Japan

Military personnel in industrialized societies often develop posttraumatic stress disorder (PTSD) during combat. It is unclear whether combat-related PTSD is a universal evolutionary response to danger or a culture-specific syndrome of industrialized societies. We interviewed 218 Turkana pastoralist warriors in Kenya, who engage in lethal cattle raids, about their combat experiences and PTSD symptoms. Turkana in our sample had a high prevalence of PTSD symptoms, but Turkana with high symptom severity had lower prevalence of depression-like symptoms than American service members with high symptom severity. Symptoms that facilitate responding to danger were better predicted by combat exposure, whereas depressive symptoms were better predicted by exposure to combat-related moral violations. The findings suggest that some PTSD symptoms stem from an evolved response to danger, while depressive PTSD symptoms may be caused by culturally specific moral norm violations.

Cultural Evolution Society 2021

Combat stress in a small-scale society suggests divergent genetic and cultural roots of PTSD symptoms

## Welcome!
"I am excited to welcome you to this year’s edition of the Conference on Empirical Methods in Natural Language Processing! Importantly, it marks the 30th edition of EMNLP. With over 8,000 submissions, more than 3,000 accepted papers, and thousands of attendees, we have come a long way from that first
workshop, which had 14 accepted papers. As the field looks ahead, Suzhou is the fitting location for celebrating this milestone: rooted in a long literary tradition, yet modern and forward-looking, and home to a large share of the NLP community." 

*Message from the General Chair, Dirk Hovy*

EMNLP 2025

Celebrate 30 Years of EMNLP! 
EMNLP 2025 will be held in Suzhou, China from November 5th to November 9th, 2025.

technical paper

### 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.

### Schedule and Program

[![](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)
[![](https://assets.underline.io/uploads/markdown_image/1/image/12285eb22580949635121d15d5b46325.png)](https://www.chain.hokudai.ac.jp/CES2020/wp-content/uploads/2021/06/abstracts.pdf)

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### Organizing committee

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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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For attending the conference, you first need to register and pay fees from [the link here](https://www.chain.hokudai.ac.jp/CES2020/registration/). After the payment of the registration fees, you will receive a ticket, which is necessary for accessing the conference site. After the payment of the registration fees, you will receive a ticket, which is necessary for accessing the conference site

Registration fee

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.

Modelling anti-vaccine sentiment as a cultural pathogen

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.

The Evolution of Imitation Without Cultural Transmission

The discovery of complex culture in different species is a major interest in cultural evolution research, with work so far uncovering evidence for cultural traits in some species of primates (e.g., baboon, chimps), whales (e.g., killer whales, humpback whales), and birds (e.g., Caledonian crow). Here, we offer a new animal model for studying culture evolution: The Elephant. Specifically, we present evidence that elephants possess many of the prerequisites associated with cultural evolution, including tool use, social learning, language, and complex community structure. For example, there is evidence of cultural learning in elephants, as they are able to acquire specific techniques for exploiting specific resource sites merely by observing conspecifics and by practicing and exploring new behaviors by themselves. Crucially, we argue that elephants have gone through a similar evolutionary process as humans - self-domestication - which is at the heart of our ability for cultural niche construction and the sophistication of language through cultural evolution. We use cross-species comparison and genetic analyses to show that elephants display the cognitive, behavioral, and physiological features that are associated with self-domestication, including changes in the brain, cortisol sensitivity to the social environment, reduced reactive aggression, and extended juvenile period. Moreover, elephants might stand as the only case of self-domestication outside the primate group, i.e., domestication that happened organically without human intervention. As such, it is a powerful model for investigating questions regarding language evolution and how convergent evolution of cultural learning can result in similar cognitive and communicative abilities.

Elephants as a new animal model of cultural evolution resulting from self-domestication

Sperm whales (Physeter macrocephalus) are cetaceans with a worldwide distribution and a complex social structure. Sperm whales are members of cultural groups, called “vocal clans”. Members of a vocal clan have a distinctive suite of socially learned social calls, and do not associate with individuals from other vocal clans. However, whether vocal clan membership has implications beyond the use of a characteristic acoustic repertoire had never been tested in the Caribbean. Via a dedicated survey of sperm whales in the Lesser Antilles, we observed stark differences in vocal clan distributions across relatively small distances (<100km), with little to no overlap between them. These differences in distribution appear to relate to environmental variables with one vocal clan preferring island channels and areas of high eastward current speed and the other preferring canyons with low meridional velocity variance. Such fine-scale habitat partitioning is surprising for a species which is often referred to as an “ocean nomad” and contrasts with Eastern Tropical Pacific clans, which share habitats over much greater scales (we observe a factor of 10 difference between the movements of Eastern Caribbean and Eastern Tropical Pacific sperm whales). We hypothesize that Eastern Caribbean sperm whales are habitat specialists, with vocal clans specializing on the use of certain environmental features and maintaining this specialization through social learning. This not only highlights the need to incorporate culture in the field of conservation management, as different cultural groups have different distributions and habitat use, but also the inherent ties between culture and the environment.

Culture impacts the distribution and habitat use of sperm whales in the Eastern Caribbean

This presentation will focus on two studies which looked at how individuals learn about, maintain and transmit different aspects of their cultures. Each study sampled 100 participants from three groups in the UK (50 British nationals including Black and White British, 25 Polish and 25 South Asian immigrants which are the largest immigrant groups). Both studies used mixed-methods surveys combining quantitative questions with freelists.

We looked at 3 types of cultural groups that our participants belong to: heritage, religious and national groups. Study 1 looked at which aspects of their cultures individuals believed are important to maintain, what motivated them to do so and the consequences of not maintaining these cultural practices. Study 2 looked at the aspects of these cultures individuals believed are important to teach to children and at what age. In both studies, we looked at how individuals have been taught about their various cultures, and what cultural domains they believed their cultural groups should, or should not assimilate from others and vice versa. 
We compare how these cultural domains vary in two ways: 
1. based on the type cultural group and
2. across the three demographic groups we are sampling. 

Data analysis for these studies is currently ongoing and will be completed in time for the presentation. Preliminary findings from the two studies show that the main sources for learning about one’s culture are family (parents and grandparents), school and media (TV, music and Social media). Some of the cultural aspects that are considered important fall under categories of functional domain (e.g food and music), cooperation (tolerance, acceptance, close knit ties), tradition (language, family traditions), history (of the countries, religions and movements such as immigration) and morality.

Transmission of Cultural Domains among Immigrants and British nationals in the UK

People often attribute rumours to an individual in a knowledgeable position two steps removed from them (a credible friend of a friend), such as ‘my friend’s father, who’s a cop, told me about a serial killer in town’. Little is known about the influence of such attributions on rumour propagation, or how they are maintained when the rumour is transmitted. In four studies (N = 1824) participants exposed to a rumour and asked to transmit it overwhelmingly attributed it either to a credible friend of a friend, or to a generic friend (e.g. ‘a friend told me about a serial killer in town’). In both cases, participants engaged in source shortening: e.g. when told by a friend that ‘a friend told me ...’ they shared the rumour as coming from ‘a friend’ instead of ‘a friend of friend’. Source shortening and reliance on credible sources boosted rumour propagation by increasing the rumours’ perceived plausibility and participants’ willingness to share them. Models show that, in linear transmission chains, the generic friend attribution dominates, but that allowing each individual to be exposed to the rumour from several sources enables the maintenance of the credible friend of a friend attribution.

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