Everyone knows what a species is, don’t they? The bear, the wolf, the shark, etc. So why a whole book on species? Well, the answer is that not everyone really knows what a species is; not because people are ignorant, but because defining species is far from simple and straightforward. Furthermore, and even more counterintuitively for us, there are no exemplars of species, nor sets of distinctive features that we can use to distinguish among them. There is no exemplar of any species. There is no such thing as ‘the bear’, ‘the wolf’ or ‘the shark’, but a variety of bears, wolves and sharks; they share some common features but exhibit an enormous variation in others. As John Wilkins explains in this fascinating book, humans have been preoccupied with classifying organisms around them since ancient times. Yet there has never been a single best way to do this, or to define species, which is the fundamental unit of this classification. Wilkins explains why there exist different definitions that can be in competition with each other or can be consistent with each other. Most importantly, he shows that depending on which species definition we use, we can end up with very different results with respect to classification. Yet, despite problems such as these, species is a useful concept in science. And as Wilkins concludes, understanding is not about acquiring a single true answer or definition. Rather, it is becoming aware of the different uses of a concept, and the different contexts of this use. Reading this book will make you feel that often understanding is about realising how much we do not know. But this is exactly the pleasure of understanding: realising that there is more out there than simplistic accounts can provide. The more you come to know, the more you realise how much else you do not know. Reading this book will make you experience this rewarding feeling.

Kostas Kampourakis, Series Editor