That series of changes under natural law which involves
   continuous progress from the homogeneous to the heterogeneous in
   structure, and from the single and simple to the diverse and manifold
   in quality or function. The pocess is by some limited to organic
   beings; by others it is applied to the inorganic and the psychical. It
   is also applied to explain the existence and growth of institutions,
   manners, language, civilization, and every product of human activity.
   The agencies and laws of the process are variously explained by
   different philosophrs.