Trying to reconcile a belief in the literal truth of the Bible with the facts of the world as we observe it has never been the easiest of things. But heaven knows, people did try. Well enough known, I suppose, is the work of the 17th-century Archbishop of Armagh, James Ussher, who totted up all those begats to establish that the creation of the earth took place at six in the afternoon on 23 October 4005 bc.