But is evolution completely directed by natural selection or do non-Darwinian factors (non-selective factors: chance, neutral changes, bio-molecular side effects) play a significant role? Currently, the possibility of constructive neutral evolution (CNE) is discussed [2-5]. The CNE idea opens additional routes in biological inquiry that allow the development of neutral models, which can anchor molecular-evolution studies—designed to explain complexity as well as biodiversity—on grounds free of a priori adaptionist explanations. The scheme of CNE will supplement or may revolutionize our understanding of the origin, direction and meaning of life.
Carl Zimmer instructively put the origin of the term “constructive neutral evolution” into context :
In the 1990s a group of Canadian biologists started to ponder the fact that mutations often have no effect on an organism at all. These mutations are, in the jargon of evolutionary biology, neutral. The scientists, including Michael Gray of Dalhousie University in Halifax, proposed that the mutations could give rise to complex structures without going through a series of intermediates that are each selected for their help in adapting an organism to its environment. They dubbed this process “constructive neutral evolution.”
Keywords: life science, evolutionary theory, neutral theory, neo-Darwinian thinking, evolutionary genetics, bio-molecular complexity.
References and more to explore
 R. Dawkins: The Blind Watchmaker. Penguin Books, London, England, reprinted (from the 1986 Longman publication) with an appendix 1991.
 A. Stoltzfus: On the possibility of constructive neutral evolution. J. Mol. Evol. August 1999, 49 (2), pp. 169-181 [www.ncbi.nlm.nih.gov/pubmed/10441669].
 A. Stoltzfus: Constructive neutral evolutionary theory: exploring evolutionary theory's curious disconnect. Biology Direct 2012, 7:35. doi: 10.1186/1745-6150-7-35.
 C. Zimmer: The surprising origins of life's complexity. Sci. Am. August 2013, 309 (2), pp. 84-89 [www.scientificamerican.com/article.cfm?id=the-surprising-origins-of-evolutionary-complexity].
 Entropic Existence: Selection, Neutrality, and the Appearance of Design. April 23, 2010 [entropicexistence.blogspot.com/2010/04/selection-neutrality-and-appearance-of.html].