BNMC Seminar -- Rules of engagement:  Architecture, robustness and evolvability

John Doyle
John G. Braun Professor of CDS, EE, and BE
Caltech

Biological systems are robust and evolvable in the face of even large changes in environment and system components, yet can simultaneously be extremely fragile to small perturbations. Such universally robust yet fragile (RYF) complexity is found wherever we look. The amazing evolution of microbes into humans (robustness of lineages on long timescales) is punctuated by mass extinctions (extreme fragility). Diabetes, obesity, cancer and autoimmune diseases are side-effects of biological control and compensatory mechanisms so robust as to normally go unnoticed. RYF complexity is not confined to biology. The complexity of technology is exploding around us, but in ways that remain largely hidden.  Modern institutions and technologies facilitate robustness and accelerate evolution, but enable catastrophes on a scale unimaginable without them (from network and market crashes to war, epidemics, and global warming). Understanding RYF means understanding architecture — the most universal, high-level, persistent elements of organization — and protocols. Protocols define how diverse modules interact, and architecture defines how sets of protocols are organized.

Insights into the architectural and organizational principles of networked systems can be drawn from three converging research themes.  1) With molecular biology’s description of components and growing attention to systems biology, the organizational principles of biological networks are becoming increasingly apparent.  Biologists are articulating richly detailed explanations of biological complexity, robustness, and evolvability that point to universal principles.  2) Advanced technology’s complexity is now approaching biology’s. While the components differ, there is striking convergence at the network level of architecture and the role of layering, protocols, and feedback control in structuring complex multiscale modularity. New theories of the Internet and related networking technologies have led to test and deployment of new protocols for high performance networking.  3) A new mathematical framework for the study of complex networks suggests that this apparent network-level evolutionary convergence within/between biology/technology is not accidental, but follows necessarily from the universal system requirements to be efficient, adaptive, evolvable and robust to perturbations in their environment and component parts.