Andreas Wagner

Paper #: 02-08-040

The number of interactions per node in metabolic network graphs follows a power law. I discuss two possible evolutionary explanations of this feature. The first relates to the observation that graphs with this degree distribution are robust to random node removal. This observation has lead to the hypothesis that metabolic networks show power-law degree distributions because it endows them with robustness against perturbations. However, abiotic chemical reaction networks also show this degree distribution, which makes robustness a less likely candidate cause of this distribution in metabolism. Secondly, this power-law distribution may be the result of the growth of metabolism through addition of metabolites over billions of years. A variety of graph-growth models that lead to similarly structured graphs predicts that highly connected network nodes are old nodes. Empirical evidence supports this prediction for metabolic networks.