Life: make it up as you go

It is refreshing to read a book about evolution that does not take an ultra-reductionist approach that everything is determined by genes. I for one am convinced that life, too, shapes organisms. Natural selection acts primarily upon the phenotype rather than the genotype. Although Lifelines makes a strong case against what Steven Rose calls an ultra-Darwinist approach to life, it is not an argument against either evolution or natural selection, rather it strengthens the case for both by presenting a much more balanced case.

Authors such as Richard Dawkins and Daniel Dennett have received much publicity for their claims that everything is determined by DNA. To Rose, this "vulgar biological determinism and cheap ultra-Darwinism I increasingly seems to pervade everything". He argues that the individual gene is not the only level at which selection occurs and that natural selection is not the only force driving evolutionary change. Further, organisms are not mere passive responders to selective forces but active players in their own destiny.

Rose writes: "Because genes are in genomes are in developing cells are in muticellular organisms, the relationship between gene A and phenotype A is non-linear, and each level of organisation, and indeed each moment during the developing trajectory of an individual organism's lifeline, offers an opportunity for selection to act." In other words, selection is at work between genes, between cells and between populations. It also operates strongly in communities between the different species that interact competitively or cooperatively.

Central to Rose's theme is autopoesis: the property of all life to build, maintain and preserve itself. Organisms are not passive individuals waiting to be battered about by their environment; they are actively working to choose and transform their environments to their advantage. There is a certain amount of self-determinism, whether it be at the level of cell, organism or lifeline. There is a certain freedom in nature for a single-celled organism to leave a depleted food source for a rich one, or a growing troupe of axons from the retina of a cat to seek, find and modify their target neurons in the lateral geniculate.

Also central to the argument is a fable that Rose introduces in the early pages and refers back to several times. Five biologists are having a picnic beside a pond when they see a frog leap into the water in reaction to the presence of a snake in a nearby tree. Each of the biologists -a physiologist, an animal behaviourist, a developmentalist, an evolutionist and a reductionist molecular biologist -Jinterprets the event according to his own discipline and the level at which he studies life, be it the ecosystem, the molecular, the developmental or the evolutionary approach. Rose argues that each approach contributes to science, and these different accounts cannot be collapsed into the one true explanation in which the event becomes nothing but a result of the molecular make-up acting on a genetic imperative.

This book calls for an integration of the facts from each discipline and argues that no single fact or discipline, not even the genetic code, provides all the answers. The phenomena of life in an organism are complex and richly interconnected, and it is poor science to oversimplify them. The reductionist looks for the gene that causes aggression, alcoholism and every other aspect of human behaviour. The more holistic biologist also relates such traits to the environment and development of the individual. To reduce social concerns to just genetics and biochemistry is poor science and likely to lead to poor cures for the problem. Rose makes a strong case for the more holistic approach in addressing social issues.

Although it is written mainly with examples from human biology, as would be expected from a neuroscientist, Lifelines is essential reading for anyone interested in biology and evolution, especially those tempted by the reductionists' plausible arguments. Rose wanders far from human biology and the philosophy of biology into many other forms of life: from the biochemistry of the leaping frog, the Fibonacci series in pine-cones and Shasta daisies, to the structure of the honeycomb and the origin of life itself. Rose is at his most controversial in discussing origins, arguing that life did not begin with nucleic acid, rather that self-replicating DNA and RNA appeared later, once there were cells and organisms ready to receive and utilise them.

Apart from this more radical idea, Lifelines presents life in an integrated, interactive way, showing that we are much more than the configuration of our DNA. As the author says: "The organism rather than the gene is at the centre of life." Although we do derive many characteristics from our genetic inheritance, there is also a freedom in life that allows us to shape our destiny. As organisms respond to their environment, they change it for themselves and future generations.

Sir Ghillean Prance is director, Royal Botanic Gardens, Kew.