They say that the secret of comedy is timing, but time kills most jokes. The eclipse of the sensibility that hatched a joke is sure to prevent the splitting of sides. Chaplin’s tragicomedy was more sophisticated than Keaton’s slapstick, but Keaton is funnier to us. Chaplin’s mawkish plays for sympathy seem sentimental, his mock-childish pouting manipulative. But gurning, humiliation, pratfalls, sex jokes and rudeness are a joy forever. So Groucho Marx, born in 1890, a few months after Chaplin and five years before Keaton, will be poking Margaret Dumont with his cigar for a while yet.

The other way to kill a joke is to explain it. In Groucho Marx: The Comedy of Existence, the American critic Lee Siegel attempts double jocular homicide by unpicking Groucho’s humour in its historical context. This book is part of Yale University Press’s excellent Jewish Lives series but, though Siegel draws many links between the life and the work, his book is not so much a biography as a search for the psychological wellsprings of Groucho’s theatre of cruelty.

Siegel finds his ‘Rosebud’ in the oedipal drama of the Marx family flat in Yorkville, Manhattan. Groucho began life as Julius, the third of five sons who slept ‘like sardines’ in a single bed. He described his father, Frenchie, as a philanderer, an ineffectual gambler and ‘the most inept tailor