Genetics and genomics of hybridization.

Once considered rare in some species groups, we now appreciate that hybridization between distinct lineages is a feature of essentially all branches of the eukaryotic tree of life. Determining the drivers of hybridization across species and locally along genomes is not just a question of history; it is fundamental to understanding genomic variation, adaptation and even disease risk across diverse species. Here, we start by reviewing methodological advances that may improve our understanding of the frequency of hybridization and its evolutionary effects. Next, we compile results from traditional and genomic sources of evidence to estimate the incidence of hybridization in nature and discuss the causes and consequences of this key evolutionary process. Finally, we highlight open questions, including whether hybridization promotes diversification, and how such questions could be addressed in the future.