How can a chemical system act purposefully? Bridging between life and non-life

One of life's most striking characteristics is its purposeful (teleonomic) character, a character already evident at the simplest level of life - a bacterial cell. But how can a bacterial cell, effectively an aqueous solution of an assembly of biornolecules and molecular aggregates within a membrane (that is itself a macromolecular aggregate), act purposefully? In this review, we discuss this fundamental question by showing that the somewhat vague concept of purpose can be given precise physicochernical characterization, and can be shown to derive directly from the powerful kinetic character of the replication reaction. At the heart of our kinetic model is the idea that the stability that governs replicating systems is a dynamic kinetic stability, one that is distinctly different to the thermodynamic stability that dominates the inanimate world. Accordingly, living systems constitute a kinetic state of matter as opposed to the thermodynamic states that dominate the inanimate world. Thus, the model is able to unite animate and inanimate within a single conceptual framework, yet is able to account for life's unique characteristics, amongst them its purposeful character. As part of that unification, it is demonstrated that key Darwinian concepts are special examples of more general chemical concepts. Implications of the model with regard to the possible synthesis of living systems are discussed. Copyright (c) 2008 John Wiley & Sons, Ltd.