A strange thing about humans is their capacity for blind rage. Rage is presumably an emotion resulting from survival instinct, but the surprising thing about it is that we do not deploy(对付)it against other animals. If we encounter a dangerous wild animal -- a poisonous snake or a wild cat -- we do not fly into a temper. If we are unarmed, we show fear and attempt to back away if we are suitably armed, we attack, but in a rational manner not in a rage. We re serve rage for our own species. It is hard to see any survival value in attacking ones own, but if we take account of the long competition which must have existed between our own subspecies and others like Neanderthal man(尼特尔人)-- indeed others still more remote from us than Neanderthal man -- human rage becomes more comprehensible. In our everyday language and behavior. there are many reminders' of those early struggles. We are always using the words 'US and them'.. 'Our' side is perpetually trying to do down the 'other' side. In games we artificially create other subspecies we can attack. The opposition of 'us' and 'them' is the touchstone of the two party system of 'democratic' politics. Although there are no very serious consequences to many of these modern psychological representations of the 'us and them' emotion, it is as well to remember that the original aim was not to beat the other subspecies in a game but to exterminate it. The readiness with which humans allow them selves to be regimented(严密编组)has permitted large armies to be formed, which, taken together with the 'us and them' blind rage, has led to destructive(毁灭性的)clashes within our subspecies itself. The First World War is an example in which Europe divided itself into two imaginary subspecies. And there is a similar extermination battle now in Northern Ireland. The idea that there is a religious basis for this clash is illusory, for not even the Pope has been able to control it. The clash is much more primitive than the Christian religion, much older in its emotional origin. The conflict in Ireland is unlikely to stop until a greater primitive fear. is imposed from outside the community, or until the combatants become exhausted. According to the author, the surprising aspect of human anger is ______.