Such acquisitions of external culture accompany man during the transition from his subsistence by the pure products of Nature to the cultivation of natural resources, cattle-breeding and agriculture--occupations necessitating the greatest unrest and mobility. The simple life in Nature incites men to wander forth that they may discover land adapted for their support; they rove about in search of roots as well as of living prey. The breeding of domestic animals also causes them to travel in the hope of finding ground for pasture; nor does agriculture in its primitive form tend to establish permanence of residence, although it contains within itself latent possibilities of developing a settled life, one of the most important factors in the progress of mankind. [Illustration: PRIMITIVE DWELLINGS OF TO-DAY: HOUSE-BOATS AT CANTON [Sidenote: Mankind “Settling Down”] Not only are there lake-dwellers to-day, as we have seen, but even large communities, as at Canton, in China, live in boats. ] Only fixed, domestic peoples are able to create great and lasting institutions, to store up the results of civilisation for distant later races, and to establish a developed, well-organised commercial and civil life. The transition from nomadism to life in permanent residences has, therefore, been one of the greatest steps in the development of humanity. At the time of the beginnings of agriculture, however, man was still a periodic wanderer. According to the field-grass system of cultivation, seed is sown in hastily-cleared ground, which soon becomes exhausted and is then abandoned. A migration follows and new land is cleared. This system continues until men learn to cultivate part of the land in a district, allowing the remainder to lie fallow for a time in order that the soil may recover; thus they remain fixed in their chosen district. Various circumstances--for example, the danger of enemies from without, and the difficulties attending migration--must have led to this change, the transition to the system of alternation of crops. The wanderings are confined to less extensive regions, the same fields are returned to after a few years, until finally the relation of patches under cultivation to fallow land is reduced to a system, and the time of wandering is past. [Illustration: THE BEGINNINGS OF COMMERCE: PRIMITIVE PEOPLE BARTERING IVORY TUSKS AND BULL-HIDES] [Sidenote: The coming of the Craftsman]