Social roles are neither predetermined nor set in stone

In animal societies as in human ones, some individuals regularly produce resources while others appropriate them. Contrary to what evolutionary theories¹ had previously suggested, these social roles do not depend solely on innate individual predispositions. On the contrary, a study in mice conducted by scientists from CNRS² and Sorbonne Université shows that the distribution and stabilisation of these roles within groups arise from a collective dynamic shaped by random early interactions and by learning. Social roles are therefore not set in stone, but dynamic and highly flexible, allowing each individual to switch roles when the system in which it operates changes. These findings, due to be published in Nature on 1 April, are based on an analysis of the roles taken on by mice in a semi-natural environment in which food can be obtained by pressing a lever.

By distinguishing between individuals displaying “producer” behaviour, producing more than they consume; “scrounger” behaviour, consuming more than they produce; and “storer” behaviour, pressing the lever frequently but delaying food retrieval, the research team made the unexpected finding that, in the mouse groups studied, the distribution of social roles is driven by different dynamics in male and female groups. Whereas a division of labour based on competition emerges in male groups, female groups, by contrast, remain remarkably homogeneous, with no specialisation taking hold: each individual behaves in much the same way, without attempting to exploit the resources produced by its peers. However, introducing a single male into a group of females may be enough to shift them towards competitive behaviour.

At the brain level, the scientists observed that dopamine is involved in the stabilisation of social roles: a surge in dopamine activity, which is involved in reward-based learning,³ is recorded in “producer” individuals when they themselves press the lever that provides access to food, whereas in “scroungers” this surge occurs when another individual uses that same lever. Dopamine does not determine which social role individuals adopt, but it is the mechanism through which group dynamics reinforce a role initially set in motion by the experience of early interactions.

Notes

1. Evolutionary theories have long viewed this phenomenon as a stable equilibrium between strategies, which can give the impression that roles are predefined.

2. Working at the Brain Plasticity laboratory (CNRS/ESPCI Paris – PSL) and the Institut des Systèmes Intelligents et de Robotique (ISIR) (CNRS/Sorbonne Université), as well as at the Institut de Génomique Fonctionnelle (CNRS/Inserm/University of Montpellier) and the Human Genetics and Cognitive Functions laboratory (CNRS/Institut Pasteur).

3. Dopamine does not directly trigger happiness but plays a role in reward anticipation.