Our craving for heroes has created images of scientific supermen who single-handedly changed our lives for the better. But, argues John Waller, we should be looking at the wider picture.

In the BBC's chart of Great Britons, scientists clock up almost as many places as politicians and pop stars combined. Given the increasing popular mistrust of all things scientific, this might seem surprising. But the explanation lies in the kinds of candidate put forward. If we take the three placed in the top 20, Charles Darwin, Isaac Newton and Alexander Fleming, there are two who have dramatically increased our understanding of how the world works and a third who is believed to have saved millions of lives. What is less obvious, however, is that all three men owe their places in the ranking less to strict historical truth than to the human craving for heroes.

Over the past three decades, the history of science has been subject to rigorous re-examination. Virtually everywhere that historians have cast their critical gaze, the standard heroes have begun to seem far more flawed and complex.

Andrew Marr's recent advocacy of Darwin's claim to the BBC's top spot is but one case in point. Before Darwin, explained Marr, ideas about the natural world were governed by ignorance and superstition. The evidence for evolution lay all around, but the intellectual stranglehold of the church was too strong for its meaning to be discerned.

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But this account is largely myth. For instance, to establish Darwin's revolutionary credentials, Marr says that before the On the Origin of Species (1859), most people still accepted Bishop Ussher's famous calculation that the Earth came into being some time in the afternoon on Sunday October 23 4004BC. Yet this is simply untrue.

Even the dog-collared naturalists with whom Darwin hob-nobbed at Cambridge University before embarking on the Beagle voyage scoffed at Ussher's efforts. Fossilised sea creatures found in mountain ranges and evidence that temperate regions had once been bathed in tropical sun had convinced most British intellectuals by the late 1700s that the Earth was unimaginably old.

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Nor was Darwin even remotely original in speculating about the possibility of human evolution. Numerous precursors, including his own grandfather, had earlier speculated that species change over time. At Edinburgh University during the 1820s, a radical young biologist called Robert Grant delighted in explaining to a rather innocent Charles Darwin the evolutionary theories of the Frenchman Jean Baptiste Lamarck. Yet Grant and Lamarck are usually ignored or, when they aren't, they are described as the nearly-guys who got it hopelessly wrong where Darwin so emphatically got it right. Lamarck argued that evolution is driven by the inheritance of acquired characteristics (the notion that giraffes have long necks because over many generations their ancestors had been straining to reach higher leaves). Darwin's idea of natural selection, which he hit on in September 1838, put clear water between himself and Lamarck. Yet Darwin would always remain steeped in Lamarckian tradition.

Thus, he never doubted that the inheritance of acquired characteristics was a necessary adjunct to evolution by natural selection. Indeed, with each successive edition of the On the Origin of Species this mechanism was accorded ever greater importance. And, as he lost confidence in natural selection, so did his scientific colleagues. While the notion of human evolution managed to gain wide currency by the end of the Victorian age, the idea of natural selection made hardly any impression at all. For perfectly valid reasons, many evolutionists found Lamarckism a far more congenial and intellectually credible theory until the 1920s.

The Newton myth contains many of the same tropes. There is no doubting Newton's intellectual virtuosity. But modern scholarship shows that Newton spent far more time cooped up in his suite of rooms in Cambridge investigating alchemy and developing heretical religious beliefs than he did working out gravitational theory. It is also clear that he owed considerable, unacknowledged debts to his fellow natural philosophers. Even the story of the falling apple seems to have been a self-serving invention designed to backdate his discovery of the laws of motion and thereby marginalise the major contributions made to it by Robert Hooke and Edmond Halley.

More important still is the fact that Newton didn't die having proven how the universe works. Doing the sums required to explain planetary motions is dizzyingly hard. For years, he struggled with accounting for the movements of the moon alone. And, despite helping himself to astronomer royal John Flamsteed's unpolished lunar observations, Newton passed away with the problem unsolved. Even as late as the 19th-century, mathematicians were still trying to prove that his ideas applied as much to cosmic movements as to falling apples. It was only thanks to a well-orchestrated PR campaign after his death that the hopelessly unrealistic notion that Newton furnished both theory and proof managed to get off the ground.

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Fleming, at number 20 in the BBC chart, is credited with inaugurating the revolution in curative medicine to which so many of us owe our lives. But here, too, the historical record tells a different story. Fleming did discover penicillin in 1928 after a rogue spore landed in an unwashed Petri dish. It is also true that he decided that he had found the "magic bullet" for which he had spent years searching. But Fleming's notebooks and published papers make it clear that soon after he began his penicillin research, he abandoned it as clinically unpromising.

Fleming later claimed this was because he'd been let down by a series of sloppy and defeatist biochemists. This is nonsense. The few biochemists who did try to investigate penicillin during the 1930s got neither help nor encouragement from Fleming.

In the event, the transformation of his chance discovery into a brilliant antibacterial weapon owed almost everything to a team of biochemists working under the Australian Howard Florey at Oxford University in the early 1940s. By the time Florey's men got going, Fleming was entirely out of the picture; at least one member of the team thought he was dead. But once they had proven penicillin's vast clinical potential, Fleming saw the chance he had let slip through his fingers. Fortunately for him, the assistance of his hospital bosses and a sympathetic newspaper baron enabled him to create the myth that gives him the giant's share of a reputational gold mine.

These reappraisals might seem like pointless hero-bashing, but I think they enrich our understanding of science. Discard the popular mythology and it becomes clear that scientific merit is only one of many factors influencing whether or not an individual achieves posthumous greatness. Thus, Fleming's celebrity was due largely to the funding needs of the hospital he worked for and Britain's unexceptional appetite for home-grown heroes. Darwin eventually achieved stardom because what we now know as Mendelian genetics came to his rescue in the early 1900s. Finally, for all of Newton's brilliance, his modern-day reputation stands on the shoulders of those who came after him and supplied the proof for his theories.

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The moral from these revisionist histories seems clear. However attractive it may be, we should abandon the simplistic notion of the history of science being peopled by begrudging Lilliputians whose small horizons are forcefully transformed by occasional Gullivers. Instead, we should look on science with the acumen of the successful football manager. A clear-eyed assessment of lots of individual contributions makes far more sense than simply heaping praise on the guy we've been told scored the all-important goal.

John C. Waller is a research fellow at the Wellcome Trust Centre for the History of Medicine, University College London and author of Fabulous Science: Fact and Fiction in the History of Scientific Discovery , OUP, 2002. Isaac Newton is the focus of tonight's Great Britons programme on BBC2, 9pm.

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