We propose an alternative to the Bak-Sneppen model for species co-evolution. In our model the closest neighbors of the least adapted species are replaced by new species with a certain probability α. The probability α can be regarded as the interaction strength between nearest species. We show that the system can always self-organizes to a critical state when the interaction strength α is larger than zero. The critical exponents of our model are estimated through the finite size scaling analysis, and found to be the same as those of the origi...
