When, later, the sail was functionally replaced by steam, man became virtually independent of the wind, and only the name of trade wind remains to carry us back to the period when the ocean breezes determined his movements and his commerce.
Turning now to the surface of the land, we may note that regions which are snow-covered in winter offer special facilities for rapid locomotion. In the northern part of North America, both in the tundra and the forest region, the aborigines used both snow-shoes and sledges. The Eskimos to the north use dogs to draw their heavy sledges, but to the south the Indians used a lighter form of sledge, which was dragged by women, and therefore represents a much more primitive form of transport. Even down to the present time the conditions in Arctic America are such that transport facilities are very much greater in winter than in summer, except in regions close to navigable rivers.
Snow-sledges and snow-shoes of course occur also on the European side of the Atlantic to the north, but the domesticated reindeer replaces the dog in Lapland as the means of traction, though dogs are used in other parts of the tundra region of the old world.
Apart from snow-covered regions deserts afford another example of areas in which the surface is frequently so uniform that friction is greatly reduced, and rapid movement is possible without specially prepared tracks. In the Sahara, for example, which is far from being the waste of sand which is popularly imagined, there are great areas of almost level surface, where “the soil is firm and elastic, strewn with gravel, and like a garden walk.” In Algiers it is possible to drive in high dog-carts over the plateau region in any direction, regardless of roads, and in parts of the North American desert the same thing is true. It has been suggested, indeed, that wheeled vehicles were invented by races living near desert regions, and that the invention thus preceded the making of roads.
In the general case, however, rapid movement is bound up with the existence of roads or tracks. In parts of North America, notably in the region south and east of the Great Lakes, where the rivers are generally unsuitable for navigation by very primitive forms of boats, the original Indian inhabitants mostly moved by means of “trails” through the woods. These trails were the lines of migration of the larger mammals, especially of the bison, and it is a remarkable fact that the roads made later by the white immigrants sometimes followed these old trails, which proved to be the most convenient routes. This suggests one method in which roads and paths might originate, but the Indian trails, like the African negroes’ paths through the forest, were excessively narrow and inconvenient.
Another stage in road evolution is well illustrated in many mountain regions, i. e. in the less-frequented parts of the Alps. Here the mountains are crossed by narrow tracks, which die away at intervals and then reappear. They are chiefly used by the herdsmen and cattle, during the periodical migrations to the higher pastures, and this fact gives rise to certain peculiarities. Where the region traversed is very steep the path is usually well marked, and there may be even attempts to improve difficult parts so as to render it more practicable. When the ground becomes more level the path dies away, or divides up into a multitude of minor tracks. The reason is obvious. In the steep regions the cows must keep together, and their constant journeyings render the road well marked. It must also be easy enough to permit of the passage of the animals, whose agility has its limits. Where the ground is level grass usually grows, and here the cattle spread out in all directions to feed, and the path naturally dies away. It may be marked on the map as going on to cross a col and so reach another valley, but as the number of persons making the traverse is likely to be small, the track is badly marked, as many a tourist has found to his cost.
From such tracks, which are little more than aids in crossing specially difficult areas, to the well-made roads which traverse the civilised countries of the world the gap is great, for, though the Romans made magnificent roads, after their time there was a rapid decay in the art, and the well-kept roads of the western countries of Europe are things but of yesterday.
With the development of tracks and roads, as distinct from a mere animal trail through the bush, there comes the possibility of using pack-animals and wheeled vehicles for transport. The two do not necessarily occur together. Thus in China and Japan wheeled vehicles are drawn by human beings, though in China the wheelbarrows drawn by human porters have also sails to aid their propulsion.
The use of animals, whether as pack-animals or for traction, means a relatively high degree of civilisation, and means also a food supply normally more than enough for the human members of the community. In many parts of tropical Africa, despite the tropical luxuriance of many of the food plants, and the absence of winter, there is practically no food reserve, and the normal condition is that the whole group is within measurable reach of starvation, should any one of a whole series of probable or possible accidents happen to the plantations. Under such conditions large domestic animals, requiring great quantities of food, cannot be kept.
Again, where the population is dense, and all the land is required to grow food for man, it is not possible to set aside regions for the pasturage of domestic animals, whose numbers must necessarily then be small. This is true of China and Japan, where domestic hoofed animals are few in number. The contrary condition is of course seen in new countries, like Australia and the Argentine, where there are far fewer men than sheep and cattle. The United States is beginning to pass from this condition, and there have been published already warnings to the community that it cannot go on giving up much of its fertile land to the growth of crops for its domestic animals, instead of for its citizens directly.