Cultural traits operating in senders are driving forces of cultural evolution.

We introduce a mathematical model of cultural evolution to study cultural traits that shape how individuals exchange information. Current theory focuses on traits that influence the reception of information (receiver traits), such as evaluating whether information represents the majority or stems from a trusted source. Our model shifts the focus from the receiver to the sender of cultural information and emphasizes the role of sender traits, such as communicability or persuasiveness. Here, we show that sender traits are probably a stronger driving force in cultural evolution than receiver traits. While receiver traits evolve to curb cultural transmission, sender traits can amplify it and fuel the self-organization of systems of mutually supporting cultural traits, including traits that cannot be maintained on their own. Such systems can reach arbitrary complexity, potentially explaining uniquely human practical and mental skills, goals, knowledge and creativity, independent of innate factors. Our model incorporates social and individual learning throughout the lifespan, thus connecting cultural evolutionary theory with developmental psychology. This approach provides fresh insights into the trait-individual duality, that is, how cultural transmission of single traits is influenced by individuals, who are each represented as an acquired system of cultural traits.

Underappreciated features of cultural evolution.

Cultural evolution theory has long been inspired by evolutionary biology. Conceptual analogies between biological and cultural evolution have led to the adoption of a range of formal theoretical approaches from population dynamics and genetics. However, this has resulted in a research programme with a strong focus on cultural transmission. Here, we contrast biological with cultural evolution, and highlight aspects of cultural evolution that have not received sufficient attention previously. We outline possible implications for evolutionary dynamics and argue that not taking them into account will limit our understanding of cultural systems. We propose 12 key questions for future research, among which are calls to improve our understanding of the combinatorial properties of cultural innovation, and the role of development and life history in cultural dynamics. Finally, we discuss how this vibrant research field can make progress by embracing its multidisciplinary nature. This article is part of the theme issue 'Foundations of cultural evolution'.

Modelling cultural systems and selective filters.

A specific goal of the field of cultural evolution is to understand how processes of transmission and selection at the individual level lead to population-wide patterns of cultural diversity and change. Models of cultural evolution have typically assumed that traits are independent of one another and essentially exchangeable. But culture has a structure: traits bear relationships to one another that affect the transmission and selection process itself. Here, we introduce a modelling framework to explore the effect of interdependencies on the process of learning. Through simulations, we find that introducing a simple structure changes the cultural dynamics. Based on a basic filtering mechanism for parsing trait relationships, more elaborate cultural filters emerge. In a mostly incompatible cultural domain of traits, these filters organize culture into mostly (but not fully) consistent and stable systems. Incompatible domains produce small homogeneous cultures, while more compatibility increases size, diversity and group divergence. When individuals copy based on a trait's features (here, its compatibility relationships), they produce more homogeneous cultures than when they copy based on the agent carrying the cultural trait. We discuss the implications of considering cultural systems and filters in the dynamics of cultural change. This article is part of the theme issue 'Foundations of cultural evolution'.

Assessing uncertainties from physical parameters and modelling choices in an atmospheric large eddy simulation model.

In this study, we investigate uncertainties in a large eddy simulation of the atmosphere, employing modern uncertainty quantification methods that have hardly been used yet in this context. When analysing the uncertainty of model results, one can distinguish between uncertainty related to physical parameters whose values are not exactly known, and uncertainty related to modelling choices such as the selection of numerical discretization methods, of the spatial domain size and resolution, and the use of different model formulations. While the former kind is commonly studied e.g. with forward uncertainty propagation, we explore the use of such techniques to also assess the latter kind. From a climate modelling perspective, uncertainties in the convective response and cloud formation are of particular interest, since these affect the cloud-climate feedback, one of the dominant sources of uncertainty in current climate models. Therefore we analyse the DALES model in the RICO case, a well-studied convection benchmark. We use the VECMA toolkit for uncertainty propagation, assessing uncertainties stemming from physical parameters as well as from modelling choices. We find substantial uncertainties due to small random initial state perturbations, and that the choice of advection scheme is the most influential of the modelling choices we assessed. This article is part of the theme issue 'Reliability and reproducibility in computational science: implementing verification, validation and uncertainty quantification in silico'.

Clouds and Convective Self-Aggregation in a Multimodel Ensemble of Radiative-Convective Equilibrium Simulations.

The Radiative-Convective Equilibrium Model Intercomparison Project (RCEMIP) is an intercomparison of multiple types of numerical models configured in radiative-convective equilibrium (RCE). RCE is an idealization of the tropical atmosphere that has long been used to study basic questions in climate science. Here, we employ RCE to investigate the role that clouds and convective activity play in determining cloud feedbacks, climate sensitivity, the state of convective aggregation, and the equilibrium climate. RCEMIP is unique among intercomparisons in its inclusion of a wide range of model types, including atmospheric general circulation models (GCMs), single column models (SCMs), cloud-resolving models (CRMs), large eddy simulations (LES), and global cloud-resolving models (GCRMs). The first results are presented from the RCEMIP ensemble of more than 30 models. While there are large differences across the RCEMIP ensemble in the representation of mean profiles of temperature, humidity, and cloudiness, in a majority of models anvil clouds rise, warm, and decrease in area coverage in response to an increase in sea surface temperature (SST). Nearly all models exhibit self-aggregation in large domains and agree that self-aggregation acts to dry and warm the troposphere, reduce high cloudiness, and increase cooling to space. The degree of self-aggregation exhibits no clear tendency with warming. There is a wide range of climate sensitivities, but models with parameterized convection tend to have lower climate sensitivities than models with explicit convection. In models with parameterized convection, aggregated simulations have lower climate sensitivities than unaggregated simulations.

Segregation within school classes: Detecting social clustering in choice data.

We suggest a new method for detecting patterns of social clustering based on choice data. The method compares similar subjects within and between cohorts and thereby allows us to isolate the effect of peer influence from that of exogenous factors. Using this method on Norwegian register data, we address the question of whether students tend to cluster socially based on similar background. We find that common background correlates with making the same choices of curricular tracks, and that both exogenous preferences and peer influence matter. This applies to immigrant students from the same country, and, to some extent, to descendants of immigrants, but not to students from culturally similar countries. There are also small effects related to parents' education and income.

Risk of Postoperative Up Staging or Upgrading among Men with Low Risk Familial Prostate Cancer.

PURPOSE: We investigated whether men with biopsy verified, low grade cancer and a family history of lethal or advanced prostate cancer are at particularly high risk for harboring undetected high grade disease. MATERIALS AND METHODS: Upgrading and up staging of prostate cancer are common after prostatectomy. In a nationwide population based cohort we identified 6,854 men with low risk prostate cancer who underwent radical prostatectomy. Among these men 1,739 (25%) had a history of prostate cancer in a first-degree relative and 289 (4%) had a first-degree relative with lethal or advanced prostate cancer. RESULTS: Compared to men with no familial occurrence of prostate cancer, the odds ratio for the risk of up staging among men with a familial occurrence of high risk or lethal prostate cancer was 1.06 (95% CI 0.76-1.47). The corresponding odds ratio for upgrading was 1.17 (0.91-1.50). CONCLUSIONS: We found no association between family history of prostate cancer and up staging or upgrading after radical prostatectomy.

The connection between moral positions and moral arguments drives opinion change.

Liberals and conservatives often take opposing positions on moral issues. But what makes a moral position liberal or conservative? Why does public opinion tend to become more liberal over time? And why does public opinion change especially fast on certain issues, such as gay rights? We offer an explanation based on how different positions connect with different kinds of moral arguments. Based on a formal model of opinion dynamics, we predicted that positions better connected to harm and fairness arguments will be more popular among liberals and will become more popular over time among liberals and conservatives. Finally, the speed of this trend will be faster the better the position connects to harm and fairness arguments. These predictions all held with high accuracy in 44 years of polling on moral opinions. The model explains the connection between ideology and moral opinions, and generates precise predictions for future opinion change.

Aversive medical treatments signal a need for support: a mathematical model.

Ineffective, aversive and harmful medical treatments are common cross-culturally, historically and today. Using evolutionary game theory, we develop the following model to explain their persistence. Humans are often incapacitated by illness and injury, and are unusually dependent on care from others during convalescence. However, such caregiving is vulnerable to exploitation via illness deception, whereby people feign or exaggerate illness in order to gain access to care. Our model demonstrates that aversive treatments can counter-intuitively increase the range of conditions where caregiving is evolutionarily viable, because only individuals who stand to gain substantially from care will accept the treatment. Thus, contemporary and historical "ineffective" treatments may be solutions to the problem of allocating care to people whose true need is difficult to discern.

Diversity preferences among employees and ethnoracial workplace segregation.

Ethno-racial workplace segregation increases already existing ethno-racial inequality. While previous research has identified discriminatory employers as drivers of workplace segregation, this study addresses the role of the employees. Sociological and social psychological theory suggest that people prefer to surround themselves with people who positively confirm their social identity or who contribute with higher group status. Through web-based surveys, we measure employee attitudes and preferences concerning ethno-racial workplace diversity, to what extent they differ by ethnicity/race, and if they contain intersectional patterns. Thereafter, we use simulation models to analyze the consequences for workplace segregation that these preferences would have, if realized. The main survey results showed that all ethno-racial groups favored their own in-group as colleagues, especially European Americans. As a secondary choice, the respondents preferred the out-group with the highest labor market status. Intersectional patterns were identified, as minority women were preferred as colleagues over minority men. Our simulation model, based on the results of two surveys on stated vs. indirectly revealed preferences, showed that employee preferences were at best not diverse enough to desegregate workplaces. When based on the most common preferences (i.e. excluding a few outliers), the simulations even suggested that these preferences can cause segregation. We relate these findings to Schelling's model of segregation.

Concordance of Non-Low-Risk Disease Among Pairs of Brothers With Prostate Cancer.

Purpose Prostate cancer among first-degree relatives is a strong risk factor for diagnosis of prostate cancer, and the contribution of heritable factors in prostate cancer etiology is high. We investigated how the concordance of non-low-risk prostate cancer among brothers is affected by their genetic relation. Methods We identified 4,262 pairs of brothers with prostate cancer in the Prostate Cancer Database Sweden. Their cancers were categorized as low risk (Gleason score ≤ 6; clinical stage T1-2, Nx/N0, Mx/M0; and prostate-specific antigen ≤ 10 ng/mL) or non-low risk. The odds ratio (OR) for concordance of non-low-risk cancer was calculated with logistic regression for the different types of fraternity (monozygotic twins, dizygotic twins, full brothers, and half-brothers) Results Among monozygotic twins who both were diagnosed with prostate cancer, the OR for both brothers being in the non-low-risk category was 3.82 (95% CI, 0.99 to 16.72) after adjusting for age and year of diagnosis. Among full brothers, the corresponding adjusted OR was 1.21 (95% CI, 1.04 to 1.39). When the analysis was restricted to brothers who both were diagnosed within 4 years, the results were similar. Conclusion Non-low-risk prostate cancer has a heritable pattern suggesting shared genetic factors, with the highest concordance among monozygotic twins. Our results suggest that a man whose brother has been diagnosed with a non-low-risk prostate cancer is at a clinically relevant increased risk of developing an aggressive prostate cancer himself.

Quantification of complex modular architecture in plants.

Morphometrics, the assignment of quantities to biological shapes, is a powerful tool to address taxonomic, evolutionary, functional and developmental questions. We propose a novel method for shape quantification of complex modular architecture in thalloid plants, whose extremely reduced morphologies, combined with the lack of a formal framework for thallus description, have long rendered taxonomic and evolutionary studies extremely challenging. Using graph theory, thalli are described as hierarchical series of nodes and edges, allowing for accurate, homologous and repeatable measurements of widths, lengths and angles. The computer program MorphoSnake was developed to extract the skeleton and contours of a thallus and automatically acquire, at each level of organization, width, length, angle and sinuosity measurements. Through the quantification of leaf architecture in Hymenophyllum ferns (Polypodiopsida) and a fully worked example of integrative taxonomy in the taxonomically challenging thalloid liverwort genus Riccardia, we show that MorphoSnake is applicable to all ramified plants. This new possibility of acquiring large numbers of quantitative traits in plants with complex modular architectures opens new perspectives of applications, from the development of rapid species identification tools to evolutionary analyses of adaptive plasticity.

Using register data to deduce patterns of social exchange.

This paper presents a novel method for deducting propensities for social exchange between individuals based on the choices they make, and based on factors such as country of origin, sex, school grades and socioeconomic background. The objective here is to disentangle the effect of social ties from the other factors, in order to find patterns of social exchange. This is done through a control-treatment design on analysing available data, where the 'treatment' is similarity of choices between socially connected individuals, and the control is similarity of choices between non-connected individuals. Structural dependencies are controlled for and effects from different classes are pooled through a mix of methods from network and meta-analysis. The method is demonstrated and tested on Swedish register data on students at upper secondary school. The results show that having similar grades is a predictor of social exchange. Also, previous results from Norwegian data are replicated, showing that students cluster based on country of origin.

A novel technique to combine and analyse spatial and temporal expression datasets: A case study with the sea anemone Nematostella vectensis to identify potential gene interactions.

Understanding genetic interactions during early development of a given organism, is the first step toward unveiling gene regulatory networks (GRNs) that govern a biological process of interest. Predicting such interactions from large expression datasets by performing targeted knock-down/knock-out approaches is a challenging task. We use the currently available expression datasets (in situ hybridization images & qPCR time series) for a basal anthozoan the sea anemone N. vectensis to construct continuous spatiotemporal gene expression patterns during its early development. Moreover, by combining cluster results from each dataset we develop a method that provides testable hypotheses about potential genetic interactions. We show that the analysis of spatial gene expression patterns reveals functional regions of the embryo during the gastrulation. The clustering results from qPCR time series unveils significant temporal events and highlights genes potentially involved in N. vectensis gastrulation. Furthermore, we introduce a method for merging the clustering results from spatial and temporal datasets by which we can group genes that are expressed in the same region and at the time. We demonstrate that the merged clusters can be used to identify GRN interactions involved in various processes and to predict possible activators or repressors of any gene in the dataset. Finally, we validate our methods and results by predicting the repressor effect of NvErg on NvBra in the central domain during the gastrulation that has recently been confirmed by functional analysis.

Quantitative morphological analysis of 2D images of complex-shaped branching biological growth forms: the example of branching thalli of liverworts.

BACKGROUND: Many organisms such as plants can be characterized as complex-shaped branching forms. The morphological quantification of the forms is a support for a number of areas such as the effects of environmental factors and species discrimination. To date, there is no software package suitable for our dataset representing the forms. We therefore formulate methods for extracting morphological measurements from images of the forms. RESULTS: As a case study we analyze two-dimensional images of samples from four groups belonging to three species of thalloid liverworts, genus Riccardia. The images are pre-processed and converted into binary images, then skeletonized to obtain a skeleton image, in which features such as junctions and terminals are detected. Morphological measurements known to characterize and discriminate the species in the samples such as junction thickness, branch thickness, terminal thickness, branch length, branch angle, and terminal spacing are then quantified. The measurements are used to distinguish among the four groups of Riccardia and also between the two groups of Riccardia amazonica collected in different locations, Africa and South America. Canonical discriminant analysis results show that those measurements are able to discriminate among the four groups. Additionally, it is able to discriminate R. amazonica collected in Africa from those collected in South America. CONCLUSIONS: This paper presents general automated methods implemented in our software for quantifying two-dimensional images of complex branching forms. The methods are used to compute a series of morphological measurements. We found significant results to distinguish Riccardia species by using the measurements. The methods are also applicable for analyzing other branching organisms. Our software is freely available under the GNU GPL.

Women's rights in democratic transitions: A global sequence analysis, 1900-2012.

What determines countries' successful transition to democracy? This article explores the impact of granting civil rights in authoritarian regimes and especially the gendered aspect of this process. It argues that both men's and women's liberal rights are essential conditions for democratisation to take place: providing both women and men rights reduces an inequality that affects half of the population, thus increasing the costs of repression and enabling the formation of women's organising - historically important to spark protests in initial phases of democratisation. This argument is tested empirically using data that cover 173 countries over the years 1900-2012 and contain more nuanced measures than commonly used. Through novel sequence analysis methods, the results suggest that in order to gain electoral democracy a country first needs to furnish civil liberties to both women and men.

Cooperation and Shared Beliefs about Trust in the Assurance Game.

Determinants of cooperation include ingroup vs. outgroup membership, and individual traits, such as prosociality and trust. We investigated whether these factors can be overridden by beliefs about people's trust. We manipulated the information players received about each other's level of general trust, "high" or "low". These levels were either measured (Experiment 1) or just arbitrarily assigned labels (Experiment 2). Players' choices whether to cooperate or defect in a stag hunt (or an assurance game)--where it is mutually beneficial to cooperate, but costly if the partner should fail to do so--were strongly predicted by what they were told about the other player's trust label, as well as by what they were told that the other player was told about their own label. Our findings demonstrate the importance for cooperation in a risky coordination game of both first- and second-order beliefs about how much people trust each other. This supports the idea that institutions can influence cooperation simply by influencing beliefs.

Analysis of a spatial gene expression database for sea anemone Nematostella vectensis during early development.

BACKGROUND: The spatial distribution of many genes has been visualized during the embryonic development in the starlet sea anemone Nematostella vectensis in the last decade. In situ hybridization images are available in the Kahi Kai gene expression database, and a method has been developed to quantify spatial gene expression patterns of N. vectensis. In this paper, gene expression quantification is performed on a wide range of gene expression patterns from this database and descriptions of observed expression domains are stored in a separate database for further analysis. METHODS: Spatial gene expression from suitable in situ hybridization images has been quantified with the GenExp program. A correlation analysis has been performed on the resulting numerical gene expression profiles for each stage. Based on the correlated clusters of spatial gene expression and detailed descriptions of gene expression domains, various mechanisms for developmental gene expression are proposed. RESULTS: In the blastula and gastrula stages of development in N. vectensis, its continuous sheet of cells is partitioned into correlating gene expression domains. During progressing development, these regions likely correspond to different fates. A statistical analysis shows that genes generally remain expressed during the planula stages in those major regions that they occupy at the end of gastrulation. DISCUSSION: Observed shifts in gene expression domain boundaries suggest that elongation in the planula stage mainly occurs in the vegetal ring under the influence of the gene Rx. The secondary body axis in N. vectensis is proposed to be determined at the mid blastula transition. CONCLUSIONS: Early gene expression domains in N. vectensis appear to maintain a positional order along the primary body axis. Early determination in N. vectensis occurs in two stages: expression in broad circles and rings in the blastula is consolidated during gastrulation, and more complex expression patterns appear in the planula within these broad regions. Quantification and comparison of gene expression patterns across a database can generate hypotheses about collective cell movements before these movements are measured directly.

What games support the evolution of an ingroup bias?

There is an increasing wealth of models trying to explain the evolution of group discrimination and an ingroup bias. This paper sets out to systematically investigate the most fundamental assumption in these models: in what kind of situations do the interactions take place? What strategic structures - games - support the evolution of an ingroup bias? More specifically, the aim here is to find the prerequisites for when a bias also with respect to minimal groups - arbitrarily defined groups void of group-specific qualities - is selected for, and which cannot be ascribed to kin selection. Through analyses and simulations of minimal models of two-person games, this paper indicates that only some games are conducive to the evolution of ingroup favouritism. In particular, this class does not contain the prisoners׳ dilemma, but it does contain anti-co-ordination and co-ordination games. Contrasting to the prisoners׳ dilemma, these are games where it is not a matter of whether to behave altruistically, but rather one of predicting what the other person will be doing, and where I would benefit from you knowing my intentions. In anti-co-ordination games, on average, not only will agents discriminate between groups, but also in such a way that their choices maximise the sum of the available payoffs towards the ingroup more often than towards the outgroup. And in co-ordination games, even if agents do manage to co-ordinate with the whole population, they are more likely to co-ordinate on the socially optimal equilibrium within their group. Simulations show that this occurs most often in games where there is a component of risk-taking, and thus trust, involved. A typical such game is the stag hunt or assurance game.

The cultural evolution of democracy: saltational changes in a political regime landscape.

Transitions to democracy are most often considered the outcome of historical modernization processes. Socio-economic changes, such as increases in per capita GNP, education levels, urbanization and communication, have traditionally been found to be correlates or 'requisites' of democratic reform. However, transition times and the number of reform steps have not been studied comprehensively. Here we show that historically, transitions to democracy have mainly occurred through rapid leaps rather than slow and incremental transition steps, with a median time from autocracy to democracy of 2.4 years, and overnight in the reverse direction. Our results show that autocracy and democracy have acted as peaks in an evolutionary landscape of possible modes of institutional arrangements. Only scarcely have there been slow incremental transitions. We discuss our results in relation to the application of phylogenetic comparative methods in cultural evolution and point out that the evolving unit in this system is the institutional arrangement, not the individual country which is instead better regarded as the 'host' for the political system.