Leonardo of Pisa, known as Fibonacci, described the sequence in 1202 with a puzzle about breeding rabbits. Each number is the sum of the two before it: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55.
Divide each number by the one before it and the answers settle towards 1.618, the golden ratio. It is the proportion that appears when a whole is split so that the whole is to the larger part as the larger part is to the smaller.
Plants grow new seeds and leaves at a fixed turn from the last one, and the turn that packs them most tightly is a golden-ratio fraction of a full circle. The spirals that result come in Fibonacci numbers: 34 one way and 55 the other on a typical sunflower.
1. Try It
Find a pine cone. Count the spirals winding one way, then the spirals winding the other. Then check the list. A pineapple works too, and so does a cauliflower.