The Swerve: How the Renaissance Began, By Stephen Greenblatt

In Primo Levi's personal anthology of his favourite writings, The Search for Roots, is a specialist paper on how to prevent cockroach attack on industrial varnishes. Levi's "roots" were only part literary: by profession he was an industrial chemist. Of the 30 authors he chose, eight were scientists or prototype scientists. Among them was the Latin poet Lucretius, whose book-length philosophic poem On the Nature of Things Levi considered a luminous celebration of the mysteries of the natural world. The deeper Levi read into the poem, he said, the more he was awed by its grandeur and uncanny modernity. In the "poet-researcher" Lucretius, he found an alternative theology that recognised no God, but which anticipated a large part of contemporary science.

With strange prescience, Lucretius wrote of how rivers, foliage and pastures are transformed into cattle, and how these cattle are consumed by humans, who in turn provide sustenance for predators. Lucretius did not know it, but he was writing about the quintessential atom of life - carbon - at a time when atomic theory did not exist. Atoms are the sole "building blocks" of the universe, Lucretius believed. When we die, our "atoms" dematerialise. The gods may exist, but they are unmindful of us mortals.

For Stephen Greenblatt, the distinguished Renaissance scholar, Lucretius is the unsung influence on modern thought. In The Swerve he tells how Lucretius came to galvanise the Renaissance and the revival of scientific humanism. On the Nature of Things became "modern" when a scholar and papal scribe, Poggio Bracciolini, chanced on the last surviving manuscript of the poem during a "book-hunting tour" of German monasteries in 1417. Bracciolini's discovery constituted a "swerve" – an unforeseen deviation – from the path to oblivion along which Lucretius seemed to be travelling. The poem was translated and disseminated widely.

Thanks to the poem's reappearance, European civilisation was made to "swerve" away from the religiosity of the Christian Middle Ages into a worldview that we recognise as our irreligious own. Souls do not exist, according to Lucretius; there is no afterlife: live, then, for the present moment. From this godless materialism it was a short step, argues Greenblatt, to the "devastating disbelief" expressed in Diderot, Hume and other Enlightenment figures.

Certainly Lucretius was ahead of his time. Girolamo Savonarola, the firebrand church reformer of Renaissance Florence, fulminated against Lucretius and his theory of atoms, which seemed to militate against the preacher's blood-and-brimstone Christian absolutism. Conceivably, On the Nature of Things was among the "heretical" publications Savonarola and his followers gathered up and set ablaze in a giant "bonfire of the vanities". Like a biblical prophet, says Greenblatt, Savonarola saw himself as a chastiser of godless thought come to cauterise the human heart of sin. On the Nature of Things had only recently been returned to circulation by Bracciolini, and so it was bound to incur Savonarola's spiritual ferocity.

For all his marvellous verve and scholarship, Greenblatt makes exaggerated claims for Lucretius. On the Nature of Things may have been forward-looking and audacious, but does it really provide "an astonishingly convincing account of the way things actually are"? Bracciolini, with no less hyperbole, is described as a "midwife to modernity". The poem - of 7400 lines - does impress by its intellectual ambition and theories of the physical world. But whether it changed the course of humankind is another matter.

It may be more fruitful to look elsewhere for Lucretian influences. Two thousand years before Richard Dawkins or Stephen Jay Gould, Lucretius had sought to make atheistic "science" accessible to the layman. The French call it haute vulgarisation – high-class popularisation. Lucretius's poem, a lapidary integration of literature and atom theory, foreshadowed this popularising trend. Thus Levi, while researching his literary-scientific memoir The Periodic Table, often consulted Lucretius, and sometimes even borrowed from him. The "Carbon" chapter is a blatantly Lucretian fable about the infinitude of matter.

Four centuries earlier, the philosopher Montaigne included almost a hundred direct quotations from Lucretius in his Essays. The adapted material was not quite plagiarism, but secret praise, rather, for the Latin poet who formed the bedrock of just one man's sceptical worldview.

Ian Thomson's biography of Primo Levi is published by Vintage