Citation: Göttert, T.; Perry, G. Going Wild in the City—Animal Feralization and Its Impacts on Biodiversity in Urban Environments. Animals 2023, 13, 747. https:// doi.org/10.3390/ani13040747 Academic Editor: Dimitrios Bakaloudis Received: 28 January 2023 Revised: 13 February 2023 Accepted: 16 February 2023 Published: 19 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). animals Review Going Wild in the City—Animal Feralization and Its Impacts on Biodiversity in Urban Environments Thomas Göttert 1, * and Gad Perry 2 1 Research Center [Sustainability–Transformation–Transfer], Eberswalde University for Sustainable Development, 16225 Eberswalde, Germany 2 Department of Natural Resource Management, Texas Tech University, Lubbock, TX 79409, USA * Correspondence: thomas.goettert@hnee.de Simple Summary: Understanding the impact of urbanization on biodiversity is a crucial task of our time. Here, we reflect on the importance of feralization in the relationship between ongoing urbanization and the worsening biodiversity crisis. Feralization is often viewed as the exact opposite of a domestication process—a perception that we argue is too simplistic. The interrelations between domestication, feralization, and the adaptation of taxa to novel, human-made environments such as cities are complex. Given their unique traits, feral(izing) taxa can play key roles in sustainability, sometimes problematic (i.e., invasive species) but at other times, improving human well-being in urban settings. Abstract: Domestication describes a range of changes to wild species as they are increasingly brought under human selection and husbandry. Feralization is the process whereby a species leaves the human sphere and undergoes increasing natural selection in a wild context, which may or may not be geographically adjacent to where the originator wild species evolved prior to domestication. Distinguishing between domestic, feral, and wild species can be difficult, since some populations of so-called “wild species” are at least partly descended from domesticated “populations” (e.g., junglefowl, European wild sheep) and because transitions in both directions are gradual rather than abrupt. In urban settings, prior selection for coexistence with humans provides particular benefit for a domestic organism that undergoes feralization. One risk is that such taxa can become invasive not just at the site of release/escape but far away. As humanity becomes increasingly urban and pristine environments rapidly diminish, we believe that feralized populations also hold conservation value. Keywords: Anthropocene; domestication; feralization; urbanization; invasive species; biodiversity in novel ecosystems 1. Introduction Humans continue to modify Earth in profound ways, some such as global climate change relatively recently and others as part of long-lasting processes. Here, we focus on the interaction between two of the latter: domestication of other species and the feralization that occasionally follows, and urbanization. Although historically and mechanistically different, we argue that the two interact in important ways. We briefly review each process by itself, then assess the ways they interact in a conservation context. 2. Domestication and Feralization In domestication, a wild species of plant or animal is removed from its ecological and evolutionary context and progressively incorporated into the human sphere [1]. During this process, it is subject to strong evolutionary pressures under anthropogenic selection and becomes an increasingly better fit to the human template. Artificial selection during this transformation produces new forms, as when a wolf (Canis lupus) is domesticated. Despite Animals 2023, 13, 747. https://doi.org/10.3390/ani13040747 https://www.mdpi.com/journal/animals