Evolution is a mathematical model of a simplified ecosystem of foxes and rabbits using the Lotka–Volterra equations. The logic was that too small a population of rabbits would provide insufficient food for foxes whose numbers would then decline, until too few foxes would result in the rabbit population again increasing, and the cycle would continue.
This model illustrates the cyclical nature of predator-prey relationships in an ecosystem, where fluctuations in population sizes lead to a continuous cycle of growth and decline.