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The evolution and function of imitation in animal learning has always been associated with its crucial role in cultural transmission and evolution. Can imitation evolve in the absence of cultural transmission? We investigate a model of a semelparous organism with discrete, nonoverlapping generations in which the sole transmission of information between generations is genetic. We suppose that an organism can modify its phenotype in response to the phenotypes it observes in its cohort of conspecifics. We find that during a period of directional selection towards a phenotypic optimum, natural selection favors modifiers which cause an organism to bias its plastic phenotype in the direction \emph{opposite} to the mean phenotype of the population. As the population approaches the phenotypic optimum and shifts into stabilizing selection, selection on the modifier reverses and favors strong imitation of the population mean. Imitation can become so strong that ``genotype-phenotype disengagement&#39;&#39; occurs (Gonzalez, Watson, and Bullock 2017), and for multivariate phenotypes evolution can cycle between genotype disengagement and re-engagement. While in some cases the evolution of imitation and anti-imitation increase the mean fitness of the population, cycles of genotype disengagement and re-engagement can make the mean fitness nonmonotonic in time.

Cultural Evolution Society 2021

The Evolution of Imitation Without Cultural Transmission

### 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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&nbsp; 
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 **Hiromi Matsumae**:	matsumae.hiromi.g@tokai.ac.jp
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 **Sarah Mathew**:	Sarah.Mathew@asu.edu
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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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The evolution and function of imitation in animal learning has always been associated with its crucial role in cultural transmission and evolution. Can imitation evolve in the absence of cultural transmission? We investigate a model of a semelparous organism with discrete, nonoverlapping generations in which the sole transmission of information between generations is genetic. We suppose that an organism can modify its phenotype in response to the phenotypes it observes in its cohort of conspecifics. We find that during a period of directional selection towards a phenotypic optimum, natural selection favors modifiers which cause an organism to bias its plastic phenotype in the direction \emph{opposite} to the mean phenotype of the population. As the population approaches the phenotypic optimum and shifts into stabilizing selection, selection on the modifier reverses and favors strong imitation of the population mean. Imitation can become so strong that ``genotype-phenotype disengagement'' occurs (Gonzalez, Watson, and Bullock 2017), and for multivariate phenotypes evolution can cycle between genotype disengagement and re-engagement. While in some cases the evolution of imitation and anti-imitation increase the mean fitness of the population, cycles of genotype disengagement and re-engagement can make the mean fitness nonmonotonic in time.

technical paper

In this study, we used three years of house finch (Haemorhous mexicanus) song recordings spanning four decades in the introduced eastern range to assess how individual-level cultural transmission mechanisms drive population-level changes in birdsong. First, we developed an agent-based model (available as a new R package called TransmissionBias) that simulates the cultural transmission of house finch song given different parameters related to transmission biases, or biases in social learning that modify the probability of adoption of particular cultural variants. Next, we used approximate Bayesian computation and machine learning to estimate what parameter values likely generated the temporal changes in diversity in our observed data. We found evidence that strong content bias, likely targeted towards syllable complexity, plays a central role in the cultural evolution of house finch song in western Long Island. Frequency and demonstrator biases appear to be neutral or absent. Additionally, we estimated that house finch song is transmitted with extremely high fidelity. Future studies should use our simulation framework to better understand how cultural transmission and population declines influence song diversity in wild populations.

Content bias in the cultural evolution of house finch song

Human culture is considered to be different from animal culture due to its communicative and interactive nature built on shared intentionality and cognitive flexibility. Here, we investigated whether chimpanzees use communication and show behavioral indications of their joint commitment to engage in cultural practices by analyzing grooming handclasp (GHC) interactions – a socio-cultural behavior for which coordination is required. In a GHC two apes engage in a joint action leading to a symmetrical postural configuration in which each of the partners extends an arm overhead and clasps the other's wrist or hand. Previous accounts attributed the enactment of GHC to behavioral shaping whereby the initiator physically molds the arm of the partner into the GHC posture. Using frame-by-frame analysis and matched-control methodology, we find that chimpanzees use gestural communication to entice group members into GHC. The use of communication instead of physical shaping to initiate GHC requires an active and highly synchronized response from the partner, which showcases a behavioral expression of joint commitment to engage in this shared cultural practice. Moreover, we show that GHC initiators used a variety of initiation strategies, which attests to their situation-contingent interactional flexibility. We conclude that chimpanzees can be jointly committed to a cultural practice, which suggests that culture predicated on shared intentionality and flexible communication may not be unique to the human species.

Chimpanzees communicate to coordinate a cultural practice

Music, dance, and other performing arts are cultural universals that are found in all societies but that vary within and between them. The lack of standardized cross-cultural databases has impeded scientific understanding of global variation in the arts. We introduce the Global Jukebox (theglobaljukebox.org) as a resource for comparative and cross-cultural study of the performing arts and culture. Its core is the Cantometrics dataset, encompassing standardized codings on 37 aspects of musical style for 5,783 traditional songs from 991 societies. The Cantometrics dataset has been thoroughly cleaned and checked for reliability and accuracy. Eight additional datasets code elements of instrumentation, conversation, popular music and other aspects of expressive culture. For the first time, all digitized Global Jukebox data is being made available in open-access, machine-readable format, linked with streaming audiovisual files to the maximum extent allowed while respecting copyright and the wishes of culture-bearers. The data is cross-indexed with two leading cross-cultural databases: the Database of Peoples, Languages, and Cultures (D-PLACE) and eHRAF World Cultures. This allows researchers to test hypotheses about worldwide aesthetic patterns and traditions. We will use modern phylogenetic comparative methods to reanalyze the original proposals by Alan Lomax and his research team regarding coevolutionary relationships between the performing arts, social structure, and human history. The Global Jukebox adds a large and detailed global database of the performing arts to enrich our understanding of the science of human cultural diversity.

The Global Jukebox: A Public Database of Performing Arts and Culture

Music - like language - is a human cultural universal that displays considerable cross-cultural variation and historical continuity. But while hypotheses about language (co)evolution have been tested against large cross-cultural databases, hypotheses about music have not, principally because no such databases have been publicly available. We take advantage of a new public database of 5,783 songs from 991 societies coded for 37 “Cantometric'' features of musical style (theglobaljukebox.org; cf. Wood et al., this conference) to test three sets of pre-registered hypotheses about music-culture coevolution: 

1) What is the primary determinant of musical style: song structure or social context?
2) What is the primary determinant of musical distribution: genetic history, language history, or geography?
3) What is the primary social determinant of musical style: economic subsistence or kinship intensity?

Each set of hypotheses helps us paint a more complete picture of music's role in the cultural past of human evolution. We will test these competing hypotheses using latent variable modelling and phylogeographic methods, combining the Global Jukebox database of music codings with language phylogeny, genetic distances (GeLaTo), and social structure (Ethnographic Atlas; D-PLACE.org). By tying these strands of evidence together we will present a comprehensive and quantitative understanding of global music diversity and its role in the history of human society.

Testing hypotheses of music-culture coevolution with a global sample of 5,783 songs

Precolumbian South America offers a rich subject of investigation of cultural macroevolution, given the multiple innovations and transformations that document unique or parallel patterns to those of other parts of the world. One can thus examine the relation of cultural phenomena to language groups and population history, and issues such as trans-pacific diffusion or exchange among major areas (e.g., Andes, Amazon). Comparative musicology of songs has greatly developed – we extend this to the study of material culture. We examined organological data, extracted from archaeological and ethnographic sources, and produced new continental databases (e.g., matrix of 57 aerophones, membranophones and idiophones in 145 societies based largely on Izikowitz’ work) and analysed them. South Americans developed a high diversity of wind instruments and drums, while lacking chordophones. Our network analysis of panpipe features identified four clusters: two each in the Tropical Forest and Andean regions. About forty percent of the instruments in the standard organological classification are present in the archaeological, but not in the ethnographic record. The archaeological record comes mostly from the central Andean region, reflecting both preservational biases and research efforts, but we report on records from other areas. Our work represents the first analysis of cultural artifacts at a continental scale, and outline possible evolutionary paths by linking the instruments to the populations who produced them. This effort can be further developed by curating and standardizing resources from catalogues and museum collections, a task in great need of development in South American institutions.

Cultural macroevolution of musical instruments in South America

There is a long-standing debate considering the possibility of sympatric speciation, the origin of multiple species from one, without geographic isolation. Although the central position of the geographical aspect of speciation had suffered significant demise recently, spatial isolation is still believed to play a pivotal role in divergent evolution by limiting gene flow between adjacent populations. Here we present a novel model combining assortative mating and multidimensional inheritance. The continuous inheritance between interacting agents can approximate additive genetic (Galton-Pearson model) or social (Parental Variability-Dependent Inheritance) transmission, or a combination of the two. We demonstrate that in a model where variance of inputs is proportional to the variance of outputs, the assortment alone can lead to the formation of distinct, cohesive clusters of individuals with low within-group and large between-group variability even in the absence of disruptive natural or cultural selection.
Subcultures can, therefore, emerge even without the preferential imitation of self-similar individuals. All it takes is the negative relationship between the probability of interaction and the distance in the culture-space.
The model explains the constant and frequent sympatric emergence of subcultures and varieties with limited gene flow that can only later diverge ecologically and possibly speciate. This model might be particularly relevant for taxa with a high capacity for cultural evolution, such as cetaceans, songbirds, and hominins, known for their increased potential to undergo adaptive ecological radiation.

Assortative interaction leads to the emergence of subcultures even without selective imitation

In this paper I depart from the traditional Price-equation formulation of multilevel selection and introduce a new theoretical approach of a multi-level selection process where phases of intra-group interactions alternate with phases of interaction among groups. I assume that a given genetic allele or cultural trait is maladaptive for individuals bearing it but increases the fitness of others in the same group (like altruism), but groups with a higher fraction of bearers of the trait have an advantage in the inter-group interaction phases and reproduce faster. Two main results are obtained that had remained somehow hidden in the traditional model: (1) For group selection to overcome the opposing effect of individual selection the key factor is the amount of “positive” variation in groups’ reproduction, not the strength of group selection per se. (2) Multilevel selection is vulnerable to invasion by mutants that inhibit the phenotypic effect of the allele or cultural trait in the intra-group phases but allow its expression in the between-group phases, in a similar process that make green beards genes unlikely to evolve. By discriminating its phenotypic effects depending on appropriate cues in both environments, the mutated trait restores the selfish behavior when it serves the individual but maintains the altruistic effect when it serves both the group and the individual. This can be interpreted as breaking the “public good” link of the original allele or trait regarding its positive effect in the inter-group competition in relation to its detrimental effects in the intra-group competition phases.

Selection pressures against multilevel selection

A key condition for cultural group selection to function is that substantial between-group variation is somehow maintained. It has been suggested that multiple social learning biases such as conformity and prestige-bias contribute to maintenance of intergroup variation by suppressing within-group variation. It has also been argued that such social learning biases are endowed to human beings because they are evolutionarily adaptive. However, it is not clear whether psychological mechanisms bolstering within-group homogeneity are adaptive in non-cooperative game settings. In the present study, we examined whether the frequency dependent preference which contributes to within-group behavioral homogeneity was evolvable in non-cooperative game settings. We then examined whether the frequency dependent preference could evolve and facilitate cooperation in tandem with the evolution of norm-internalization capacity, by extending the Gavrilets and Richerson (2017)’s agent-based simulation model on the evolution of norm-internalization. In making their decisions, individuals attempt to maximize a utility function that captures three distinct motives: maximizing material payoff, following the norms and the majority behavior. The second motive depends on one’s ability to internalize the norm, and the third one depends on one's sense of conformity. We formulated frequency dependent utility functions in two different ways and found that any type of frequency dependent preferences was not favored by natural selection, while the ability to internalize norms could evolve under a wide range of conditions and promote the evolution of cooperation.

The coevolution of norm-internalization and frequency dependent preferences through cultural group selection

Low rates of data availability and results reproducibility have been observed across the biological and behavioural sciences. Here, we attempt to quantify the rate of reproducibility in the study of social learning research. We surveyed 560 empirical publications on this topic, published between 1955 and 2018 in animal behaviour, behavioural ecology, cultural evolution, and evolutionary psychology.

Data was recoverable online or through direct data requests for 30% of this sample. Data recovery declines exponentially with time since publication, halving every 6 years, and up to every 9 years for human experimental data. Essentially no data is available for any publication before the year 2000. However, when data for a publication is available, we estimate by hierarchical modeling a high probability of subsequent data usability (87%), analytical clarity (97%), and agreement of published results with reproduced findings (96%), giving an overall reproducibility rate of any given result in the literature of 23% [0.89 HPDI: 15-28%].

Our results suggest that the primary threat to the reproducibility of published results in cultural evolution is the lack of long-term data archiving, rather than mistakes in analyses or results. Although recent innovations in research transparency, such as the FAIR data guidelines and use of version-controlled analysis code, address these failure points, individual adoption of these novel research practices, as well as incentives promoting data reuse and openness at the funding and publication level, must become more widespread to prevent similar decay of social learning results in the future.

Estimating the reproducibility of social learning research, 1955-2018

Culturally transmitted traits that have deleterious effects on health-related traits can be regarded as cultural pathogens. A cultural pathogen can produce coupled dynamics with its associated health-related traits, so that understanding the dynamics of a health-related trait benefits from consideration of the dynamics of the associated cultural pathogen. Here, we treat anti-vaccine sentiment as a cultural pathogen, modelling its ‘infection’ dynamics with the infection dynamics of the associated vaccine-preventable disease. In a coupled susceptible–infected–resistant (SIR) model, consisting of an SIR model for the anti-vaccine sentiment and an interacting SIR model for the infectious disease, we explore the effect of anti-vaccine sentiment on disease dynamics. We find that disease endemism is contingent on the presence of the sentiment, and that presence of sentiment can enable diseases to become endemic when they would otherwise have disappeared. Furthermore, the sentiment dynamics can create situations in which the disease suddenly returns after a long period of dormancy. We study the effect of assortative sentiment-based interactions on the dynamics of sentiment and disease, identifying a tradeoff whereby assortative meeting aids the spread of a disease but hinders the spread of sentiment. Our results can contribute to finding strategies that reduce the impact of a cultural pathogen on disease, illuminating the value of cultural evolutionary modelling in the analysis of disease dynamics.

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