Belief in conspiracy theories—such as that the 9/11 terrorist attacks were an inside job or that the pharmaceutical

industry deliberately spreads diseases—is a widespread and culturally universal phenomenon. Why do so many

people around the globe believe conspiracy theories, and why are they so influential? Previous research focused on

the proximate mechanisms underlying conspiracy beliefs but ignored the distal, evolutionary origins and functions.

We review evidence pertaining to two competing evolutionary hypotheses: (a) conspiracy beliefs are a by-product

of a suite of psychological mechanisms (e.g., pattern recognition, agency detection, threat management, alliance

detection) that evolved for different reasons, or (b) conspiracy beliefs are part of an evolved psychological mechanism

specifically aimed at detecting dangerous coalitions. This latter perspective assumes that conspiracy theories are

activated after specific coalition cues, which produce functional counterstrategies to cope with suspected conspiracies.

Insights from social, cultural and evolutionary psychology provide tentative support for six propositions that follow

from the adaptation hypothesis. We propose that people possess a functionally integrated mental system to detect

conspiracies that in all likelihood has been shaped in an ancestral human environment in which hostile coalitions—

that is, conspiracies that truly existed—were a frequent cause of misery, death, and reproductive loss.