Since the origin of life, metabolic networks provide cells with nutrition and energy. Modern networks require thousands of enzymes that perform catalysis. Such networks must have arisen from simpler precursors. Investigating the metabolism of modern cells, Xavier et al. have identified ancient and conserved autocatalytic networks at the core of microbial metabolism that require only cofactors and metals as catalysts. These networks are simpler and less complete than modern metabolism, but they can grow, they generate the building blocks of protein and RNA, and they trace to the common ancestor of all life. The paper was published in Proceedings of the Royal Society B on March 11th.