As mammals that live in the water, whales have been an enigma since the time of Darwin. In the past 20 years, biologists and paleontologists have uncovered a remarkably complete story of whales’ transition from land to water. The evolution of whales provides an excellent example of how biologists use a variety of types of evidence to understand evolution. This lesson introduces students to a small portion of the fossil, biochemical, and genetic information that is known about the evolution of whales.