 Have you ever heard of the peppered moth? It's a supposed example of evolution often used in biology classrooms. Here's the story in many textbooks. Before the Industrial Revolution, birds saw and ate more of the dark variety of peppered moths sitting on tree trunks. Then as pollution increased, they saw more of the light ones, and the population shifted to mostly dark moths. Then as pollution declined, it shifted back to light moths again. It's evolution in action.