  In the present work we extend the Bak-Sneppen model for biological evolution
by introducing local interactions between species. This ``environmental''
perturbation can modify the intrinsic fitness of each element of the ecology,
leading to higher survival probability, even for the less fit. While the system
still self-organizes toward a critical state, the distribution of fitness
broadens, losing the classical step-function shape. A possible application in
economics is discussed, where firms are represented like evolving species
linked by mutual interests.
