The paper by Ravasz et al. explores the hierarchical organization of metabolic networks, highlighting the coexistence of modularity and scale-free topology. They analyze metabolic networks from 43 different organisms and find that these networks are characterized by a high clustering coefficient, suggesting inherent modularity, despite their scale-free degree distribution. To resolve this contradiction, they propose a "hierarchical" network model, which combines a scale-free topology with embedded modularity. This model consists of small, densely interconnected modules that group into larger, less cohesive units, forming a hierarchical structure. The hierarchical organization is quantitatively supported by the power-law scaling of the clustering coefficient, \( C(k) \sim k^{-1} \), where \( k \) is the degree of a node. The authors demonstrate that this hierarchical modularity is evident in the metabolic network of *Escherichia coli*, where functional modules are well-correlated with topological modules. This hierarchical structure may reflect the true functional organization of cellular metabolism and could have implications for understanding the evolutionary mechanisms underlying the emergence of metabolic networks.The paper by Ravasz et al. explores the hierarchical organization of metabolic networks, highlighting the coexistence of modularity and scale-free topology. They analyze metabolic networks from 43 different organisms and find that these networks are characterized by a high clustering coefficient, suggesting inherent modularity, despite their scale-free degree distribution. To resolve this contradiction, they propose a "hierarchical" network model, which combines a scale-free topology with embedded modularity. This model consists of small, densely interconnected modules that group into larger, less cohesive units, forming a hierarchical structure. The hierarchical organization is quantitatively supported by the power-law scaling of the clustering coefficient, \( C(k) \sim k^{-1} \), where \( k \) is the degree of a node. The authors demonstrate that this hierarchical modularity is evident in the metabolic network of *Escherichia coli*, where functional modules are well-correlated with topological modules. This hierarchical structure may reflect the true functional organization of cellular metabolism and could have implications for understanding the evolutionary mechanisms underlying the emergence of metabolic networks.