Clever vermin? Collective intelligence in rats and roaches

Collective intelligence (CI) is the capacity of groups to outperform individuals in tasks such as decision-making, coordination and problem-solving. A significant challenge to studying CI is that it encompasses a wide variety of behaviours that are underpinned by different mechanisms. To balance inclusivity with conceptual clarity, we propose a typology of CI mechanisms including self-organized coordination, distributed decision-making, cooperative problem-solving, statistical aggregation and culture and cultural improvement. This typology helps clarify the minimum requirements for CI and how other, more cognitive complex mechanisms may have layered on top of these. As model comparative species, we focus on two ecologically successful generalists, rats (Rattus) and cockroaches (Blattodea). Cockroaches show evidence of collective behaviours, but these rely on a more ancestral set of mechanisms that lack cognitive complexity. Conversely, rats share important ecological traits with cockroaches but exhibit social traits found in primates, including cultural learning, distributed decision-making, empathy and cooperation. This comparison can show how similar collective outcomes can emerge even with disparate mechanisms and provide a way to uncover evolutionary design principles of CI. Ultimately, we can use such comparisons to determine which features of CI are universal properties of collectives and which are contingent on specific cognitive adaptations. This article is part of the theme issue 'The evolution of collective intelligence'.