Lewontin's recipe for adaptation requires three ingredients: variation among individuals, heritability of that variation, and differential fitness. Mix these in a population, and adaptation follows. This is the standard framework for understanding how complex structures arise without design.
Arthur (arXiv:2602.20883) argues that the recipe is too narrow. Lewontin's version requires populations — multiple individuals competing for reproductive success. But adaptation occurs without populations. Clonal organisms adapt without reproductive variation. Holobionts — organisms plus their microbiomes — adapt through symbiotic adjustments that don't involve the host's reproduction at all. Neural networks adapt through weight updates within a single training run, with no population of networks competing.
The general principle is cumulative selection: small modifications are retained if they improve function, discarded if they don't, and the retained modifications accumulate. Lewontin's recipe is one implementation — variation through reproduction, heritability through genetics, fitness through survival. But other implementations exist: variation through somatic mutation, heritability through epigenetic persistence, fitness through developmental stability. Variation through synaptic fluctuation, heritability through weight updates, fitness through loss reduction.
The shift is from a specific mechanism (population genetics) to a general principle (cumulative selection). The principle requires only that modifications be generated, evaluated, and selectively retained. How the modifications are generated, what evaluates them, and how retention works are free parameters. Populations are one solution. Single organisms adapting over a lifetime are another. Algorithms optimizing a loss function are a third.
The general observation: when a process achieves the same outcome through multiple mechanisms, the explanation lives at the level of the principle, not the mechanism. Adaptation is not fundamentally about populations. It is fundamentally about cumulative selection, and populations are one of several substrates that implement it.