Self-Organized Criticality, Optimization and Biodiversity
  By driven to extinction species less or poorly adapted, the Darwinian evolutionary theory is intrinsically an optimization theory. We investigate two optimization algorithms with such evolutionary characteristics: the Bak-Sneppen and the Extremal Optimization. By comparing their mean fitness in the steady state regime, we conclude that the Bak-Sneppen dynamics is more efficient than the Extremal Optimization if the parameter $\tau$ is in the interval $[0,0.86]$. The determination of the spatial correlation and the probability distribution of the avalanches show that the Extremal Optimization dynamics does not lead the system into a critical self-organized state. Trough a discrete form of the Bak-Sneppen model we argument that biodiversity is an essential requisite to preserve the self-organized criticality. 
Roberto N. Onody, Paulo A. de Castro