[Sidenote:  Land in relation to agriculture.]

With transition to the sedentary life of agriculture, society makes a further gain over nomadism in the closer integration of its social units, due to permanent residence in larger and more complex groups; in the continuous release of labor from the task of mere food-getting for higher activities, resulting especially in the rapid evolution of the home; and finally in the more elaborate organization in the use of the land, leading to economic differentiation of different localities and to a rapid increase in the population supported by a given area, so that the land becomes the dominant cohesive force in society. [See maps pages 8 and 9.]

[Sidenote:  Migratory agriculture]

Agriculture is adopted at first on a small scale as an adjunct to the chase or herding.  It tends therefore to partake of the same extensive and nomadic character[112] as these other methods of gaining subsistence, and only gradually becomes sedentary and intensive.  Such was the superficial, migratory tillage of most American Indians, shifting with the village in the wake of the retreating game or in search of fresh unexhausted soil.  Such is the agriculture of the primitive Korkus in the Mahadeo Hills in Central India.  They clear a forested slope by burning; rake over the ashes in which they sow their grain, and reap a fairly good crop in the fertilized soil.  The second year the clearing yields a reduced product and the third year is abandoned.  When the hamlet of five or six families has exhausted all the land about it, it moves to a new spot to repeat the process.[113]

The same superficial, extensive tillage, with abandonment of fields every few years, prevails in the Tartar districts of the Russian steppes, as it did among the cattle-raising Germans at the beginning of their history.  Tacitus says of them, Arva per annos mutant et superest ager,[114] commenting at the same time upon their abundance of land and their reluctance to till.  Where nomadism is made imperative by aridity, the agriculture which accompanies it tends to become fixed, owing to the few localities blessed with an irrigating stream to moisten the soil.  These spots, generally selected for the winter residence, have their soil enriched, moreover, by the long stay of the herd and thus avoid exhaustion.[115] Often, however, in enclosed basins the salinity of the irrigating streams in their lower course ruins the fields after one or two crops, and necessitates a constant shifting of the cultivated patches; hence agriculture remains subsidiary to the yield of the pastures.  This condition and effect is conspicuous along the termini of the streams draining the northern slope of the Kuen Lun into the Tarim basin.[116]

[Sidenote:  Geographic checks to progress.]