Fibula Structure and Function
The fibula is one of the two bones located in the lower legs of humans. These are sometimes also referred to as the "hind legs". The fibula is not actually the weight bearing bone of the leg, so what is the the purpose of the fibula? It actually has some purpose on it's own and these purposes can easily be seen when you consider certain elements of human lives.
First, consider what the bone structure of some others animals is and what they do in life. For instance, the horse only has one lower leg bone. What does a horse do and how is the horse built? The horse does nothing more with their appendages than walk on them. Man on the other hand has arms as well as legs, so that the legs may serve more of a purpose than simply for walking. Birds also only have one bone in their lower leg. Though birds do walk, they do not use their legs primarily for walking or climbing, but instead use them mostly for stability as they perch.
Now let's take a look at humans and what they use their legs for. Humans walk, run and use their legs for stability and to be able to stand upright, but they also have other uses. For instance, humans may use their legs to climb with. The existence of the fibula offers us more maneuverability than we would have with only one leg bone.
Consider the tibia. It is the weight bearing bone of the legs, but the fibula offers secondary support to the tibia. Think of the fibula as you would think of the support braces for a table. While they aren't actually bearing any weight, they do offer support to the actual table legs, which in turn lends those table legs strength to prevent wobbling of the table.