful inbreeding effective number but not the variance effective number. While network density in random networks leaves N_e unchanged, scale-free networks tend to decrease and small-world networks tend to increase N_e compared to census numbers. Finally, for one-to-many transmission and different network structures, effective size and cultural diversity are closely associated. For connectedness, however, small amounts of migration and cultural exchange result in highest diversity independently of N_e. Our results highlight the importance of effective population size for cultural evolution and show that inferring N_e requires detailed knowledge about underlying cultural and demographic processes.

Cultural Evolution Society 2021

Effective population size for culturally evolving traits

### Conference Welcome

Welcome to the third Cultural Evolution Society Conference, CES2021. In the conference, which will be held from June 9-11, 2021, about 180 researchers from East Asia, Oceania, Middle East, Europe, North and South America give presentations on their latest research advancing the evolutionary understanding of human and nonhuman animal culture.

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[![](https://assets.underline.io/uploads/markdown_image/1/image/1ef06ffd05f80957b4a5b685f63ee3ba.png)](https://www.chain.hokudai.ac.jp/CES2020/wp-content/uploads/2021/06/fullprogram.pdf)
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See the full details of [the code of conduct](https://www.chain.hokudai.ac.jp/CES2020/code-of-conduct/).
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 **Hiromi Matsumae**:	matsumae.hiromi.g@tokai.ac.jp
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**Scientific Committee:** [Kenichi Aoki (Meiji University)](https://sites.google.com/site/kenichi1aoki/home), [Yasuo Ihara (the University of Tokyo)](https://researchmap.jp/read0209180?lang=en), [Hiromi Matsumae (Tokai University)](https://sites.google.com/site/hiromimatsumae/eng), [Naoko Matsumoto (Okayama University)](https://researchmap.jp/nmatsumoto_okayama-u), [Masako Myowa (Kyoto University)](https://myowa.educ.kyoto-u.ac.jp/en), [Hisashi Nakao (Nanzan University)](https://www.hisashinakao.com/), [Patrick E. Savage (Keio University)](https://sites.google.com/view/comp-music-lab/home)

**Local Organizing Committee:** [Yutaka Horita (Teikyo University)](https://sites.google.com/site/yhoritapage/), [Masanori Takezawa (Hokkaido University)](https://lalalarakko.github.io/), [Ayaka Takimoto (Hokkaido University)](https://lynx.let.hokudai.ac.jp/~takimoto/), [Kohei Tamura (Tohoku University)](https://researchmap.jp/7000017854)

**Inclusiveness Committee:** [Sarah Mathew (Arizona State University)](https://www.sarahmathew.net/), [Hiromi Matsumae (Tokai University)](https://sites.google.com/site/hiromimatsumae/eng), [Patrick E. Savage (Keio University)](https://sites.google.com/view/comp-music-lab/home)


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technical paper

Overimitation is defined by a tendency to copy all actions executed by a model, even the clearly irrelevant ones. The motivational mechanisms and functionality of overimitation are still not well understood, but its possible adaptive meaning could be related to causal opacity of a great part of socially learned behaviors. This phenomenon has been widely replicated in several contexts and has been observed in the behavior of children over 2 years of age and even in adults. Studies have shown that overimitation is sensitive to some characteristics of the model observed such as age, familiarity, proficiency, and reputation. Our work intended to investigate the effect of information about the competence of an adult model on the copying of irrelevant actions by preschool children (5 years old) in a task. We tested the influence of self-declared information about the model competence and of the same kind of information given by third parties in a conversation about the model. Our results reveal no effect of both ‘‘self-declared competence” and ‘‘reputation” biases on overimitation. We discuss that this result may have occurred because other information available to participants, and not manipulated by us, was used to infer model competence such as the model’s age and success in the task directly observed by the participants. Another potential explanation is that children use a ‘‘copy all, correct later” strategy in a context where only one model is available.

Biases on social learning: the effect of model's competence on children's overimitation

Living in a social group confers an individual many advantages, one being the possibility to obtain relevant information from others. However, one must be able to discriminate what is useful. For instance, human and non-human primates must know who and what to learn from. Here, we investigated the opportunities to obtain visual information from the face of others, which we call VAF (Visual Access to Faces) in a wild population of capuchin monkeys from Brazil. We looked at four infants, aged two and nine months old and aimed at testing the hypothesis that both the identity of the individual the infants were having VAF from and the infants’ age influenced the duration of these opportunities to obtaining information from others’ faces. We looked at 323 VAF events (mean=2.539 seconds±0.489). We used a GLMM (infants as a random factor) including duration of VAFs as dependent variable and individual with whom the VAF occurred and month (2nd or 9th) as fixed factors. We found that the identity of the other monkey was not significant, neither its interaction with month. However, month alone was significant (p=0.016), with a higher mean for the 2nd (3.296±0.653) than the 9th (1.415±0.560) month. From these results it appears that whom the infant is looking at is not relevant, however "when", if earlier or later in infancy, is critical for the acquisition of this sort of social information. That is, accessing and processing this type of visual information provided by faces may be an initial social development pattern. 

Keywords: Sapajus libidinosus, social behaviour, social cognition, social regulation, visual processing 

Funding: Fapesp

Looking at others’ faces may be more important in early infancy

Humans have adapted well to diverse environments in part because of their ability to efficiently acquire information from their social environment. However, we still know very little as to how young children acquire cultural knowledge, and in particular the circumstances under which children prioritize social over asocial learning. In this study we ask whether children will selectively adopt either a majority-biased or a payoff-biased social learning strategy in the presence or absence of asocial learning. Three- to 5-year-old children (n = 117) were first shown a video in which four other children took turns in retrieving a capsule housing a reward from one of two boxes. Three of the children (the ‘majority’) retrieved a capsule from the same box and a single individual (the ‘minority’) retrieved a capsule from the alternative box. Across four conditions we manipulated both the value of the rewards available in each box (equal or unequal payoff), and whether children had knowledge of the payoff before making their own selection. Results show that children adopted a majority-biased learning strategy when they were unaware of the value of the rewards available, but adopted a payoff-biased strategy when the payoff was known to be unequal. We conclude that children are strategic social learners who use both social and asocial learning to maximize personal gain.

The ontogeny of selective social learning: Young children flexibly adopt majority or payoff-based biases depending on task uncertainty

Modern human culture relies on copying of behavioural forms beholden to past cultural evolution. It remains debated whether such ‘action copying’ underlies any wild ape culture. It is unclear whether this ability was present in the last common ancestor or whether it first appeared after their divergence. Evidence of untrained apes spontaneously copying novel action forms, under controlled conditions, would favour the ‘copying hypothesis’, this data is lacking. Given that majority influence appears to affect ape social learning, we hypothesised that the dearth of evidence, in untrained apes, could be due to a lack of majority demonstrations in research. If evidence were found, in such a population, this would lend credence to the argument that wild apes and even the last common ancestor, had the capacity to spontaneously copy novel actions. Here, we performed the first controlled, action copying study that incorporated majority-bias with untrained non-human great apes (all species; n=19). Our results show a total lack of copying ability, all untrained mother-reared apes failed to copy, or approximate, the demonstrated action forms, despite majority demonstrations. Our findings reinforce the view that apes do not spontaneously copy action forms - not even majority demonstrations changed this empirically-grounded picture. Our finding also adds to increasing evidence that wild ape cultures are never, or very rarely, based on action form copying. This also means that action form copying likely arrived in the human lineage - after the divergence from the last common ancestor.

Can apes ape? What about with the addition of biases?

It has become increasingly clear that culture and social learning play a vital role in species ecology. While much attention has been paid to its presence in vertebrates such as primates and cetaceans, which often have complex social structure, it also occurs in a broad and diverse variety of animal communities including reptiles, fishes, and insects. As we learn more about the breadth of species that utilise social learning, it has expanded the scope of what social learning and culture can tell us beyond a single species. This is particularly relevant as the conservation value of culture and social complexity becomes more established. Here I review social learning across species with varying community structures, providing an overview of how culture can manifest across animal societies and the different ecological roles it may play as a result. Such a review is critical to how studies across different species and community structures may inform one another. It further illustrates the intrinsic value of animal culture in practice as well as theory. When these separate pieces are brought together, they will provide the necessary infrastructure to move the field of animal culture forward in how it can be both understood and applied.

The diversity of animal culture across community structures

Envy-based magic beliefs, including witchcraft, are prevalent in societies around the world. These beliefs can create distrust due the belief that one’s misfortune can be magically caused by others in their community. We examined the relationship between witchcraft rituals, motivation, and distrust in a sample of 428 Hindus Mauritians. Despite these beliefs being largely taboo, Hindu Mauritians have a pervasive belief in witchcraft and evidence of the performance of witchcraft rituals is readily found throughout Mauritius. Participants were shown a picture of fruits claimed to be purchased for a religious or witchcraft ritual or to be eaten, and given one of three motivations for the purchaser (envy, selfishness, or neutral). Participants in the witchcraft and envy conditions rated the purchaser as less trustworthy and more harmful to the community than in the other conditions. Participants who were told the purchaser was envious or selfish were more likely to accuse the purchaser of witchcraft even when told he was buying fruit for a religious ritual or to eat. Free list questions confirmed that envy as a motivation increased participants willingness to see this person as less trustworthy and to claim his actions will have negative reputational impacts and cause harm. This work suggests that a belief that others are practicing magic decreases trust and is believed to cause harm across motivations. Further, the claim that a person is envious or selfish can increase the willingness to make a witchcraft accusation.

Witchcraft, Envy, and Trust among Hindu Mauritians

Magic is of longstanding interest to researchers studying the cultural evolution of religion, philosophy, and even science. Recent research supports that magical thinking tendencies affect individuals' susceptibility to modern day misinformation, which suggests insights on the cultural evolution of magic may have policy applications today. Using newly collected survey and comparative datasets, I test three leading hypotheses for the cultural evolution of magic, 1) unilineal replacement of magic first by religion and then by science, 2) magic functioning to provide market goods that are distinct from religion or science, and 3) magic arising from long-evolved cognitive tendencies that constrain human psychology. I find empirical support for all three hypotheses but in differing contexts. Thus, rather than evolving through any single process, magical beliefs and practices appear to be induced through multiple processes of cultural evolution. Greater awareness of the contexts in which magical thinking operates, and when it may be adaptively useful, may allow people to better guard against misfiring of magical thinking that can result in the spread of scientific and journalistic misinformation.

Multiple socio-cognitive processes lead to the cultural evolution of magic

We propose an evolutionary model of the origin of ritual behavior in the hominin lineage that treats collective ritual as a communication technology facilitating mutualistic cooperation. In our model, we first synthesize the literature dealing with hunter-gatherer ethnography and hominin archaeology and identify gradual coalescence of similarity signals, coalitionary signals, and signals of commitment to collective action as the main building blocks of human ritual behavior. Subsequently, we turn to primatology and paleoanthropology to trace the presence of these signals in both non-human primates and past hominins. Adding the proximate level to our analysis, we pinpoint distinctive neurocognitive mechanisms scaffolding the three types of ritual signals (overimitation, shared intentions, recursiveness, prospection, cross-domain association) and track down their presence in past hominins. Finally, we connect this evidence with the prevalent socio-ecological selective pressures for cooperative communication (environmental variability, interdependence, inter-group interactions) and offer estimates both for when the first of the ritual signals started to evolve as well as when ritual signals coalesced into an adaptation affording to overcome collective action problems.

Origin of human ritual behavior

Religious belief is declining in many regions of the world, but some societies have remained highly religious. What explains why people and countries abandon their beliefs while others stay faithful to their religion? We propose that the Moralization of Religiosity (MoR)—the belief that religion is necessary and essential for morality—is key to answering this question. MoR likely emerged as a by-product of the historical rise of prosocial religions, but we propose that it has an additional side-effect—it discourages deconversion due to perceived reputational costs. We further suggest that cultural differences in MoR foreshadow patterns of nation-level secularization and individual-level deconversion. Our model is supported by historical cross-cultural, retrospective longitudinal, survey, and experimental studies. Study 1 (N = 218,603) shows that cross-cultural differences in MoR in 44 nations predict why some countries secularized faster than others from 1995-2014. Study 2 (N = 701) shows that childhood exposure to MoR predicts a stronger likelihood to maintain religion across the lifespan, controlling for several other factors. In Studies 3a-3c (N3a = 299; N3b = 300; N3c = 325), present-day MoR negatively predicts participants’ likelihood of deconverting in the future. Study 4 (N = 513) showed that endorsement of MoR predicted prejudice towards deconverts and atheists, suggesting that MoR inhibits deconversion due to perceived reputational costs. Finally, Study 5 (N = 461) replicates our key findings with an experimental design.

Moralization of Religiosity Explains Worldwide Trends in Religious Belief

The present research investigates how psychological mechanisms and social network structures generate patterns of cultural change and diversity. The two psychological mechanisms studied here are cultural drift and indirect minority influence; the former is parameterized by an error rate and the latter by a leniency threshold. The patterns of cultural change are examined in terms of magnitude (small vs large), speed (gradual vs rapid), and frequency (frequent vs rare). Diversity and polarization in a society are examined in terms of global cultural variation (inverse Simpson index) and local neighborhood difference (Hamming distance). Key findings are that in networks with high connectivity or local community structures (complete, scale-free, random, and modular networks) cultural drift can produce a rapid, large, and rare pattern of cultural change (punctuated equilibrium), whereas in lattice or small world networks, it produces a more gradual change pattern. Indirect minority influence robustly produces a gradual, small, and frequent pattern of cultural change (gradualism) across various network structures. When cultural change occurs in social networks that have a modular community structure, indirect minority influence generates a regime of cultural diversity whereas cultural drift generates a polarized regime. Finally, cultural drift and indirect minority influence generate distinct tipping points for social change in different network structures, but prediction of whether and when cultural change emerges is difficult at tipping points in both cases.

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Effective population size for culturally evolving traits

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