Many biologists today recoil at the notion of an organism without genetically functional nucleic acids. True, such an organism would be more efficient if it had genes. And genes would have to emerge before such a living microsphere could transform into cells as we know them today. However, it might just be that such a system would provide the possibility for the spontaneous formation of uninformed nucleic acids and their transition to informed ones. Let us speculate further on how that might occur.
Because these early organisms or protocells could be termed living, they would also be evolvable. That means natural selection would act on their variations and preserve the more advantageous ones. What would be the nature of such selection pressures? This can be made clearer by looking at a basic reality faced by all organisms. If a species is going to persist, the individual organism must survive long enough to form more of itself. Some rocks and other tough substances persist simply because they are durable. Organisms, by comparison, are not durable. In fact, they are comparatively delicate, but organisms that persist do so because they reproduce faster than they are destroyed. If we indicate the average period of duration of an individual as the survival interval, and the average period needed to form more of itself as the formative interval, then, for persistence, the survival interval must be greater than the formative interval. Therefore, selection will favor anything that increases the survival interval or decreases the formative interval. These selection pressures are unavoidably present; they arose with the first living thing and have been the basic reality of survival down to the present, and will continue to be.
What increases the survival period of the protocell? There are at least three conditions that increase survival: (1) an improved selective uptake of substances from the environment, (2) an increased concentration of reactants needed for the life of the protocell, and (3) stabilized functional (enzymatic) and structural (membranes, in particular) proteins. All three are, of course, interrelated. What decreases the formative period? Two points deserve emphasis: (1) speeded up reactions needed for the life of the cell, which can be the result of increasing the concentration of reactants and improving the efficiency of enzymes, and (2) proper distribution of functional and structural components.