Some theoretical examples of possibilities for natural selection in a prebiotic organic medium at the molecular level are given. These examples, presented in the form of simple kinetic models, are based on the idea that the occurrence of autocatalysis and self-duplication broke through the limitations imposed by contacts by chance with rare but essential molecules in the surrounding medium. It is shown that many regulatory mechanisms and the development of organization are logical consequences of this selection process. Symbiogenetic associations might (...) play a role in producing more efficiently duplicating systems. The peculiar circumstances prevailing during pre-biological evolution, including the chance of irregular duplications and the possibilities for the uptake of systems from the surrounding medium, suggest the accumulation in this phase of evolution of a vast amount of genetic information whose potentialities became manifest during the subsequent biological evolution. (shrink)