Though all these desert-born characteristics and customs have a certain interest for the sociologist, they possess only minor importance in comparison with the religious spirit of pastoral nomads, which is always fraught with far-reaching historical results.  The evidence of history shows us that there is such a thing as a desert-born genius for religion.  Huc and Gabin testify to the deeper religious feeling of the Buddhist nomads of the Central Asia plateaus, as compared with the lowland Chinese.  The three great monotheistic religions of the world are closely connected in their origin and development with the deserts of Syria and Arabia.  The area of Mohammedism embraces the steppe zone of the Old World[1181] from Senegambia and Zanzibar in Africa to the Indus, Tarim and the upper Obi, together with some well watered lands on its margins.  It comprises in this territory a variety of races—­Negroes, Hamites, Semites, Iranians, Indo-Aryans, and a long list of Mongoloid tribes.  Here is a psychological effect of environment.  The dry, pure air stimulates the faculties of the desert-dweller, but the featureless, monotonous surroundings furnish them with little to work upon.  The mind, finding scant material for sustained logical deduction, falls back upon contemplation.  Intellectual activity is therefore restricted, narrow, unproductive; while the imagination is unfettered but also unfed.  First and last, these shepherd folk receive from the immense monotony of their environment the impression of unity.[1182] Therefore all of them, upon outgrowing their primitive fetish and nature worship, gravitate inevitably into monotheism.  Their religion is in accord with their whole mental make-up; it is a growth, a natural efflorescence.  Therefore it is strong.  Its tenets form the warp of all their intellectual fabrics, permeate their meager science and philosophy, animate their more glorious poetry.  It has moreover the fanaticism and intolerance characterizing men of few ideas and restricted outlook upon life.  Therewith is bound up a spirit of propaganda.  The victories of the Jews in Palestine, Syria and Philistia were the victories of Jehovah; the conquests of Saladin were the conquests of Allah; and the domain of the Caliphate was the dominion of Islam.

[Illustration:  DISTRIBUTION OF RELIGIONS IN THE OLD WORLD (World map showing distribution of Christians, Mohammedans, Brahmans, Buddhists, and Heathen).]

[Sidenote:  Fanaticism as a force in nomad expansion.]

The desert everywhere, sooner or later, drives out its brood, ejects its people and their ideas, like those exploding seed-pods which at a touch cast their seed abroad.  The religious fanaticism of the shepherd tribes gives that touch; herein lies its historical importance.  Mohammedism, fierce and militant, conduced to those upheavals of migration and conquest which since the seventh century have so often transformed the political geography of the Old World.  The