Joshua V. Peñalba1, Anna Runemark2, Joana I. Meier3,4, Pooja Singh5,6, Guinevere O.U. Wogan7, Rosa Sánchez-Guillén8, James Mallet9, Sina J. Rometsch10,11, Mitra Menon12, Ole Seehausen5,6, Jonna Kulmuni13,14,16 and Ricardo J. Pereira15,16 1Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Center for Integrative Biodiversity Discovery, 10115 Berlin, Germany 2Department of Biology, Lund University, 22632 Lund, Sweden 3Tree of Life, Wellcome Sanger Institute, Hinxton, Cambridgeshire CB10 1SA, United Kingdom 4Department of Zoology, University of Cambridge, Cambridgeshire CB2 3EJ, United Kingdom 5Department of Aquatic Ecology, Institute of Ecology and Evolution, University of Bern, 3012 Bern, Switzerland 6Center for Ecology, Evolution & Biogeochemistry, Swiss Federal Institute of Aquatic Science and Technology (EAWAG), CH-8600 Kastanienbaum, Switzerland 7Department of Integrative Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA 8Red de Biología Evolutiva, INECOL, Xalapa, Veracruz, CP 91073, Mexico 9Organismal and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA 10Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06511, USA 11Yale Institute for Biospheric Studies, Yale University, New Haven, Connecticut 06511, USA 12Department of Evolution and Ecology, University of California Davis, Davis, California 95616, USA 13Department of Evolutionary and Population Biology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, 1098 XH Amsterdam, The Netherlands 14Organismal and Evolutionary Biology Research Programme, University of Helsinki, Biocenter 3, Helsinki, Finland 15Department of Zoology, State Museum of Natural History Stuttgart, Stuttgart 70191, Germany Correspondence: ricardojn.pereiragmail.com

↵16 These authors contributed equally to this work.

Hybridization, or interbreeding between different taxa, was traditionally considered to be rare and to have a largely detrimental impact on biodiversity, sometimes leading to the breakdown of reproductive isolation and even to the reversal of speciation. However, modern genomic and analytical methods have shown that hybridization is common in some of the most diverse clades across the tree of life, sometimes leading to rapid increase of phenotypic variability, to introgression of adaptive alleles, to the formation of hybrid species, and even to entire species radiations. In this review, we identify consensus among diverse research programs to show how the field has progressed. Hybridization is a multifaceted evolutionary process that can strongly influence species formation and facilitate adaptation and persistence of species in a rapidly changing world. Progress on testing this hypothesis will require cooperation among different subdisciplines.