In developing his argument that natural selection can explain the complex adaptations of organisms, Dawkins' first concern is to illustrate the difference between the potential for the development of complexity as a result of pure randomness, as opposed to that of randomness coupled with cumulative selection. He demonstrates this by the example of the weasel program. Dawkins then describes his experiences with a more sophisticated computer model of artificial selection implemented in a program also called "The Blind Watchmaker", which was sold separately as a teaching aid.