In the 1850s, and deep in his research for On the Origin of Species, Charles Darwin and his wife, Emma, gave orders for their daughter’s cat to be killed. Puss had recently mauled one of the fancy pigeons with which Darwin had been trying out his own theories of selective breeding. No one had warned little Etty Darwin about her pet’s fate, and as an old woman she declared that the trauma of discovering her parents’ treachery still rankled. Here, in a nutshell, is the kind of anecdote on which AN Wilson’s “revisionary” biography of Darwin depends, one that dramatises the great man of science as a monster of ruthless self-interest, an assassin in a nightmare land of kill-or-be-killed. The only way that the story could be bettered from Wilson’s point of view is if he could show Darwin actually strangling the cat with his bare hands.

What Wilson is engaged in here, then, is not just a demolition of Darwin’s science, which he maintains is mostly bogus and outmoded, but an assassination of the man’s moral character. Darwin, Wilson contends, was not the nervy but benign magus of Down House, labouring patiently for decades in rural Kent to unlock the origins of human life for the benefit of all mankind. He was actually an egotist with an unfailing eye for “the main chance”, determined to go down in history as the greatest scientist of all time. According to Wilson’s long charge sheet, Darwin routinely stole ideas, couldn’t be bothered to go to family funerals and wasn’t keen on sex, despite having 10 children (some of whom were “notably plain”). Despite dying seven years before Hitler was born, he apparently paved the way for the Nazis’ love affair with eugenics. To cap it all, his unsavoury insistence of having a “privy” in the corner of his study meant that he probably smelled of his own poo.

Wilson concedes that Darwin 'was among the foremost experts on the earthworm' but not much else. Specifically, the big picture stuff was beyond him

First, let’s take the science. Wilson concedes with a smirk that Darwin “was among the foremost experts on the earthworm” but not much else. Specifically, the big picture stuff was beyond him, which is why he gobbled up other people’s theories about evolution, including those of his grandfather Dr Erasmus Darwin, and then passed them off as his own. Indeed, Darwin-as-plagiarist is one of the chief poison darts in Wilson’s argument. What actually happened, of course, was that Darwin absorbed the hints and hypotheses of an earlier generation of science writers, including those of his grandfather, and embarked on a painstaking programme of data-gathering that allowed him to substantiate what had previously been merely a widely held hunch. That there remained gaps, dead ends and errors in his narrative account of how life unfolded on earth over multi-millennia was something Darwin was always quick to acknowledge. It was in response to the questions and corrections that flooded into Down House from around the world that he continued to modify his arguments. This, one might think, is what scientists do, especially ones who are committed to the concept of evolution, the slow adjustments of shape and form over time. For Wilson, however, Darwin’s constant need to revise his published work is evidence of nothing more than the narcissist’s terror of being caught in the wrong.

Although Wilson will just about allow On the Origin of Species a credible place in the history of science, The Descent of Man, published 12 years later in 1871, is his holy terror. It was in this book, Wilson suggests, that Darwin finally came clean about his view of the natural world, which crucially now included the human race alongside fancy pigeons and pet cats, as a dog-eat-dog frenzy, where only the fittest survive and everyone else ends up as lunch. It was a terrifying vision, unless you happened to be a member of the emergent upper-middle classes to which Darwin and his Wedgwood cousins belonged. For this happy crew, whose income came mainly from mature investments rather than directly from manufacturing or agriculture, it was consoling to believe that prosperity and pre-eminence were the just rewards of intellect and energy, while poverty was a kind of moral failure. As far as Wilson is concerned, what Darwin does in the aptly named The Descent of Man is to provide a charter for amoral greed, whereby “people like us” carry on despoiling British society, and increasingly the rest of the world, with nothing more than a slight murmur of regret about how unfair life is.

Jaunty pleasure in ruffling feathers … AN Wilson outside the British Library in 2008. Photograph: Antonio Olmos/The Observer

None of this is remotely new. For decades, historians of science have acknowledged that Darwin’s natural world bears a striking resemblance to mid-Victorian Britain, minus the antimacassars and the workhouse. But to argue, as Wilson does, that Darwin positively relished the principle of vicious individualism over mutuality and collaboration simply isn’t true. His most famous motif, the one that everyone remembers because it leaps off the page with such unforced joy, is that of the tangled bank. Based on his daily observations of a stretch of land near his home, Darwin describes a buzzing ecosystem that is home to plants, birds and insects “all dependent on each other”. Here, he implies, is a microcosm for how we too might imagine our lives.

Most beastly of all, though, is Wilson’s almost-claim that Darwin was secretly sympathetic to slavery. By a series of elisions as slithery as any he ascribes to his subject, he manages to suggest that, if forced to answer the question posed by the enchained black man on the famous abolitionist medallion, “Am I not a man and a brother?”, Darwin “could” have answered “in the negative”. The shock value comes from the fact that the medallion, which did so much to turn ordinary Britons against slavery in the 1790s, was made by Darwin’s grandfather, the potter Josiah Wedgwood.

To blame Darwin for being racist is like accusing Freud of not being a feminist, which is to say both blindingly obvious and slightly beside the point

It turns out that Wilson has no evidence for this egregious slur. All he can muster is the whiskery argument that, because Darwin saw black and brown people (not to mention Jews, Slavs, Celts and anyone who didn’t come from his native belt of central England) as lesser, he was a proto-eugenicist. What he actually was, however, was an Englishman with the usual prejudices of his time. To blame Darwin for being racist is like accusing Freud of not being a feminist, which is to say both blindingly obvious and slightly beside the point.

Instead of subtitling this book “Victorian Mythmaker”, Wilson might have more accurately called it “J’Accuse”. For despite a few pious throat-clearings on the dust jacket to the contrary, he has no interest in balance, no desire to be nice about the man whom he blames for pretty much everything that went wrong in the 20th century, from totalitarianism to the decline of organised religion.

Still, Wilson being Wilson, there’s no mistaking the jaunty pleasure he gets from this exercise, and the fun he has in knowing that he is going to ruffle as many feathers as little Etty Darwin’s cat did when it stole into the loft at Down House and started snacking on a particularly juicy pigeon.

• Kathryn Hughes’s Victorians Undone is published by Fourth Estate. Charles Darwin: Victorian Mythmaker is published by John Murray. To order a copy for £21.25 (RRP £25) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.