How to wake up in the morning without an alarm clock

Can you do the alarm trick? Set the clock. Take a good look at the time before you sleep. Wake five minutes before the noise. I can, so there must be a timepiece in me as well as by my bedside. Some regular chemical cycle, some combination of proteins must tick away the seconds and generate a signal that reaches my slumbering brain. A modern biologist faced with something as clever but commonplace as this wants to know exactly how it works. Which molecules are involved? Which genes? And current work on the fruit fly is yielding answers to these and similar questions about links between genes, brains and actions.

The American science writer Jonathan Weiner, whose last book, the marvellous The Beak of the Finch , won a Pulitzer prize, here gives us a successor that is also built around the career of one scientist and his students. His story of the fly genes focuses on the fascinating figure of Seymour Benzer, one of the physicists who helped found molecular biology by dissecting the DNA of the bacterial viruses known as phages.

Benzer, like others, had turned to phages because the fruit flies that were the favourite organism of geneticists for the first half of the 20th century were too complicated for work inside individual genes. By the mid-1960s, though, he had had enough of phages, and his thoughts turned again to creatures with cells, organs, nervous systems. He had shown how to map the fine structure of a gene - but how were these molecular messages related to higher levels of the organism?

For answers, he went back to the fly, and to certain things that flies can do but bacteriophages cannot. They move towards the light. They mate. They can learn to avoid unpleasant experiences. And they get up in the morning.

Gradually, Benzer and his students found ways to measure all these things experimentally, and isolated mutants for each one. Flies with no sense of time or direction, aberrant sex drives, or that were unable to learn, all had altered genes that could be located on the already well-mapped chromosomes of the insect. The ensuing research programme vindicated Benzer's assumption that "behaviour is the way the genome interacts with the outside world".

It is a well-told tale, eased along by a nicely lubricated style. Almost too well-told perhaps. For although Weiner often touches on the obvious questions about how dissecting the fly's genes relates to the human condition, he could pose some of them more sharply. He tells us that human studies get over-interpreted and over-reported in the press, yet the small manoeuvres of the fruit fly are rendered throughout the book with a finely calculated anthropomorphism.

But this suggests that there will be a simple progression from these studies to an understanding of human action, that the lords of the fly are identifying the elementary particles of behaviour from which all else is composed. The kind of elision this promotes is shown by the switch in my proof copy from Weiner's subtitle - "A Great Biologist and His Quest for the Origins of Behaviour" - (my emphasis) to Faber's cover line - "The Story of Genes and Behaviour".

The problem is not even with the three key words of the title - time, love, memory - but with the umbrella term, behaviour. The fact that it makes sense to say that flies exhibit behaviour does not imply that we can understand human behaviour in the same way. Flies, for example, cannot behave badly. Nor, I take it, can they be unkind, moody, demotivated, or guilt-stricken. They have behaviour, but no conduct.

Weiner knows this perfectly well, and at the end of the book waxes lyrical about the mysteries of consciousness and the

difficulty of saying anything sensible about the constraints set by the genes that shape human minds. But he waits a long while to dispel the impression that Benzer's research programme, with its brilliant successes in

unravelling the minutiae of the fly's dealings with the world, leads naturally to an understanding of our own.

With that caveat, this is a fine piece of popular writing and infinitely preferable to any number of breathless books about gay genes, DNA sequences for happiness, or other versions of biology as destiny.

Jon Turney is senior lecturer in science communication, University College London.