 If modern biological systems evolved from molecules that did not have the ability to reproduce, let alone replicate, one might ask: what is the simplest case of evolution by natural selection? It is a case in which different types of entities have different persistences but do not produce any offspring. In this model, the types with the property of persisting longer represent an increasing frequency of the total population over time. One problem, though in a model of persistence alone, is that each time one entity goes out of existence, it is not replaced by another entity; thus, over time, the population size tends towards zero. Although this does not mean that evolution by natural selection cannot occur in such populations, this places important constraints on the evolutionary dynamics of this population (Van Valen 1989). Further, it is possible to regard the ability for a population to maintain its size or increase its size as a primordial form of adaptation. This idea casts some doubt on the view that paradigmatic cases of evolution by natural selection require a population of entities that reproduce, a view championed by Godfrey-Smith (2009). Several authors, following in Van Valen’s footsteps, have recently argued that important cases of evolution by natural selection must involve reproduction, and that differential persistence with or without differential growth can be sufficient (Bouchard 2008, 2011; Bourrat, 2014; Charbonneau 2014; Doolittle 2014; Doolittle and Inkpen 2018; for a review, see Papale 2021). Nonetheless, assuming a metapopulation, it is clear that populations with the ability to maintain or increase their size would out-compete those that are unable to do so. Thus, the ability for a population to sustain its population size might be regarded as a primordial form of adaptation without which other adaptations would be almost impossible to evolve.