A universal power law and proportionate change process characterize the evolution of metabolic networks S. Singh, A. Samal, V. Giri, S. Krishna, N. Raghuram and S. Jain Eur. Phys. J. B, 57 1 (2007) 75-80 Published online: 23 May 2007 DOI: 10.1140/epjb/e2007-00145-0