  Interaction strength is introduced in a model of evolution in d-dimension
space. It is realized by imposing a constraint concerning 2d differences of
fitnesses between that of any extremal site and those of its 2d nearest
neighbours at each time step in the evolution of the model. For any given
interaction strength between 0 and 1 the model can self-organize to a critical
state. Two exact equations found in Bak-Sneppen model still hold in our model
for different interaction strength. Simulations of one- and two-dimensional
models for ten different values of interaction are given. It is found that
self-organized threshold decreases with interaction strength increasing. It is
also shown that the critical exponent, and two basic exponents, avalanche
distribution, and avalanche dimension, are interaction strength dependent.
