Murielle Ålund1,17, Meredith Cenzer2,17, Nicolas Bierne3, Janette W. Boughman4, José Cerca5, Mattheau S. Comerford6, Alessandro Culicchi7, Brian Langerhans8, S. Eryn McFarlane9,10, Markus H. Möst11, Henry North12, Anna Qvarnström13, Mark Ravinet14, Richard Svanbäck15 and Scott A. Taylor16 1Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala 75236, Sweden 2Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, USA 3ISEM, Université de Montpellier, CNRS, IRD, Montpellier 34095, France 4Department of Integrative Biology, Michigan State University, East Lansing, Michigan 48824, USA 5CEES - Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, Oslo 0316, Norway 6Biology Department, UMass Boston, Boston, Massachusetts 02125, USA 7Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala 75236, Sweden 8Department of Biological Sciences, North Carolina State University, Raleigh, North Carolina 27695, USA 9Department of Botany, University of Wyoming, Laramie, Wyoming 82071, USA 10Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada 11Research Department for Limnology, University of Innsbruck, Innsbruck 6020, Austria 12Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom 13Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala 75236, Sweden 14School of Life Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom 15Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala 75236, Sweden 16Department of Ecology and Evolutionary Biology, University of Colorado Boulder, Boulder, Colorado 80309, USA Correspondence: murielle.alundebc.uu.se; mlcenzerucdavis.edu

↵17 Co-first authors contributed equally to this work; all other authors listed alphabetically.

Anthropogenic impacts on the environment alter speciation processes by affecting both geographical contexts and selection patterns on a worldwide scale. Here we review evidence of these effects. We find that human activities often generate spatial isolation between populations and thereby promote genetic divergence but also frequently cause sudden secondary contact and hybridization between diverging lineages. Human-caused environmental changes produce new ecological niches, altering selection in diverse ways that can drive diversification; but changes also often remove niches and cause extirpations. Human impacts that alter selection regimes are widespread and strong in magnitude, ranging from local changes in biotic and abiotic conditions to direct harvesting to global climate change. Altered selection, and evolutionary responses to it, impacts early-stage divergence of lineages, but does not necessarily lead toward speciation and persistence of separate species. Altogether, humans both promote and hinder speciation, although new species would form very slowly relative to anthropogenic hybridization, which can be nearly instantaneous. Speculating about the future of speciation, we highlight two key conclusions: (1) Humans will have a large influence on extinction and “despeciation” dynamics in the short term and on early-stage lineage divergence, and thus potentially speciation in the longer term, and (2) long-term monitoring combined with easily dated anthropogenic changes will improve our understanding of the processes of speciation. We can use this knowledge to preserve and restore ecosystems in ways that promote (re-)diversification, increasing future opportunities of speciation and enhancing biodiversity.