Conserved Polymorphism, Fossils, and the Macroevolutionary Reach of Microevolution

AbstractCharles Darwin established modern evolutionary biology with his insight that the engine of global biodiversity is fueled by individual differences inherent to all populations. One hundred and sixty-seven years later, the concepts and mechanisms that bridge this macro- to microevolutionary spectrum remain highly sought after. In this essay, we explore phenotypic evolution at the interface of micro- and macroevolution from the perspective of morphology-based systematics by addressing the hypothesis that intraspecific polymorphism can be phylogenetically conserved. We begin by setting a theoretical footing for this "multispecies zone of polymorphism" by synthesizing recent contributions from population biology and phylogenomics regarding the timescale of microevolutionary dynamics. Next, we derive from this hypothesis predictions that can be tested with broad-based phenotypic sampling and discuss how these predictions align with expected patterns of homoplasy. We then use paleontology and its unique sampling potential as a lens to examine how conserved polymorphism may be shaping macroevolutionary inferences and outline future work. These efforts emphasize that the micro-macro interface remains a critical yet understudied aspect of phenotypic evolution with potentially far-reaching implications. The benefits of resolving these dynamics extend well beyond the best practices of phylogenetic reconstruction, as they reflect the very nature of the micro-macroevolutionary dichotomy in evolutionary theory.