About

Hi! I’m Julien. I am a postdoctoral researcher based in Paris and will join the SMILE team at École normale supérieure in September 2026. I also co-lead a project funded by PSL’s TERRAE program that applies my theoretical work on cooperation to the design of policies supporting more sustainable household energy use.

I study the psychology of large-scale cooperation: how human minds navigate and build the rules, norms, and institutions that make societies possible.

Humans cooperate with strangers on a scale no other species approaches. From an evolutionary perspective, this is puzzling because reputation—the central mechanism sustaining cooperation between strangers—reaches only as far as reliable information about people’s behavior can travel.

I study rules, norms, roles, and institutions as social technologies. They cannot eliminate conflicts of interest, but they can redesign cooperation problems by defining which behaviors count as acceptable and changing how reputational incentives are distributed.

Using evolutionary game theory, I show how rigid rules can protect cooperation by closing loopholes; how specialized roles can concentrate responsibility and reputational stakes on a visible few; and how institutions can turn difficult cooperation problems into simpler ones that reputation can sustain. I also use experiments and computational models to study how people decide which rules should govern cooperation.

I completed my PhD in cognitive science at École normale supérieure and Télécom Paris, then held research appointments at the Max Planck Institute for Evolutionary Biology, the University of Guelph, and MIT. Here’s a recent CV.