An enervating climate did its work in slaking their energies; but more radical still was the change wrought by the contrast of poverty and abundance, enforced asceticism and luxury, presented by the old and new home.

The restless, tireless shepherds became a sedentary, agricultural people; the abstemious nomads,--spare, sinewy, strangers to indulgence--became a race of rulers, revelling in luxury, lording it over countless subjects; finally, their numbers increased rapidly, no longer kept down by the scant subsistence of arid grasslands and scattered oases.
In a similar way, the Arab of the desert became transformed into the sedentary lord of Spain.

In the luxuriance of field and orchard which his skilful methods of irrigation and tillage produced, in the growing predominance of the intellectual over the nomadic military life, of the complex affairs of city and mart over the simple tasks of herdsman or cultivator, he lost the benefit of the early harsh training and therewith his hold upon his Iberian empire.

Biblical history gives us the picture of the Sheik Abraham, accompanied by his nephew Lot, moving up from the rainless plains of Mesopotamia with his flocks and herds into the better watered Palestine.

There his descendants in the garden land of Canaan became an agricultural people; and the problem of Moses and the Judges was to prevent their assimilation in religion and custom to the settled Semitic tribes about them, and to make them preserve the ideals born in the starry solitudes of the desert.
[Sidenote: Retrogression in new habitat.] The change from the nomadic to the sedentary life represents an economic advance.