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Robustness and Evolvability in Living Systems: (Princeton Studies in Complexity)

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Living organisms are both robust and evolvable -- two properties that could seem to contradict one another. They are robust in the sense that they can withstand, both as individuals and as lineages, changes in their environment, changes that are sometimes very large. At the same time they can evolve, which means that they leave descendants that remain well adapted to their environment through many generations. Without these two properties life could not have survived from its beginnings billions of years ago to the present, despite huge changes in the earth during that time, such as the change from a reducing atmosphere to the current oxidizing atmosphere, with concentrations of oxygen in the air and the oceans that would be lethal for all of the early organisms.

As Andreas Wagner explains in this important book, the two properties of robustness and evolvability exist at many different levels: the genetic code, the structures of nucleic acids and proteins, metabolism, body plans, and so on. He goes on to analyse each of these and others in different chapters. In each chapter he sets out to answer the same two questions: what characteristic is robust? what is it robust to? For example, the three-dimensional structure of a protein, necessary for maintaining its function, is robust to changes in its aminoacid sequence.

Wagner was one of the originators of the "small world" view of metabolism -- the finding that the number of steps needed to go from any metabolite to any other is much smaller than one might guess without doing the analysis -- and has recent research publications in most of the topics he discusses in his book. As a result he has produced an expert account of robustness that anyone interested in this important topic needs to be familiar with.

This is a well written monograph on two fundamental but often contradictory properties of living entities: evolvability and robustness. The text gives multiple examples in which a system is robust (sort of dynamically stable) in one respect while retains a window of opportunities for change in another respect. This book is potentially interesting for traditional scientists ("reductionists" by habit) as well as holistically motivated modern biologists. I believe it is so well written and organized that it could become a must read for anyone interested in systems biology, whatever the latter term means today.
Perhaps a word of caution should be issued here for the readers who intend to learn about systems thinking regarding living matter. The assumption of very specific characteristics that a system is robust to is oversimplification of real problems in life sciences. So is a choice of specific properties according to which the system could evolve. The real living entities are complex in a sense that a very enumeration of their characteristics is a hopeless problem in itself. In contrast, the chemical models of these entities can be described in terms of selected (enumerated) characteristics. From this point of view this book is not really about living systems but about their very specific chemical models. Having said that, I hasten to state again that the book is a great reading and should be read.