Ecosystem's 80th and the Reemergence of Emergence

‘‘Ecosystem’’ turned eighty this July. When Tansley (1935) coined the term, he did so largely as a rejection of the concept of emergence as espoused by Phillips (1935). The Phillips paper actually came out a month after Tansley’s, but Tansley was editor for the Journal of Ecology at the time and he published Phillip’s paper with a footnote on the first page that can only be viewed as a disclaimer. Tansley (1935) left no doubt about his feelings in the title of his response: ‘‘The Use and Abuse of Vegetation Concepts and Terms.’’ However, Tansley’s struggle with the concept of emergence precedes his clash with Phillips and is very clearly presented in a 1932 Lecture to Magdalen Philosophy Club of Oxford University, which was posthumously published by Ecosystems in 2002 (Tansley 2002). Emergence has since reemerged and has again entered the lexicon of ecologists. However, it is not always clear what is meant by an ‘‘emergent property’’; often it seems that the concept is invoked simply to express surprise at some apparently complex system-level property. Our aim here is not to present a comprehensive review and analysis of the various concepts of Emergence; the format is too short and there are others far better qualified (for example, Broad 1925; Birch and Cobb 1981; Blew 1996; Chalmers 2003; Reid 2007; Abel 2009). Our aim is to celebrate Tansley’s (1935, 2002) great contribution to Ecology, to reflect on the irony of the apparent reemergence of a concept rejected by Tansley (1935), and to draw distinctions among various concepts all called ‘‘emergence.’’ The problem, as we see it, is that there are at least three distinct concepts being labeled ‘‘emergence’’: The first of the three concepts is what Bedau (1997) calls ‘‘Strong Emergence.’’ Under this concept, objects at higher levels of organization acquire ‘‘emergent properties’’ that are not explainable in terms of the interactions among their constituent parts. There must therefore be some external causative agent acting toward the emergence of these properties (for example, Morgan 1923) or they arise spontaneously only in the context of the higher level object (Broad 1925). The ideas underlying strong emergence are what inspired Tansley (1935), in a rejection of the concept, to coin the term ‘‘Ecosystem.’’ We will use the term ‘‘Teleological Emergence’’ to describe this concept because it is more descriptive than ‘‘Strong Emergence.’’ The second of the concepts is what Bedau (1997) calls ‘‘Weak Emergence’’ (an unfortunate name for a strong concept). This concept is derived from the study of complex systems and is applied to chaotic phenomena like fractals and strange attractors that arise from nonlinear interactions in a system that are sensitive to initial conditions. We will use the more descriptive term ‘‘Chaotic Emergence’’ for this concept. Some aspects of teleological and chaotic emergence appear superficially similar; however, the underlying foundations differ significantly, and in particular, the attributions of causation explicit in the two concepts are diametrically opposed. The third of the concepts we will call ‘‘Mechanistic Emergence.’’ This concept, we believe, adheres more closely to the common usage of the Received 27 May 2015; accepted 27 May 2015; published online 6 June 2015 Author contributions The manuscript is derived from a longstanding philosophical debate between the authors. Both authors contributed to the writing. *Corresponding author; e-mail: erastett@mbl.edu Ecosystems (2015) 18: 735–739 DOI: 10.1007/s10021-015-9893-6