Cover image:

Vinap/Shutterstock

Figures 2.1, 2.2, 2.4–2.11, 3.1–3.9, 4.1–4.7, 4.9–4.17, 5.1–5.11, 6.1–6.10, 7.1–7.4, 8.1–8.8, 9.2–9.8, 10.1–10.6, 11.1–11.8, 11.10, 12.1–12.9, 13.1–13.8, 14.1–14.7, 15.1–15.4:

Courtesy of Gabrielle Benefield

Figure 2.3:

John R. Boyd