The sequence takes its name from Leonardo of Pisa, known as Fibonacci, who introduced it to European readers in his 1202 book Liber Abaci through a puzzle about breeding rabbits. Indian scholars had described the same numbers centuries earlier while counting the ways to arrange long and short syllables in poetry. The rule could hardly be simpler — each number is the sum of the two before it — yet it produces a pattern that mathematicians have been unpacking ever since.
Divide any term by the one before it and the answer settles closer and closer to roughly 1.618, the golden ratio, a proportion that artists and architects have used for centuries and that turns up in the geometry of pentagons and five-pointed stars. The same number governs the angle at which many plants place each new leaf or seed: spacing them by about 137.5 degrees means no two ever line up, so each one gets light and room. That is why the seed heads of sunflowers, the scales of pine cones and the florets of a pineapple all show interlocking spiral families whose counts are Fibonacci numbers.
The pattern is genuinely common in nature, though it is often overstated — nautilus shells, for instance, spiral at a different proportion than the golden one they are usually credited with. What makes the sequence worth exploring is how much visible structure follows from one line of arithmetic, and how sharply that structure depends on the numbers you start from and the angle you choose. Nudging the divergence angle by a fraction of a degree scatters the neat spiral arms into a mess, which is the clearest demonstration of why plants converged on this particular value.