The dysfunctional families of the famous are a source of endless fascination. Our desire to know about the odd and inadequate individuals who share genes with the elite, from John Major’s garden-gnome-enthusiast brother to the Markles, seems to be a way of reminding ourselves that its members are human after all.

The theme of the disappointing sibling is not a new one. While Jane Austen didn’t perhaps achieve the full recognition that she deserved in her lifetime, even then she outshone her brothers. Henry, the fourth son of the Austen family, took holy orders, but only after his attempts to succeed in banking and the militia had failed. His interview with the bishop, for which he had laboriously reacquainted himself with koine Greek, consisted of the prelate placing his hand on the New Testament and saying, ‘As for this book, Mr Austen, I dare say it is some years since either you or I looked into it.’ Charles Austen, the family’s youngest son, enjoyed a moderately impressive career in the navy.

In fairness to the male Austens minor, the position of younger sons in 18th- and early 19th-century England was an uncertain one. A father of means would invariably leave almost everything to his eldest son, minus allowances and dowries set aside to enable his daughters to live comfortably or marry well. Younger sons more often than not were left with practically nothing except an expectation that they would continue to live, socialise and generally carry themselves in a manner that befitted the rank to which they had been born. As such, non-manual professions, ancient vocations such as the Church and the law, and military or naval service became more or less the only ways in which a gentleman could ‘work for his living without ceasing to be a gentleman’.

It wasn’t only men from the relatively middling classes, such as the younger Austen brothers, who found themselves in this delicate situation. Alexander Gordon, a younger brother of the Earl of Aberdeen, prime minister from 1852 to 1855, was sent into the army. He served in the Peninsular War but spent much of his time in Spain being chastised via letter for failing to navigate the system of import duty when securing pieces of art for his eldest brother back home. Such fraternal oversight abruptly ended when Alexander was butchered at Waterloo.

Some, of course, made a success of their careers, even if they weren’t their first choices. The cleric and wit Sydney Smith was a younger son who had to enter the Church when his elder brother decided that he rather fancied a go at Sydney’s first choice of the law – two Smiths in one place was considered a little de trop. Of course, Sydney’s fate in holy orders is well known: he became a canon of St Paul’s (only missing out on a bishopric due to his well-publicised liberalism) and earned a reputation as ‘the wittiest of wits and the Smithiest of Smiths’. One can’t help wondering whether his elder brother regretted his rush to don the barrister’s wig. Even the great titans of the age had to start somewhere: the Duke of Wellington was considered inferior in talent to his elder brother, Lord Mornington, and only carried on with a military career when his attempts to secure a middling position in the Irish civil service were knocked back. How different the Battle of Waterloo might have been if Arthur Wellesley had succeeded in his desire to become the man who appointed the captain of the Dublin to Holyhead ferry.

Whether successes or failures, they are all here in Rory Muir’s meticulously researched and eminently readable Gentlemen of Uncertain Fortune. Beginning with an intriguing Austen-related counterfactual – what would the Bennet sisters from Pride and Prejudice have got up to had they been boys? – he draws a brilliant portrait of Regency Britain through the careers of its younger sons. As well as the Church, the law, the army and the navy, the worlds of medicine, commerce and politics and even the panoply of positions available on the Indian subcontinent are explored through examples of the young men who managed (or catastrophically failed) to make the careers into which they had been shunted work for them. In the process, Muir succeeds in presenting a panorama of a society as much as the stories of those individuals themselves.

And what of the Bennets, or, for that matter, the Austens (for the story of Jane’s siblings is told in full too)? Well, far be it from me to spoil the surprise of Muir’s conclusion, but suffice to say that the portrait of a male Lydia sloping around a seaside town on half pay is particularly finely painted, perfectly intertwining pathos and bathos. Indeed, that might be said about the book as a whole: underneath a compellingly narrated analysis of society in Regency England lie any number of stories, all equally well told, that are occasionally glorious, often ridiculous and at times deeply sad. Historians rarely succeed in balancing the macro and micro narratives that make up the delicate fabric of the past. To do so, as Rory Muir has done here with such élan, is no mean feat.