Evolution is responsible for all biological diversity on earth, so it is critical that the students understand precisely what evolution is and how we know that evolution is a fact. In this chapter the four causes of evolutionary change in populations are reviewed in some detail, relying partially on the lessons on genetics in Chapter 5. It particularly emphasizes evidence in the modern world for evolution, such as the evolution of antibiotic-resistant strains of bacteria, but also patterns seen in extant vertebrates documented in locations of significant environmental change over the last 200 years. This chapter also reviews the history of the discovery of evolution, and the intellectual antecedents that allowed Darwin to make his inference. It explores the appearance of the scientific worldview during the Renaissance and Enlightenment and how that worldview challenged (and continues to challenge) some religious and secular authorities.