Introduction

All living forms coexist with one another across the planet. Scientists estimate that roughly 8.7 million eukaryotic species exist on Earth, yet studies suggest that about 86% of species on land and 91% of those in the seas remain undiscovered, undescribed and uncatalogued. Even though humans sit at the top of this hierarchy, we remain deeply dependent on plants and animals — for food, as a source of labour in farming, as pets, and for a wide range of other economic benefits. Understanding animals and their characteristics, habitats, behaviour and evolutionary relationships is therefore genuinely important, and this chapter works through that understanding step by step: the diversity of the living world, why classification is needed, the different types of classification, the taxonomic hierarchy, nomenclature, and the tools used to study taxonomy.