The present state of the universe lies somewhere between two extremes of uniformity: perfect order, or zero entropy, which might have happened at the beginning of time (big bang), and total disorder, infinite entropy, which could be its final destiny (heat death). Somehow from these homogeneous extremes, diversity arises in the form of galaxies, planets, heavy atoms, life.
Analogous scenarios of emergence of organization exist within the scope of different sciences (e.g. formation of ecological niches, of human language, of macromolecules, of the genetic code, etc.). The study of evolution of complexity bears on these disciplines and aims at understanding the general features of such phenomena of ``complexification'': what is complexity, and what kinds of processes lead to it? [77,64].
Biology in particular strives to explain the evolution of complex life forms starting from a random ``primitive soup''. Darwin's theory of natural selection is the fundamental theory that explains the changing characteristics of life in our planet, but contemporary Darwinism is far from complete, having only begun to address questions such as specialization, diversification and complexification.
Some theories of natural evolution argue that complexity is nothing but statistical error , whereas others propose that increasing complexity is a necessary consequence of evolution [122,63]. The point of view of universal Darwinism  is that the same characteristics of life on earth that make it susceptible to evolutionary change by natural selection, can also be found on other systems, which themselves undergo evolutionary change. Plotkin  proposes the g-t-r heuristics1.1 as the fundamental characteristic of evolutionary process. Three phases are involved: