The second school, aiming for a bottom-up strategy, proposes that the first entities conforming to life's definition could have been much simpler . Its supporters posit that life began with spatially demarcated assemblages of small organic molecules, not necessarily resembling those of present life organic repertoire. At the heart of this scenario is the assumption that the assemblies would build up mutually catalytic networks, whose function rests on simple organocatalysts . Under certain quantitatively defined kinetic constraints, similar to those that govern present-day metabolism, such multimolecular networks would reproduce and evolve . The simplicity of the proposed route renders it a parsimonious path to reproduction, whereby more complex, life-like RNA-based entities would subsequently arise by lengthy Darwinian evolution . It has been argued that this bottom-up approach can foresee the development of simple, and then more complex catalytic networks, plausibly bridging between prebiotic chemical sludge and protolife .