Paul Andersen describes genetic drift as a mechanism for evolutionary change. A population genetics simulator is used to show the importance of large population size in neutralizing random change. The near extinction of the northern elephant is used as an example of the bottleneck effect. The high incidence of total colorblindness due to a typhoon that hit the small island of Pingelap is also included.

Paul Andersen explains how life has evolved and continues to evolve today. A brief discussion of artificial, natural and sexual selection is included. The beak of the finch is used to explain how directional selection is achieved.

Crash Course Biology #18 - Hank talks about population genetics, which helps to explain the evolution of populations over time by combing the principles of Mendel and Darwin, and by means of the Hardy-Weinberg equation.