Motoo Kimura began the neutralist-selectionist divide when, in 1969, he hypothesized that most substitutions of amino acids in proteins are selectively neutral and developed the neutral theory of molecular evolution. While neutralism began as an empirical claim, it transformed into a methodology investigating evolutionary patterns ignoring selection. Where selectionists look first for the effects of natural selection, neutralists look first for the effects of drift, migration, and mutations. This methodological divide expanded first to paleobiology and then community ecology, and later beyond biology to economics and linguistics. Biologists, historians, and philosophers of science understand this divide well in evolution, partially in paleobiology, and barely in community ecology. But they have not noticed it beyond biology, and have not appreciated that it has the general methodological divide it is. Anywhere scientists investigate abundance patterns and favor selection explanations, neutralists seem likely to appear. Why is this? In this talk I will show that epistemic, sociological, and historical factors are all responsible. Data for abundance patterns is poor for most natural systems, and it is difficult to establish that selection is operating. This gives rise alternatively to groups of scientists who double-down on finding selection and who ignore selection. These episodes are not independent, however. For example, Stephen Jay Gould migrated between evolution and paleobiology and Daniel Simberloff between community ecology and paleobiology, each carrying tools and methods along. Analyzing this divide with these factors will enrich our understanding of why biologists use the methodologies that they do.
