Hybrid zones provide a powerful opportunity to analyze ecological and evolutionary interactions between divergent lineages. As such, research on hybrid zones has played a prominent role in the fields of evolutionary biology and systematics. Herein, we clarify what hybrid zones are, what is (and is not) known about them, and how different types of genomic data contribute to our understanding of hybrid zones. We then review two key topics, namely, what genomic analyses of hybrid zones have revealed about the basis and dynamics of speciation and how hybrid zones directly affect evolutionary processes. In the latter case, we emphasize the importance of contingency and ecological and genomic context in outcomes of hybridization. Throughout, we highlight limitations and key unknowns, and suggest approaches most likely to advance our understanding of hybrid zones and evolutionary processes in general.


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