The Importance of Surnames

When did when did surnames become locked on permanent? What I mean by that is imagine back in medieval times, we're known as John the Miller. If you have a son who became say a barrel maker, you might be John the Cooper. But it's some stage that becomes locked and all this progeny will remain Cooper's up till the present day. The same thing could be said of your own name, O'Brien. When are why did we stop using those trade names and son of? And it got locked in and probably why? There must have been a reason. Simon, is it Sheffield? Hi, I've got an answer. Why do plastic footballs wobble