Leonardo of Pisa (c. 1170 – c. 1250), or, most commonly, Fibonacci, was an Italian mathematician, considered by some as the most talented mathematician of the Middle Ages. Fibonacci is best known to the modern world for the spreading of the Arabic numeral system in Europe, as well as for a modern number sequence named after him known as the Fibonacci numbers.

In his book, the Liber Abaci, he posed and solved a problem involving the growth of a hypothetical population of rabbits based on idealized assumptions.

Suppose a newly-born pair of rabbits, one male, one female, are put in a field. Rabbits are able to mate at the age of one month so that at the end of its second month a female can produce another pair of rabbits. Suppose that our rabbits never die and that the female always produces one new pair (one male, one female) every month from the second month on. How many pairs will there be in one year ?

The solution, generation by generation, was a sequence of numbers later known as Fibonacci numbers: the number of existing pairs is the sum of the two previous numbers of pairs in the sequence.