What is life? So asked the distinguished physicist Erwin Schroedinger in his famous lecture at Trinity College Dublin in 1943. Now, after the full mapping of the human genome has yielded a code of three billion letters, we are still far from a satisfactory answer to this question.

The reductionist approach of molecular biology has proved itself immensely powerful. But DNA isn't life. It doesn't even leave the nucleus of the cell. A whole army of proteins is needed to unpack, edit, and execute the information it contains. Without this apparatus, DNA is but an inert database, full of errors and repetitions. To grasp the nature of life, argues the world renowned physiologist Denis Noble, we must move away from our obsession with genes alone. We must look not at one level, but at the interaction of processes at various levels, from the realm of systems biology, a field that has been growing in strength in the past decade, pioneered by distinguished biologists such as Sydney Brenner. Noble, himself one of the founders of this field, argues that far from being a vague, unsatisfactory, and even faintly mystical holistic view, modern systems biology can be just as mathematically rigorous and exact as the reductionist approach that has led to the vast knowledge amassed by molecular biology in the past fifty years. And it may be the view we need to adopt to gain a deeper understanding of the nature of life.

In this elegant essay, Noble sets out this alternative to the gene's eye view which has reaped so many rewards; a radical switch of perception in which genes are prisoners and the organism itself is a complex system of many interacting levels. And life emerges as a process, the ebb and flow of activity in the intricate web of connections, full of feedback between gene, protein, cell, organ, body and environment.

It is a kind of music - a metaphor that is woven throughout this personal and deeply lyrical work. Drawing on his experiences in his research on the heartbeat, and on evolutionary biology, development, medicine, philosophy, linguistics, and Chinese culture, Noble presents us with a profound and very modern reflection on the nature of life.

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