Living systems theory and other theory and research in the systems sciences and complexity science has illuminated many aspects of how living systems work—their mechanisms, processes and relationships. The Synergism Hypothesis, originally proposed in 1983, addresses the evolution of cooperative phenomena in nature and why there has been a secular trend over time toward increased complexity in living systems. This theory highlights the role of functional synergy—adaptively significant combined effects that are interdependent and otherwise unattainable—in shaping the ‘progressive’ emergence of complex living systems. This approach is entirely consistent with modern evolutionary biology and natural selection theory and is thus radically opposed to various orthogenetic/deterministic theories of complexity that have been proposed over the years. The Synergism Hypothesis has recently gained scientific support, and there is growing appreciation for the role of various kinds of synergy as an influence in the evolutionary process. Copyright © 2013 John Wiley & Sons, Ltd.