Why Does the Fibonacci Sequence Appear So Often in Nature?

In 1202, Italian mathematician Leonardo Pisano (also known as Leonardo Fibonacci, meaning "son of Bonacci") wondered how many rabbits a single set of parents could produce. More specifically, Fibonacci posed the question: How many pairs of rabbits can a single pair of rabbits produce 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 [source: Ghose].

Think about it: Two newborn rabbits are placed in an enclosed area where the rabbits begin to, well, breed like rabbits. Rabbits can't bear young until they are at least 1 month old, so for the first month, only one pair remains. At the end of the second month, the female gives birth to a new pair, leaving two pairs total.

When month three rolls around, the original pair of rabbits produces 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 for a total of five pairs of rabbits.

So after a year, how many rabbits would there be? That's when the mathematical equation comes in. It's pretty simple, despite sounding complex.

The first Fibonacci numbers go as follows: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144 and on to infinity.

The mathematical equation that describes it looks like this:

Basically, each integer is the sum of the preceding two numbers. (You can apply the concept to negative integers, but we're only going to cover the positive integers here.)

This set of infinite sums is known as the Fibonacci series or the Fibonacci sequence. The ratio between the numbers in the Fibonacci sequence (1.6180339887498948482...) is frequently called the golden ratio or golden number. The ratios of successive Fibonacci numbers approach the golden ratio as the numbers approach infinity.

Want to see how these fascinating numbers are expressed in nature? No need to visit your local pet store; all you have to do is look around you.

While some plant seeds, petals and branches, etc., follow the Fibonacci sequence, it certainly doesn't reflect how all things grow in the natural world. And just because a series of numbers can be applied to an astonishing variety of objects that doesn't necessarily imply there's any correlation between figures and reality.

As with numerological superstitions such as famous people dying in sets of three, sometimes a coincidence is just a coincidence.

But while some would argue that the prevalence of successive Fibonacci numbers in nature are exaggerated, they appear often enough to prove that they reflect some naturally occurring patterns. You can commonly spot these by studying the manner in which various plants grow. Here are a few examples:

Seed Heads, Pinecones, Fruits and Vegetables

Look at the array of seeds in the center of a sunflower and you'll notice they look like a golden spiral pattern. Amazingly, if you count these spirals, your total will be a Fibonacci number. Divide the spirals into those pointed left and right and you'll get two consecutive Fibonacci numbers.

You can decipher spiral patterns in pine cones, pineapples and cauliflower that also reflect the Fibonacci sequence in this manner [source: Knott].

Flowers and Branches

Some plants express the Fibonacci sequence in their growth points, the places where tree branches form or split. One trunk grows until it produces a branch, resulting in two growth points. The main trunk then produces another branch, resulting in three growth points. Then the trunk and the first branch produce two more growth points, bringing the total to five. This pattern continues, following the Fibonacci numbers.

Additionally, if you count the number of petals on a flower, you'll often find the total to be one of the numbers in the Fibonacci sequence. For example, lilies and irises have three petals, buttercups and wild roses have five, delphiniums have eight petals and so on.

Honeybees

A honeybee colony consists of a queen, a few drones and lots of workers. The female bees (queens and workers) have two parents: a drone and a queen. Drones, on the other hand, hatch from unfertilized eggs. This means they have only one parent. Therefore, Fibonacci numbers express a drone's family tree in that he has one parent, two grandparents, three great-grandparents and so forth [source: Knott].

Storms

Storm systems like hurricanes and tornadoes often follow the Fibonacci sequence. Next time you see a hurricane spiraling on the weather radar, check out the unmistakable Fibonacci spiral in the clouds on the screen.

The Human Body

Take a good look at yourself in the mirror. You'll notice that most of your body parts follow the numbers one, two, three and five. You have one nose, two eyes, three segments to each limb and five fingers on each hand. The proportions and measurements of the human body can also be divided up in terms of the golden ratio. DNA molecules follow this sequence, measuring 34 angstroms long and 21 angstroms wide for each full cycle of the double helix.

Why Do So Many Natural Patterns Reflect the Fibonacci Sequence?

Scientists have pondered the question for centuries. In some cases, the correlation may just be coincidence. In other situations, the ratio exists because that particular growth pattern evolved as the most effective. In plants, this may mean maximum exposure for light-hungry leaves or maximized seed arrangement.

While experts agree that the Fibonacci sequence is common in nature, there is less agreement about whether the Fibonacci sequence is expressed in certain instances of art and architecture. Although some books say that the Great Pyramid and the Parthenon (as well as some of Leonardo da Vinci's paintings) were designed using the golden ratio, when this is tested, it's found to be false [source: Markowsky].

Mathematician George Markowsky pointed out that both the Parthenon and the Great Pyramid have parts that don't conform to the golden ratio, something left out by people determined to prove that Fibonacci numbers exist in everything. The term "the golden mean" was used in ancient times to denote something that avoided access in either direction, and some people have conflated the golden mean with the golden ratio, which is a more recent term that came into existence in the 19th century.