It was the Second World War ditty that mocked not just Hitler but the whole Nazi high command for their lack of sexual prowess. Sung to the tune of the Colonel Bogey March, it went: ‘Hitler has only got one ball, ‘Göring has two but very small, ‘Himmler is rather sim’lar, ‘But poor old Goebbels has no balls at all.’ Now, a two-part Channel 4 documentary Hitler’s DNA: Blueprint Of A Dictator has discovered that the song was not simply a piece of Allied propaganda but rooted in reality – at least so far as the dictator was concerned. After...