A work of art even greater than 'Cats': the human body

What is "art" to one person can be another's bête noire . Lucian Freud, now painting a portrait of the Queen, once refused a request from Andrew Lloyd Webber to paint his wife, and later complained that Lloyd Webber "threatened" him "with the offer of free tickets to his shows". Many people, of course, regard these shows as splendid and entertaining pieces. So, some may see it as courageous for the developmental biologist Enrico Coen to invoke "art" in The Art of Genes . This book attempts to understand how it is that genes go about producing the bodies in which they reside. What has art got to do with this?

A central question of developmental biology is how our cells, all of which carry precisely the same set of genetic information, can produce a body made of things as different as teeth, eyes, kidneys, bones and blood. A given cell cannot possibly know in advance where in the body it will find itself during development. Coen invokes the metaphor of an artist to solve this problem. Artists, he suggests, have no fixed plan for their finished product but rather continually adjust their creation as they progress and in response to what they see on the canvas. Some may cavil at this: even the great masters used cartoons. But Coen is insistent: what typifies art is the lack of a clear separation between the plan and its execution.

Development of bodies follows a similar course, in Coen's view. The environment of a gene varies locally - in terms of the gradients of various gene products at the site of development - and globally, owing to variable environmental conditions outside the developing body. If cells respond to environmental cues, then their fates are not written in some fixed plan (the contents of their genes).

Respond they do. Some cells migrate to the head and become head cells because they sense a local gradient in a messenger protein. Other cells become teeth within the head again by sensing local cues, and yet other cells adopt different roles in response to different environmental factors.Hence the idea of the gene- body as an artist, interpreting the landscape and adjusting the painting as it goes. One need look no further than the awful teratogenic effects of some drugs to appreciate the delicate role of the environment in development.

A subtly different perspective on development arises from evolutionary biology. Rather than watching what goes on in cells, the evolutionary biologist sees whole bodies living, reproducing and dying. Those better at living generally reproduce more, and in this way the collection of genes that combine to build our bodies gets honed to be reliable and reasonably efficient. Most organisms of a given type will grow up to look more or less the same, live more or less the same length of time, leave more or less the same number of offspring, and so on. The differences among individuals are typically swamped by the differences between species: no one I know looks even remotely like a chimpanzee despite the fact that we share about 98 per cent of our genes with them. If development is about "art" then most developmental artists of the same species have the same artistic style.

There is even a way to get genes to "anticipate" environmental variation. "Norms of reaction" describe the trajectories of developmental outcomes when genes are exposed to environments of varying quality or characteristics. They describe, for example, why you grow to be bigger when you are fed more in youth: children are not, in general, taller than their parents because of genetic differences. Genes specifying norms of reaction can be favoured by natural selection so long as the range of environmental conditions a gene may encounter is fairly predictable.

Perhaps these are two sides of the same coin. The difference, however, is that the artist metaphor inescapably calls forth the idea of an artist; someone who may lack an overall plan and adjusts the picture as it develops, but who is none the less in charge and making decisions about the whole canvas. In contrast, the almost incomprehensible feature of development is that no one and nothing is in charge of this most complex and bewildering set of processes. It just happens.

Coen knows this and his book gives a refreshingly clear account of how organisms make themselves from the ground up. His own evident fascination with painters means that artists from the Byzantine iconographers to Magritte and Picasso find their way into his pages, always in service of some intriguing feature of development. There is an art to understanding how organisms develop from a single cell, and scientists such as Coen are on the verge of becoming masters.

Mark Pagel is in the school of animal and microbial science, University of Reading.