Francis Crick, by Matt Ridley

As a boy, Francis Crick was "haunted by a fear that by the time he grew up everything would have been discovered". Born in 1916, the son of a Northampton shoe manufacturer, he was no prodigy and "for the first 35 years of his life he was, in achievement... unremarkable". Matt Ridley's biography charts Crick's path from "middle-class mediocrity" to one of the most influential scientists of the century.

At university (where he studied physics) and during wartime work on magnetic mines, Crick was more likely to attract attention for his high-pitched laugh than his scientific insights. In 1946, impatient to discover something before there was nothing left, Crick began looking for a scientific mystery to solve. He narrowed the field down to either the secret of life or the secret of consciousness. First he decided to focus his physicist's mind on life. Later, at the end of his career, he turned to the problem of consciousness.

Even by the late 1940s, it was not widely accepted that genes were made of DNA. It was also not understood how genes could synthesise another structure. By 1949, Crick was investigating the molecular structure of biological systems at Cambridge's Cavendish Laboratory. His outspoken nature made him a difficult colleague. The "loudmouth with the braying laugh" thought nothing of telling his esteemed superiors, Lawrence Bragg and Max Perutz, what was wrong with their science even though everyone knew he was not much use in the laboratory. According to his daughter, he was "as dextrous as a pound of sausages".

Crick had become that rara avis in biology, a theoretician. "His method of working," said a colleague, "was to talk loudly all the time." But he had an extraordinary ability to visualise the biological world at a molecular level. It was this "combination of imagery and logic" that allowed him to gain unparalleled insights into life's mysteries.

On 17 March 1953, Crick wrote to his 12-year-old son about a "most important discovery" he had made with his young American colleague, Jim Watson: "we think we have found the basic copying mechanism by which life comes from life". Their remarkable discovery had been announced a few days earlier - in the Eagle pub in Cambridge, where they regularly ate lunch. Over a pint of bitter, Crick declared to his fellow-drinkers that they had just discovered the secret of life.

When Watson tried to describe the DNA double helix, he was reduced to mumbling "it's so beautiful... so beautiful". Though equally awe-struck, Ridley's account of the science is thankfully more eloquent. Crick and Watson were the first "to see how DNA acts as a linear digital information-storage device". The two helices could unzip and duplicate their codes: "heredity was manifest in the very structure". The words in the book of DNA formed a "universal cipher", a code for making proteins. Over the next decade, Crick explained the complex machinery of protein synthesis, and "DNA makes RNA makes protein" became the new dogma. Ridley's succinct and rounded provides a wonderful insight into the challenges and rewards of a life dedicated to probing the secrets of nature.

Peter D Smith is writing a cultural history of science and superweapons