Population Fluctuation is a computer model of a world populated by eagles, mice, and grain. The three populations make up a simple food chain: the eagles eat the mice, the mice eat the grain, and the grain just grows. By adjusting variables such as the intelligence of the eagles and mice and the strength of each of the three species, the visitor changes the balance of life in the model world. Small changes in the relative intelligence and strength of one species can lead to extinction for all.