In the cases above dealt with, however, and in many others, there is seen to have been _intellectual_ decay, in the sense of, first, a cessation of forward movement, and, next, a loss of the power to appreciate ideas once current. A common cause of such paralysis of the higher life is the malignant action of dogmatic religious systems, as in the cases of Persia, Jewry, Byzantium, Islam, Spain under Catholicism, and Scotland for two centuries under Protestantism. Such paralysis by religion may arise alike in a highly-organised but isolated State like Byzantium, and in a semi-civilised country like Anglo-Saxon England.[145] The special malignity of dogma in these cases is itself of course a matter for analysis and explanation. Other cases are partly to be explained by (_a_) the substitution of systematic militarism, always fatal to progressive culture, for a life of only occasional warfare, favourable to study among the leisured class.[146] But (_b_) there is reason to surmise a further and profoundly important cause of intellectual retrogression in the usage which develops the culture of a people for the most part in one sex only. The thesis may be ventured that whereas vigorous and creative brains may arise in abundance in a young civilisation, where the sexes are physiologically not far removed from the approximate equality of the semi-barbarous stage, the psychological divergence set up by mentally and physically training the males and not the females is likely to be unfavourable to the breeding of mentally energetic types. (12) Whether or not the last hypothesis be valid, it is clear that the co-efficient or constituent of intellectual progress in a people, given the necessary conditions of peace and sufficient food, is multiplication of ideas; and this primarily results from international contact, or the contact of wholly or partly independent communities of one people. Multiplication of arts and crafts is of course included under the head of ideas. But unless the stock of ideas is not merely in constant process of being added to among the studious or leisured class, but disseminated among the other classes, stagnation will take place among these, and will inevitably infect the educated class.