Institut Jean Nicod

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Soutenance de thèse - Léonard Guillou - "Explaining the variability of trust across time, space and social classes : A behavioral ecology approach"


Date : Mardi 16 novembre à 14h

Lieu : ENS, salle Favard, 46 rue d’Ulm, 75005 Paris (contacter Léonard Guillou pour pouvoir y assister)

Jury :

  • Jeanne, BOVET, MCF, Northumbria University : Rapportrice 
  • Pascal, BOYER, PU, Washington University in St. Louis : Rapporteur
  • Julie, GRÈZES, DR, ENS : Examinatrice
  • Michel, RAYMOND, DR, CNRS : Examinateur
  • Lou, SAFRA, MCF, Sciences Po : Co-encadrante
  • Nicolas, BAUMARD, DR, École normale supérieure : Directeur de thèse


Résumé :

Social or interpersonal trust is the belief that people are on average trustworthy, that they cooperate in good faith, without trying to cheat and exploit others. Among other things, it allows unrelated individuals, who may not have aligned interests, to cooperate. It therefore has many benefits at both the individual and societal levels. However, despite its undeniable advantages, social trust is highly variable not only between countries but also between individuals. How can this variability be explained ? In this thesis, I explore the idea that some of the variability in interpersonal trust can be explained by differences in resource levels. From an evolutionary perspective, social trust does indeed come with several risks and costs. One of these risks is that of mistaking a "cheater" for a trustworthy partner. In this situation, the cheater may exploit you without benefit to you. If your resources are low, the cost of this cheating is more salient than if they are abundant. It is therefore not optimal to have a very high level of social trust when you have low resources. In my thesis, I first investigated how the level of resources might impact social trust. I tested the hypothesis that it is temporal preferences that mediate the relationship between resource level and social trust (Chapter 2). In other words, part of the positive effect of the level of resources on social trust is due to the fact that higher resources lead to a more long-term orientation. Social trust, because of its direct link to reciprocal cooperation, is itself a long-term oriented trait. This partly explains how economic resources can influence the level of social trust of individuals. I then turn to the variability of trust over history. Despite terrible persisting inequalities, human societies have become much richer over time, especially since the beginning of the industrial revolution. Would it then be possible to observe variations in the levels of social trust over time ? To answer this question, I have relied on what has come down to us from people who lived in the past and which is a product of their psychology : cultural items. These cultural items can be considered as "cognitive fossils", a kind of partial imprint of their psychology at that time. More precisely, I was interested in facial representations, to what extent photographs or painted portraits represent faces that inspire confidence or not (Chapters 3, 4 and 5). I showed that for most of the datasets collected, the level of perceived trust in faces increased over time and that this increase was well explained by economic variations. Considering these analyses, there is good reason to believe that the changes in trust-related attitudes that have occurred in the past and are likely to occur in the future are, at least in part, determined by environmental changes, foremost among which is the level of resources of individuals. À noter : la soutenance sera en français.