In Cooperation as a Law of Nature, Boris Kriger traces a single explosive idea from the Siberian wilderness of the nineteenth century to the frontiers of modern science: mutual aid is not a moral achievement. It is a dynamical default—what remains when you stop interfering. Drawing on Peter Kropotkin’s revolutionary biology, contemporary neurochemistry, network theory, information science, and nine years of running a shelter where the only rule was “no one tells anyone what to do,” Kriger constructs a case that cooperation is not fragile, not idealistic, and not optional. It is the way complex systems naturally behave when external perturbation is removed.