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.
The concept of evolution in this context refers to the dynamic balance between two species, foxes and rabbits, where changes in one population affect the other, resulting in a recurring pattern of growth and decline.