CONCEPT
Bak-Sneppen Model
A minimal evolutionary model demonstrating that species extinctions follow power-law distributions when ecosystems self-organize to criticality — reproducing punctuated equilibrium without external catastrophes.
The Bak-Sneppen model, published in 1993, extended self-organized criticality from physical systems to biological evolution. In the model, species are arranged in a line, each assigned a random fitness value. At each time step, the least-fit species is replaced along with its immediate neighbors, representing the ecological perturbation that one species' extinction imposes on its environment. New fitness values are assigned randomly. The model self-organizes to a critical state where species replacements trigger cascading extinctions following a power-law distribution. Most 'extinctions' are small (a few species), some are medium, rare ones are enormous (sweeping across the ecosystem). The model reproduced the statistical signature of the fossil record — long periods of stasis punctuated by rapid reorganization — without requiring asteroid impacts or volcanic eruptions. Extinctions are avalanches in a critical evolutionary system.
In The You On AI Field Guide
The Bak-Sneppen model was Bak's response to the debate between gradualists and punctuationists in evolutionary biology. Niles Eldredge and Stephen Jay Gould had argued in 1972 that the fossil record showed punctuated equilibrium