Extremal dynamics model evolving networks

We investigate an extremal dynamics model of evolution,with! variable numbe r of units. Because of addition and removal of the units, the topology of t he:network evolves and the network splits into several clusters. The activi ty is mostly concentrated in the largest cluster. The time dependence of th e number of units exhibits intermittent structure. The self-organized criti cality is manifested by a power-law: distribution of forward avalanches, bu r two regimes with:distinct exponents tau = 1.98 +/- 0.04 and tau(')= 1.65 +/- 0.05 are found. The distribution of extinction;sizes obeys a power law with exponent 2.32 +/- 0.05.