Cathy Gere begins this wise, fascinating and original book in Tuskegee, Alabama, where a large public-health experiment was launched back in 1932. The purpose of the research was to investigate ‘untreated syphilis in the negro male’; 600 black men – 399 infected, 201 not – were persuaded to take part, in exchange for a few perks and ‘special free treatment’ for ‘bad blood’. They were subjected to plenty of tests (including crude spinal taps), but they were never given any treatment, even after 1946, when penicillin became available as an effective cure for syphilis. The whistle was blown in 1972, after which the New York Times carried an exposé and the forty-year project was closed down. Senator Edward Kennedy conducted an inquiry. Ever since, the Tuskegee experiment has stood as a monument to the evil that doctors do, inviting obligatory comparisons with Nazi medicine.

Gere, who is nothing if not courageous, sets out to show that the furore over the Tuskegee experiment was ‘not a battle between good and evil, but rather a conflict between two conceptions of the good’. She defends her analysis over the next 300 pages or so in a series of masterclasses in the art of untying conceptual knots by means of astute historical analysis.

Her first stop is the Doctors’ Trial held under US jurisdiction at Nuremberg in 1946–7, directly after the main war crimes trials. Twenty-three Nazi doctors were accused of subjecting their patients to extreme hardship in the name of medical experimentation, which often involved deliberate infection with life-threatening diseases. The chief prosecutor submitted that such procedures ‘departed from every known standard of medical ethics’, but he was brought up short when a defence lawyer brandished a copy of Life magazine from 1945, containing a photo essay celebrating an experiment in the United States that involved infecting hundreds of prisoners in Illinois with malaria. The prosecution responded by claiming that the Illinois prisoners had freely volunteered and hence that any similarities with victims of Nazi experimentation were purely coincidental. It was a blatant lie, but it enabled the court to promulgate the epoch-making principle that medical experimentation should never be conducted without informed consent from the subject.

Like everyone else, Gere recognises this principle as one of the great achievements of modern jurisprudence. She also goes along with what is now a truism of medical ethics: that the principle of informed consent signals a victory for romantic Kantians (who uphold the sanctity of individual rights regardless of the consequences) and a defeat for scientific utilitarians, who would not allow the moral squeamishness of others to stand in the way of the greatest possible benefits for the greatest possible numbers. But Gere brings a distinctive sense of history to the conversation. She reminds us that until 1947 medical research had always been conducted under the banner of utilitarianism, with doctors considering it not only their right but also their duty to prioritise the welfare of the many over the sufferings of the few, especially if the few are destitute anyway. They were overwhelmingly benevolent in their intentions, justifying their approach with conscientious profit-and-loss calculations where the units of account were not dollars or pounds but pleasure and pain. On top of that they were confident that their approach to medical ethics was confirmed by the findings of modern scientific psychology.

Edward Kennedy’s inquiry heard evidence in defence of Tuskegee from a couple of psychologists. One of these, Robert Heath, showed some home movies to prove that he had identified the ‘pathways’ for pleasure and pain that govern all human behaviour, without any need for the hypothesis of freedom: by delivering electric currents to electrodes stuck into the brains of derelict psychiatric patients, he could raise and lower their happiness level at will. Another, B F Skinner, backed him up with findings from experiments that seemed to show that all of us are slaves to the pursuit of pleasure and the avoidance of pain. There was no point in appealing to ‘freedom’, he said, because behavioural science had proved that ‘we are all controlled, all the time’. As far as they were concerned, the old utilitarian idea that natural rights are rubbish was based not only on philosophical arguments but also on experimental scientific facts.

The rest of Gere’s book traces the development of this curious utilitarian amalgam of facts and values from 17th-century neo-Epicureans all the way to 21st-century neuroeconomists and neuroscientists, who regard human beings as pleasure-maximising machines and urge us to ‘eschew the language of rights’. She offers colourful accounts of Thomas Hobbes’s attempts to reduce moral questions to a calculus of ‘felicity’ and ‘misery’, and of Jeremy Bentham’s fateful decision to replace them with the words ‘pleasure’ and ‘pain’. Anyone who speaks English will realise that pleasure is not really the opposite of pain (for one thing, it cannot usually be quantified, or located in a particular part of the body) and happiness is something else again; but Bentham and the utilitarians were on a mission to free humanity from moralistic superstition and did not want to be detained by verbal niceties. Instead they got on with legislation – notably the Anatomy Act of 1832, which guaranteed a steady supply of pauper corpses for medical research. No less importantly, they created, through the work of Alexander Bain and Herbert Spencer, a system of scientific psychology based on a supposed ‘law of pain and pleasure’, thus giving utilitarian values an ‘imprimatur of value-free science’, which was still intact in the submissions made by Heath and Skinner to the Kennedy commission in 1973 and is present in the latest utterances of neuroscientists and neuroeconomists.

Cathy Gere is generally a self-effacing author, but she does give us a tantalising glimpse of herself as a student in Oxford in the 1980s. One day she read a book by R M Hare, the university’s resident utilitarian, and experienced a shattering conversion: she dropped out and became a full-time political activist, convinced that ‘the present must be sacrificed to the future, the few to the many, and the rich to the poor’. She has now repented of her ‘idiotic vanguardism’, but in terms of unintended consequences the adventure turned out well, giving her first-hand experience of the power of philosophical ideas and transforming her into a wonderfully imaginative and insightful historian.