Figure 1.

The equilibrium points of a nonlinear biological network in a phenotypic landscape. The nonlinear stochastic biological network has many local equilibrium points (phenotypic traits). The phenotypic landscape of three stable equilibrium points with a vertical scale illustrating the relative network robustness of the equilibrium points (phenotypic traits) of the nonlinear stochastic biological network in evolution, ie, the equilibrium point at x_e with deeper and wider basin, is more robust. Here, x_e is the equilibrium point (phenotypic trait) of interest by natural selection.