All the complex systems we can observe, from organisms to ecosystems, have developed from simpler beginnings. A human life, for instance, develops from a single cell, whose descendants differentiate as they divide and multiply. A fully developed human body has thousands of different types of cells, each doing its separate job to maintain the organic unity of the whole. This quality of highly differentiated unity is what we call complexity.
Differentiation refers to the degree to which a system (i.e. an organ such as the brain, or an individual, a family, a corporation, a culture, or humanity as a whole) is composed of parts that differ in structure or function from one another. Integration refers to the extent to which the different parts communicate and enhance one another’s goals. A system that is more differentiated and integrated than another is said to be more complex.
— Csikszentmihalyi (1993, 156)
Uniformity and conflict are degenerate forms of unity and diversity respectively. Complexity is the logical product of unity and diversity, just as development (or evolution) is the logical product of change and continuity, and information is the logical product of breadth and depth (see Chapter 10· or Fuhrman 2010).