‘From Adam has sprung one mass of sinners and godless men,” wrote St Augustine, arguably the key architect of the Christian doctrine of original sin. The notion that babies are born with this indelible stain, the residue of Adam’s fall in Eden, can seem one of the most pernicious features of Christian dogma. But as Guy Leschziner argues in Seven Deadly Sins, we could interpret Augustine’s austere judgment as an acknowledgment that we are inherently inclined to do things we shouldn’t. The catalogue of seven direst vices first adduced by Tertullian and immortalised in Dante’s Divine Comedy – pride, greed, wrath, envy, lust, gluttony and sloth – may seem arbitrary, but we can all recognise aspects of them in ourselves.

Leschziner, a consultant neurologist at Guy’s Hospital in London, explores the physiological and psychological roots of these “failings” and argues that, in mild degree, all might be considered not just universal but necessary human attributes. The goal, he implies, is not to renounce them but to align our natural impulses with the demands of living healthily and productively in society. Seven Deadly Sins takes the case-study format pioneered by Oliver Sacks in using dysfunction to explore the neurological origins of behaviour. It is a profoundly humane book, occasionally compromised by excessive clinical detail and perhaps more so by its lack of wider context.

Like Sacks, Leschziner writes with great empathy and compassion about patients facing often heartbreaking situations. Rhett has witnessed his wife, Becky (“the sweetest girl I’d ever met”), turned acutely irritable as well as near-catatonically apathetic by Huntington’s disease (sloth). An undiagnosed neurological condition lies at the root of Sarah’s conviction that her husband is cheating on her (envy). Easy-going Jono experiences outbursts of violent aggression related to his epilepsy (wrath).

Seven Deadly Sins effectively and usefully counters the idea that deviations from norms of, say, anger, appetite, or motivation stem from differences between brains that are “healthy” or “ill”. Equally, Leschziner challenges the common view that only problems originating in bodily disfunction are “real” while ones that seem essentially psychological are imagined or made up. “These views taint clinical medicine and wider society”, he writes. Surprisingly, he does not relate that to long covid, which has highlighted the prejudice at the same time as problematising the distinction.

Yet by examining each “sin” through the lens of pathological mental disregulation caused by injury, trauma, or disease, Leschziner pulls the focus away from the regular bounds of human behaviour. Episodes of uncontrollable anger caused by epilepsy or brain haemorrhage are tragic but do not illuminate why those of us lucky enough to escape such conditions might feel surges of rage.

Moreover, Leschziner locates causation primarily in the makeup of the person. Take “gluttony”, which he examines largely in relation to genetic malfunctions in the brain’s satiation signalling. As an explanation of why obesity may be a neurological issue unfairly labelled as a moral failing, the discussion is timely and important. But he omits the link between obesity and socioeconomic disadvantage. It would be all too easy to suppose from Seven Deadly Sins that predisposition to these potentially problematic behaviours is a lottery dictated by genetics combined with unpredictable slings and arrows of accident and illness. Yet socioeconomic circumstances are often highly pertinent – not least because these can affect the chance of illness, injury, or other causative factors in the first place. In the post-pandemic era, there can be no disputing the extent to which health is a political as well as a physiological issue.

Leschziner also sometimes subscribes to a simplistic aetiology rooted in evolutionary psychology whereby our personal genomes (he repeatedly misuses the term “genetic code”) are blueprints (“the essence of us”) that dictate traits. To the extent that this is correct, it tends to produce merely truisms: we need a bit of lust to pass on our genes, a bit of gluttony to survive, a bit of envy to defend procreative partnerships, and so on. But much of the complexity and diversity of human behaviour comes from the fact that brains aren’t computers governed by genes but can innovate, adapt and respond in open-ended ways that may or may not confer long-term advantage.

Which brings us back to Augustine. His writings were partly a response to the heretical view of the theologian Pelagius that humankind can only be truly virtuous if we have the capacity for free will to redeem ourselves. Leschziner concludes with a chapter on free will that reflects the tension evident throughout the book. “Our opinions, our actions, our personalities – essentially all that makes us human – are simply a function of neurones, or neurotransmitters, of trillions of synapses”, he writes, before confessing that this deterministic view makes him squirm intuitively. The problem lies in that “simply”; one could equally say that our behaviour is “simply” a product of atoms in motion. Focusing on case studies where the complex higher-level processes of volition have been compromised by physiological breakdown can end up obscuring both our capacity for self-determination, and the way our cultures and social circumstances constrain or diminish it.