
Gavrilets applied the “Page 99 Test” to his latest book, Social Influence and the Logic of Collective Action, and shared the following:
Page 99 falls in the chapter “Dynamics of Social Influence.” It begins with a figure showing adoption curves in the classic Bass model of innovation diffusion, which combines influence from external authorities with influence from peers. The page emphasizes that “even a relatively weak effect of external influence ... can significantly speed up the spread of the innovation.” It then notes how the model can incorporate individual differences and network interactions before turning to the classic Daley-Kendall model of rumor spread, which adapts ideas from epidemic models.Visit Sergey Gavrilets's website.
The Page 99 Test works reasonably well for my book, although it works better as a sample of the book’s approach than as a summary of its full argument. The page captures one of its central concerns: how individual behavior spreads through a population under the combined influence of authorities and peers. It also illustrates the book’s typical strategy: begin with a simple formal model, explain its intuition, visualize its consequences, and then connect it to related models and possible extensions.
At the same time, a browser reading only this page might conclude that the book is mainly about the diffusion of innovations and rumors. Its larger subject is collective action: why groups sometimes solve shared problems and sometimes fail, even when cooperation would benefit everyone. The book asks who contributes and who free-rides, why people punish violators or follow leaders, how norms emerge and change, and when small behavioral shifts can produce large social transformations.
My central argument is that no single mechanism can adequately explain collective action. Material incentives matter, but so do personal attitudes and moral values, beliefs about what others will do, social norms, peer influence, cultural authorities, cognition, learning, and individual differences. The book brings insights from game theory, behavioral economics, evolutionary theory, psychology, and cultural evolution into a common framework. This framework shows how actions, attitudes, and beliefs can coevolve and reinforce one another, sustaining cooperation but also trapping groups in persistent collective failure. It also helps identify tipping points, explain why apparently ineffective institutions endure, and clarify when interventions by leaders, authorities, or committed minorities can redirect a group’s trajectory.
Page 99 therefore reveals an important engine of the book - social influence operating through nonlinear population dynamics - but not the full machine. It gives a good taste of how the book thinks, but only a partial map of what it explains.
--Marshal Zeringue






















