Recursion in Nature

Numerous living things show a structure that could be described as recursive, even if it is not quite as regular as simple mathematical functions.

The vascular system of both plants and animals demonstrates this structure. Consider the veins of a tree leaf, such as a maple. The vein will either continue without branching, or it will branch into three smaller veins. Each of these smaller veins will do the same, that is, continue or subdivide further. This is a recursive structure. A similar description could be made of the branches of a tree or the arteries in any higher animal.

The Fibonacci sequence, which has a recursive definition, is seen in a number of different places in nature. The sequence is related to the logarithmic spiral which is seen in snail shells. Somewhat more interesting is that in sunflower heads, the seeds form logarithmic spirals from the center. Moreover, if you count the clockwise and counterclockwise spirals, you will usually get two successive terms in the Fibonacci sequence.