In 1202, Italian mathematician Leonardo Pisano (also known as Fibonacci, meaning “son of Bonacci”) pondered the question: Given optimal conditions, how many pairs of rabbits can be produced from a single pair of rabbits in one year? This thought experiment dictates that the female rabbits always give birth to pairs, and each pair consists of one male and one female.
Think about it — two newborn rabbits are placed in a fenced-in yard and left to, well, breed like rabbits. Rabbits can’t reproduce until they are at least one month old, so for the first month, only one pair remains. At the end of the second month, the female gives birth, leaving two pairs of rabbits. When month three rolls around, the original pair of rabbits produce yet another pair of newborns while their earlier offspring grow to adulthood. This leaves three pairs of rabbit, two of which will give birth to two more pairs the following month.
The order goes as follows: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144 and on to infinity. Each number is the sum of the previous two. This series of numbers is known as the Fibonacci numbers or the Fibonacci sequence. The ratio between the numbers (1.618034) is frequently called the golden ratio or golden number.
At first glance, Fibonacci’s experiment might seem to offer little beyond the world of speculative rabbit breeding. But the sequence frequently appears in the natural world — a fact that has intrigued scientists for centuries.