Generic criticality in a model of evolution

Using Monte Carlo simulations, we show that for a certain model of biological evolution, which is driven by nonextremal dynamics, active and absorbing phases are separated by a critical phase. In this phase both the density of active sites rho(t) and the survival probability of spreading P(t) decay as t(-delta), where delta approximately 0.5. At the critical point that separates the active and critical phases delta approximately 0.29, which suggests that this point belongs to the so-called parity-conserving universality class. Such a classification is also supported by finite-size analysis. The model has infinitely many absorbing states and, except for a single point, has no apparent conservation law.