Sociocultural evolution, sociocultural evolutionism or cultural evolution are theories of cultural and social evolution that describe how cultures and societies change over time. Whereas sociocultural development traces processes that tend to increase the complexity of a society or culture, sociocultural evolution also considers process that can lead to decreases in complexity (degeneration) or that can produce variation or proliferation without any seemingly significant changes in complexity (cladogenesis). Sociocultural evolution is ""the process by which structural reorganization is affected through time, eventually producing a form or structure which is qualitatively different from the ancestral form"".(Note, this article focusses on that use of the term 'socio-cultural evolution' to refer to work that is not in line with contemporary understandings of the word 'evolution'. There is a separate body of academic work which uses the term 'cultural evolution' using a more consensus Darwinian understanding of the term 'evolution'. For a description of this work, based in the foundational work of DT Campbell in the 1960s and followed up by Boyd, Richerson, Cvalli-Sforza, and Feldman in the 1980s, go to Cultural evolution or Dual inheritance theory.)Most 19th-century and some 20th-century approaches to socioculture aimed to provide models for the evolution of humankind as a whole, arguing that different societies have reached different stages of social development. The most comprehensive attempt to develop a general theory of social evolution centering on the development of socio-cultural systems, the work of Talcott Parsons (1902-1979), operated on a scale which included a theory of world history. Another attempt, on a less systematic scale, originated with the world-systems approach.More recent approaches focus on changes specific to individual societies and reject the idea that cultures differ primarily according to how far each one is on the linear scale of social progress. Most modern archaeologists and cultural anthropologists work within the frameworks of neoevolutionism, sociobiology and modernization theory.Many different societies have existed in the course of human history, with estimates as high as over one million separate societies; however, as of 2013, only about two hundred or so different societies survive.