Introduction
As news reports often emphasize, humans have a large effect on the environment. We change the global climate, pollute the water and air, convert large tracts of natural habitat into farmland and urban areas, drain wetlands, and reduce the population sizes of species we hunt for food (e.g., fishes) or use as resources (e.g., trees).
Although we have taken steps to limit some of the damage we cause to biological communities, human actions have consequences that we have barely begun to recognize, much less address: we cause evolutionary change.In this chapter, we'll examine what evolution is and how it affects ecological interactions, as well as how ecological processes influence evolutionary change. At the close of the chapter, we'll focus specifically on how humans cause evolutionary change. Our goal in this chapter is not to provide a comprehensive survey of evolutionary biology—for that, see the textbooks on evolution listed in the Suggested Readings on the book's website. Instead, our aim is to show that ecology and evolution are interconnected, a theme to which we will return in later chapters of this book. We'll begin by considering two ways in which evolution can be defined.