text: they got invented as the first names became more used and used.  The farmer 'john'from the farm became 'john farmer', the tax payer named 'john' who collected the tax became 'john taxman' and the boy called 'john' whos was born to 'john' became 'john mcjohn' 'john ap John' 'John O'John'.  There was also variants used such as in wales 'Evans' 'Ivan' means john and in other parts of europe 'john' is 'hans' and 'heinz'.