How quickly could rabbits multiply if nothing stopped them? The answer is surprising and is a question that has intrigued mathematicians for centuries. Italian mathematician Leonardo Fibonacci was reflecting on the reproductive potential of rabbits as early as 1201. In his Book of Calculations, he explored how a population could grow from a single pair, leading to the mathematical pattern now known as the Fibonacci Sequence. Under Fibonacci’s assumptions, the rabbit population would eventually reach 466. But his model was based on some decidedly unnaturalistic assumptions; After all, Fibonacci was more of a mathematician than a biologist. So what happens if we build a different model? We asked statistical modeler Tom Fiddaman of Ventana Systems to crunch the numbers. Their scenario assumes that European rabbits produce an average of five offspring per litter and that their offspring reach sexual maturity at three months. Once mature, females produce one litter each month. The model also alternates the sex ratio of each litter: one litter contains three females and two males, followed by another with three males and two females. And there’s a more crucial assumption: none of the rabbits die. With all those conditions given, the population would reach 1,182 rabbits on New Year’s Eve. And that’s just the first year. By the end of the second year, the theoretical population would have ballooned to about 345,000 rabbits. In reality, of course, rabbit populations face many obstacles to such runaway growth. Disease, predation, and fluctuations in food availability help keep their numbers in check.
