Using portraits to quantify the changes of generalized social trust in European history: A replication study.

A portrait is an exercise of impression management: the sitter can choose the impression she or he wants to create in the eyes of others': competence, trustworthiness, dominance, etc. Indirectly, this choice informs us about the qualities that were specifically valued at the time the portrait was created. In a previous paper, we have shown that cues of perceived trustworthiness in portraits increased in time during the modern period in Europe, meaning that people probably granted more importance to be seen as a trustworthy person. Moreover, this increase is correlated to economic development. In this study, we aim to replicate this result, using more controlled databases: 1) a newly created database of European head-of-state sovereigns (N = 966, from 1400 to 2020), that is a database of individuals holding the same social position across time and countries, and 2) a database of very high-quality portraits digitized with the same technique, and coming from the same Museum, the Chateau de Versailles database (N = 2,291, from 1483 to 1938). Using mixed effects linear models, we observed in the first dataset that the modeled perceived facial trustworthiness of these sovereigns' faces increased over time (b = 0.182 ± 0.04 s.e.m., t(201) = 4.40, p < 0.001). On the opposite, no effect of time was detected on the portraits of the Château de Versailles (b = - 0.02 ± 0.03 s.e.m., t(759) = - 0.85, p > .250). We conclude by discussing the potential of this new technique to uncover long-term behavioral changes in history, as well as its limitations.

Quantifying the scientific revolution.

The Scientific Revolution represents a turning point in the history of humanity. Yet it remains ill-understood, partly because of a lack of quantification. Here, we leverage large datasets of individual biographies (N = 22,943) and present the first estimates of scientific production during the late medieval and early modern period (1300-1850). Our data reveal striking differences across countries, with England and the United Provinces being much more creative than other countries, suggesting that economic development has been key in generating the Scientific Revolution. In line with recent results in behavioural sciences, we show that scientific creativity and economic development are associated with other kinds of creative activities in philosophy, literature, music and the arts, as well as with inclusive institutions and ascetic religiosity, suggesting a common underlying mindset associated with long-term orientation and exploration. Finally, we investigate the interplay between economic development and cultural transmission (the so-called 'Republic of Letters') using partially observed Markov models imported from population biology. Surprisingly, the role of horizontal transmission (from one country to another) seems to have been marginal. Beyond the case of science, our results suggest that economic development is an important factor in the evolution of aspects of human culture.

The cultural evolution of love in literary history.

Since the late nineteenth century, cultural historians have noted that the importance of love increased during the Medieval and Early Modern European period (a phenomenon that was once referred to as the emergence of 'courtly love'). However, more recent works have shown a similar increase in Chinese, Arabic, Persian, Indian and Japanese cultures. Why such a convergent evolution in very different cultures? Using qualitative and quantitative approaches, we leverage literary history and build a database of ancient literary fiction for 19 geographical areas and 77 historical periods covering 3,800 years, from the Middle Bronze Age to the Early Modern period. We first confirm that romantic elements have increased in Eurasian literary fiction over the past millennium, and that similar increases also occurred earlier, in Ancient Greece, Rome and Classical India. We then explore the ecological determinants of this increase. Consistent with hypotheses from cultural history and behavioural ecology, we show that a higher level of economic development is strongly associated with a greater incidence of love in narrative fiction (our proxy for the importance of love in a culture). To further test the causal role of economic development, we used a difference-in-difference method that exploits exogenous regional variations in economic development resulting from the adoption of the heavy plough in medieval Europe. Finally, we used probabilistic generative models to reconstruct the latent evolution of love and to assess the respective role of cultural diffusion and economic development.

The rise of prosociality in fiction preceded democratic revolutions in Early Modern Europe.

The English and French Revolutions represent a turning point in history, marking the beginning of the modern rise of democracy. Recent advances in cultural evolution have put forward the idea that the early modern revolutions may be the product of a long-term psychological shift, from hierarchical and dominance-based interactions to democratic and trust-based relationships. In this study, we tested this hypothesis by analyzing theater plays during the early modern period in England and France. We found an increase in cooperation-related words over time relative to dominance-related words in both countries. Furthermore, we found that the accelerated rise of cooperation-related words preceded both the English Civil War (1642) and the French Revolution (1789). Finally, we found that rising per capita gross domestic product (GDPpc) generally led to an increase in cooperation-related words. These results highlight the likely role of long-term psychological and economic changes in explaining the rise of early modern democracies.

Tracking historical changes in trustworthiness using machine learning analyses of facial cues in paintings.

Social trust is linked to a host of positive societal outcomes, including improved economic performance, lower crime rates and more inclusive institutions. Yet, the origins of trust remain elusive, partly because social trust is difficult to document in time. Building on recent advances in social cognition, we design an algorithm to automatically generate trustworthiness evaluations for the facial action units (smile, eye brows, etc.) of European portraits in large historical databases. Our results show that trustworthiness in portraits increased over the period 1500-2000 paralleling the decline of interpersonal violence and the rise of democratic values observed in Western Europe. Further analyses suggest that this rise of trustworthiness displays is associated with increased living standards.

Why cooperation is not running away.

A growing number of experimental and theoretical studies show the importance of partner choice as a mechanism to promote the evolution of cooperation, especially in humans. In this paper, we focus on the question of the precise quantitative level of cooperation that should evolve under this mechanism. When individuals compete to be chosen by others, their level of investment in cooperation evolves towards higher values, a process called competitive altruism, or runaway cooperation. Using a classic adaptive dynamics model, we first show that when the cost of changing partner is low, this runaway process can lead to a profitless escalation of cooperation. In the extreme, when partner choice is entirely frictionless, cooperation even increases up to a level where its cost entirely cancels out its benefit. That is, at evolutionary equilibrium, individuals gain the same payoff than if they had not cooperated at all. Second, importing models from matching theory in economics we, however, show that when individuals can plastically modulate their choosiness in function of their own cooperation level, partner choice stops being a runaway competition to outbid others and becomes a competition to form the most optimal partnerships. In this case, when the cost of changing partner tends towards zero, partner choice leads to the evolution of the socially optimum level of cooperation. This last result could explain the observation that human cooperation seems to be often constrained by considerations of social efficiency.

Fairness, more than any other cognitive mechanism, is what explains the content of folk-economic beliefs.

We applaud Boyer & Petersen's (B&P's) article on economic folk beliefs. We believe that it is crucial for the future of democracy to identify the cognitive systems through which people form their beliefs about the working of the economy. In this commentary, we put forward the idea that, although many systems are involved, fairness is probably the main driver of folk-economic beliefs.

Correction: On the evolutionary origins of equity.

[This corrects the article DOI: 10.1371/journal.pone.0173636.].

On the evolutionary origins of equity.

Equity, defined as reward according to contribution, is considered a central aspect of human fairness in both philosophical debates and scientific research. Despite large amounts of research on the evolutionary origins of fairness, the evolutionary rationale behind equity is still unknown. Here, we investigate how equity can be understood in the context of the cooperative environment in which humans evolved. We model a population of individuals who cooperate to produce and divide a resource, and choose their cooperative partners based on how they are willing to divide the resource. Agent-based simulations, an analytical model, and extended simulations using neural networks provide converging evidence that equity is the best evolutionary strategy in such an environment: individuals maximize their fitness by dividing benefits in proportion to their own and their partners' relative contribution. The need to be chosen as a cooperative partner thus creates a selection pressure strong enough to explain the evolution of preferences for equity. We discuss the limitations of our model, the discrepancies between its predictions and empirical data, and how interindividual and intercultural variability fit within this framework.

Both collection risk and waiting costs give rise to the behavioral constellation of deprivation.

Pepper & Nettle explain the behavioral constellation of deprivation (BCD) in terms of differences in collection risk (i.e., the probability of collecting a reward after some delay) between high- and low-socioeconomic-status (SES) populations. We argue that a proper explanation should also include the costs of waiting per se, which are paid even when the benefits are guaranteed.

The nature and dynamics of world religions: a life-history approach.

In contrast with tribal and archaic religions, world religions are characterized by a unique emphasis on extended prosociality, restricted sociosexuality, delayed gratification and the belief that these specific behaviours are sanctioned by some kind of supernatural justice. Here, we draw on recent advances in life history theory to explain this pattern of seemingly unrelated features. Life history theory examines how organisms adaptively allocate resources in the face of trade-offs between different life-goals (e.g. growth versus reproduction, exploitation versus exploration). In particular, recent studies have shown that individuals, including humans, adjust their life strategy to the environment through phenotypic plasticity: in a harsh environment, organisms tend to adopt a 'fast' strategy, pursuing smaller but more certain benefits, while in more affluent environments, organisms tend to develop a 'slow' strategy, aiming for larger but less certain benefits. Reviewing a range of recent research, we show that world religions are associated with a form of 'slow' strategy. This framework explains both the promotion of 'slow' behaviours such as altruism, self-regulation and monogamy in modern world religions, and the condemnation of 'fast' behaviours such as selfishness, conspicuous sexuality and materialism. This ecological approach also explains the diffusion pattern of world religions: why they emerged late in human history (500-300 BCE), why they are currently in decline in the most affluent societies and why they persist in some places despite this overall decline.

Preschoolers' understanding of merit in two Asian societies.

Recent research in moral psychology have suggested that children make judgments about distributive justice early on in development, and in particular they appear to be able to use merit when distributing the benefits of a collective action. This prediction has recently been validated in various western cultures but it is unknown whether it also applies to more collectivistic cultures, in which the group might be favoured over the individual, and need over merit. Here, we investigate merit-based distributions among 81 children belonging to two Asian societies, China and Japan (mean age = 5.0 years). In line with the idea that children's moral psychology develops early, we found that Chinese and Japanese children are able to use merit to distribute the benefits of a collective action.

Increased affluence explains the emergence of ascetic wisdoms and moralizing religions.

BACKGROUND: Between roughly 500 BCE and 300 BCE, three distinct regions, the Yangtze and Yellow River Valleys, the Eastern Mediterranean, and the Ganges Valley, saw the emergence of highly similar religious traditions with an unprecedented emphasis on self-discipline and asceticism and with "otherworldly," often moralizing, doctrines, including Buddhism, Jainism, Brahmanism, Daoism, Second Temple Judaism, and Stoicism, with later offshoots, such as Christianity, Manichaeism, and Islam. This cultural convergence, often called the "Axial Age," presents a puzzle: why did this emerge at the same time as distinct moralizing religions, with highly similar features in different civilizations? The puzzle may be solved by quantitative historical evidence that demonstrates an exceptional uptake in energy capture (a proxy for general prosperity) just before the Axial Age in these three regions. RESULTS: Statistical modeling confirms that economic development, not political complexity or population size, accounts for the timing of the Axial Age. CONCLUSIONS: We discussed several possible causal pathways, including the development of literacy and urban life, and put forward the idea, inspired by life history theory, that absolute affluence would have impacted human motivation and reward systems, nudging people away from short-term strategies (resource acquisition and coercive interactions) and promoting long-term strategies (self-control techniques and cooperative interactions).

Preschoolers are able to take merit into account when distributing goods.

Classic studies in developmental psychology demonstrate a relatively late development of equity, with children as old as 6 or even 8-10 years failing to follow the logic of merit--that is, giving more to those who contributed more. Following Piaget (1932), these studies have been taken to indicate that judgments of justice develop slowly and follow a stagelike progression, starting off with simple rules (e.g., equality: everyone receives the same) and only later on in development evolving into more complex ones (e.g., equity: distributions match contributions). Here, we report 2 experiments with 3- and 4-year-old children (N = 195) that contradict this constructivist account. Our results demonstrate that children as young as 3 years old are able to take merit into account by distributing tokens according to individual contributions but that this ability may be hidden by a preference for equality.