Fig. 1.

Simulations of the linear fitness model with Δt=0.1, ϵ=10⁻³, η=10⁻³ and n_min=n_max/10. The instantaneous distributions of the populations over the species index normalized by n_max as a function of time are shown for n_max=10⁴ (A) and n_max=10⁵ (B). Wave-like behavior is evident in both cases, though the smaller population leads to a noisier and slower wave. Panels (C) and (D) show the corresponding probabilities averaged over 800 realizations. The wave velocity, by a least squares linear fit to the ensemble mean fitness, is 0.93×10⁻³ and 2.1×10⁻³ indices per unit time for (C) and (D), respectively.