Modularity is a very important concept in nature. Modularity can be defined as subdivision of a complex object into simpler objects. The subdivision is determined either by the structure or function of the object and its subparts.
Modularity can be found everywhere; in living creatures as well as in inanimate objects. The subdivision in less complex objects is often not obvious.
At a very basic level electrons, positrons, and neutrons make the building blocks for any matter. At a higher level, atoms of elements are another form of simple modules of which everything is constructed. In living creatures proteins and on a higher level, cells could be seen as basic components. This idea of modules can be continued to more and more complex structures. Even looking at the universe planets can be seen as modules within a solar system.
Replication and decomposition are the two main concepts for modularity. These concepts are found in concrete objects as well as in thinking. It is often difficult to discriminate sharply between them; replication and decomposition often occur in combination.
Replication is a way of reusing knowledge. Once one module is developed and has proved to be useful it is replicated in a larger number. This principle is often found in living organisms. Observing a human this can be seen in a various scale: two similar legs, fingers, vertebra of similar structure, thousands of hair modules, and billions of cells. In electronics, the development of integrated circuits is based on replication of simple units to build a complex structure.
Decomposition is often found when dealing with a complex task. It is a sign of intelligent behaviour to solve a complex problem by decomposing it into simpler tasks which are easier to manage and then reassemble the solution from the results of the subtasks. Constructing large software, building a car, or solving an equation are usually done by decomposing the problem.