Rules of engagement among complex systems

A recent essay, “Rules of engagements “ by Doyle and Csete, published in Nature (1) starts with the following sentence:: “Complex engineered and biological systems share protocol-based architectures that make them robust and evolvable, but with hidden fragilities to rare perturbations.” I agree with the authors that “engineers can learn from biology” and wonder whether they grasped the essence of biological (life) complexity. The authors assure us that:” Biological systems are robust and evolvable in the face of even large changes in environment and system components, yet can be extremely fragile to small perturbations. Such universally robust yet fragile (RYF) complexity is found wherever we look.” True, life is universally robust but is it really fragile? Take for instance diabetes and cancer which the authors regard as: “conditions resulting from faulty biological control mechanisms, normally so robust as to go unnoticed.” Even the authors imply that these diseases are far from being fragile. So what led them astray?

It all started when Descartes proposed that man is a complex machine (with a soul). From then and onward physicists and engineers applied their concepts to handle complexity. Newton applied his “laws” to the real world. Then came Laplace's clockwork universe, which despite its immenseness could be generated from some simple laws. Yet the artificial world supporting us and our culture became more and more complex. Suddenly we realized that the weather is essentially unpredictable and found relief in the theory of chaos and its butterfly effect. Ignoring the fact that real butterflies do not initiate hurricanes. Nevertheless life’s complexity was explained by its terms.

The computer provided a mechanistic explanation of our brain. And then came the Internet, which is more complex than any computer and inspired the authors to tackle life’s complexity. Although “Chaos, fractals, random graphs and power laws inspire a popular view of complexity . . . . A different, more rewarding take on complexity focuses on organization, protocols and architecture” . . . . “So biologists can learn from engineering. The Internet is an obvious example of how a protocol-based architecture facilitates evolution and robustness.” The authors conclude:” All life and advanced technologies rely on protocol-based architectures.”

Indeed the Internet is protocol driven, yet what about the stock exchange with its internet dependency, is it also a protocol based complex system? If it were I might devote my time to search for a protocol to make me rich. Life is far more complex than the stock exchange. And yet the authors want us believe that: “All life and advanced technologies rely on protocol-based architectures.” Advanced technologies, yes, but not life! There is a limit to the complexity of protocol based systems and since life is not protocol based it is far more complex. In order to progress the authors and engineers ought to investigate how life’s complexity emerges without relying on protocols.

Why not turn our attention to a simple two CA system called proliferon, and ask the authors to define protocols that control its behavior.


1 John Doyle & Marie Csete
Rules of engagement
Nature 446, 860 (19 April 2007)

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