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Abstract Competition for mates can play a critical role in determining reproductive success, shaping phenotypic variation within populations, and influencing divergence. Yet, studies of the role of sexual selection in divergence and speciation have focused disproportionately on mate choice. Here, we synthesize the literature on how mate competition may contribute to speciation and integrate concepts from work on sexual selection within populations—mating systems, ecology, and mate choice. Using this synthesis, we generate testable predictions for how mate competition may contribute to divergence. Then, we identify the extent of existing support for these predictions in the literature with a systematic review of the consequences of mate competition for population divergence across a range of evolutionary, ecological, and geographic contexts. We broadly evaluate current evidence, identify gaps in available data and hypotheses that need testing, and outline promising directions for future work. A major finding is that mate competition may commonly facilitate further divergence after initial divergence has occurred, e.g., upon secondary contact and between allopatric populations. Importantly, current hypotheses for how mate competition contributes to divergence do not fully explain observed patterns. While results from many studies fit predictions of negative frequency-dependent selection, agonistic character displacement, and ecological selection, results from ~30% of studies did not fit existing conceptual models. This review identifies future research aims for scenarios in which mate competition is likely important but has been understudied, including how ecological context and interactions between mate choice and mate competition can facilitate or hinder divergence and speciation. 

Abstract Ever since the Modern Synthesis, a debate about the relationship between microevolution and macroevolution has persisted—specifically, whether they are equivalent, distinct, or explain one another. How one answers these questions has become shorthand for a much broader set of theoretical debates in evolutionary biology. Here, we examine microevolution and macroevolution in the context of the vast proliferation of data, knowledge, and theory since the advent of the Modern Synthesis. We suggest that traditional views on microevolution and macroevolution are too binary and reductive given current empirical and theoretical advances in biology. For example, patterns and processes are interconnected at various temporal and spatial scales and among hierarchical entities, rather than defining micro- or macro-domains. Further, biological entities have variably fuzzy boundaries, resulting in complex evolutionary processes that influence macroevolution occuring at both micro- and macro-levels. In addition, conceptual advances in phylodynamics have yet to be fully integrated with contemporary macroevolutionary approaches. Finally, holding microevolution and macroevolution as distinct domains thwarts synthesis and collaboration on important research questions. Instead, we propose that the focal entities and processes considered by evolutionary studies be contextualized within the complexity of the multidimensional, multimodal, multilevel phylogenetic system.