WE have now reached a point at which we can bring our present argument to a head. We have ascertained that civilizations come to birth in environments that are unusually difficult and not unusually easy, and this has led us on to inquire whether or not this is an instance of some social law which may be expressed in the formula: 'the greater the challenge, the greater the stimulus'. We have made a survey of the responses evoked by five types of stimulus—hard countries, new ground, blows, pressures and penalizations—and in all five fields the result of our survey suggests the validity of the law. We have still, however, to determine whether its validity is absolute. If we increase the severity of the challenge ad infinitum, do we thereby ensure an infinite intensification of the stimulus and an infinite increase in the response when the challenge is successfully met ? Or do we reach a point beyond which increasing severity produces diminishing returns ? And, if we go beyond this point, do we reach a further point at which the challenge becomes so severe that the possibility of responding to it successfully disappears? In that case the law would be that 'the most stimulating challenge is to be found in a mean between a deficiency of severity and an excess of it'.
Is there such a thing as an excessive challenge? We have not yet encountered an example of such, and there are several extreme cases of the operation of challenge-and-response which we have not yet mentioned. We have not yet cited the case of Venice—a city, built on piles driven into the mud banks of a salt lagoon, which has surpassed in wealth and power and glory all the cities built on terra firma in the fertile plain of the Po; nor Holland—a country which has been actually salvaged from the sea, but yet has distinguished herself in history far above any other parcel of ground of equal area in the North European plain; nor Switzerland, saddled with her portentous load of mountains. It might seem that the three hardest pieces of ground in Western Europe have stimulated their inhabitants to attain, along different lines, the highest level of social achievement that has as yet been attained by any peoples of Western Christendom.
But there are other considerations. Extreme in degree though these three challenges are, they are limited'in range to only one of the two realms which constitute the environment of any society. They are challenges of difficult ground, no doubt, but on the