That's the story behind that Fibonacci sequence. I forget the exact details, but many years ago Fibonacci was given this problem, "If I have two rabbits. . . " and the solution he found was, 1,1,2,3,5,8,.... It also gave me an image to use :). Another interesting thing is that things in nature, such as flowers, seem to show numbers relating to the sequence. Almost all flowers have a number of petals that is a number in the Fibonacci sequence :) (normally, pluck a few out, and I might be wrong ;).