Before revision:  The model cell includes three independent  pathways, whose topologies of PPI subnetworks are different, but whose functional concentrations equally contribute to cell's fitness . The model cells evolve through genotypic mutations and phenotypic protein copy number variations.
After revision:  The model cell includes three independent pathways, whose topologies of PPI subnetworks are different, but whose contributions to the cell fitness are equal. Model cells evolve through genotypic mutations and phenotypic protein copy number variations.