   Biological individuality is much more varied and heterogeneous than previously believed and this additional complexity puts pressure on the notion that reproductive success can act as a ‘universal currency’ of fitness. The difficulties of establishing reproductive success for some clonal organisms, for collectives of organisms and for multi-species assemblages has led some biologists and philosophers to entertain alternative concepts of fitness. Leigh Van Valen, in his attempts to develop a theory of evolution that would allow for the evolution of whole communities (Van Valen 1975, 1989, 1991), suggested that fitness as energy control could explain the evolution of a broader range of biological systems. “Rather than saying that natural selection is expected differential reproduction, we should say that it is expected differential expansion” (Van Valen 1989, 7). By ‘expansion’ Van Valen doesn’t mean expansion in physical space (although that may occur) but expansion in resource or energy space. In this approach, energy is seen as the ‘universal currency’: a fitter community is one that controls more energy than another community. For ‘simpler’ biological systems such as sexual species with discrete generations, increased reproductive success is a good proxy for increased energy success and therefore previous measurements and models of reproductive output remain useful but their explanatory exhaustiveness is relativized. Although energy can seem to be a universal measure of fitness that could apply to the all the varied types of biological individuals that can emerge, it’s not clear that Van Valen’s approach can be as universal as desired since it has difficulty explaining increases in efficiency in energy control (see Bouchard 2004 chap 3 for analysis). This has motivated Bouchard (2004, 2008, 2011) to argue for an account of evolution focusing on differential persistence (reminiscent of Thoday 1953). Bouchard (2004, 2008, 2011) argues that Persistence Through Time of a lineage is the property maximized by evolution by natural selection: maximization of relative reproductive success or maximization of energy control are only two dominant strategies for persistence increase (see Bourrat 2014 and Doolittle 2014 for related approaches). In this approach (lineage) \(X\)is fitter than (lineage) \(Y\) if \(X\)has a higher propensity to persist for \(Z\) amount of time than \(Y\). Some of the problems of propensities remain, but we gain a way to assess ecological fitness (probability of persistence) in a way that can be independent of reproductive success. Persistence is the overarching design-problem. Increased reproductive potential is but one powerful way to increase one’s potential to persist.