WHETHER the individual or the generation be pessimistic or optimistic in historical perspective, it is undeniable (as I have said before) that there have been certain cataclysmic events from time to time which have compelled a revision of values -a general modification of outlook. It is a misfortune that we cannot trace things back to the beginnings of conscious thought, because we require some written record to help us. No doubt there must have been such revisions of outlook when man first discovered the use of fire, or of agriculture, or of the domestication of animals. We can have a better appreciation of what happened when the people who had discovered the use of metal weapons burst in upon their neolithic predecessors. But we can only guess at the unpleasant surprise to the vanquished.