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Essay

Nature 446, 860 (19 April 2007) | doi:10.1038/446860a; Published online 18 April 2007

Connections Rules of engagement

John Doyle1 & Marie Csete2

  1. John Doyle is at the California Institute of Technology, Pasadena, California 91125-8100, USA
  2. Marie Csete is at Emory University, Atlanta, Georgia 30322, USA.
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Complex engineered and biological systems share protocol-based architectures that make them robust and evolvable, but with hidden fragilities to rare perturbations.

Chaos, fractals, random graphs and power laws inspire a popular view of complexity in which behaviours that are typically unpredictable and fragile 'emerge' from simple interconnections among like components. But applied to the study of highly evolved systems, this attractively simple view has led to widespread confusion.