Simulating Bak-Sneppen model[1]. Each bar denotes a species fitness. A species having the minimal fitness is removed together with its neighboring species. They are replaced by new species having fitnesses randomly drawn from the uniform distribution.
The system evolves to a self-organized critical (SOC) state, where scale-free avalanches of extinctions occur. Wikipedia
[1] Bak, P.; Kim Sneppen (1993). "Punctuated equilibrium and criticality in a simple model of evolution". Physical Review Letters. 71 (24): 4083–4086.