The mode of life of all the Eskimo, as F. Boas[806] has pointed out, is fairly uniform and depends on the distribution of food at the different seasons. The migrations of game compel the natives to move their habitations from time to time, and as the inhospitable country does not produce vegetation to an extent sufficient to support human life they are forced to depend entirely upon animal food. The abundance of seals in Arctic America enables man to withstand the inclemency of the climate and the sterility of the soil. The skins of seals furnish the materials for summer garments and for the tent, their flesh is almost their only food, and their blubber their indispensable fuel during the long dark winter when they live in solid snow houses. When the ice breaks up in the spring the Eskimo establish their settlements at the head of the fiords where salmon are easily caught. When the snow on the land has melted in July the natives take hunting trips inland in order to obtain the precious skins of the reindeer, or of the musk-ox, of whose heavy pelts the winter garments are made. Walrus and the ground seal also arrive and birds are found in abundance and eaten raw. The Eskimo[807] occupy more than 5000 miles of seaboard from north-east Greenland to the mouth of the Copper river in western Alaska. Many views have been advanced as to the position of their centre of dispersion; most probably it lay to the west of Hudson Bay. Rink[808] is of opinion that they originated as a distinct people in Alaska, where they developed an Arctic culture; but Boas[809] regards them "as, comparatively speaking, new arrivals in Alaska, which they reached from the east." A westward movement is supported by myths and customs, and by the affinities of the Eskimo with northern Asiatics. There was always hostility between the Eskimo and the North American Indians, which, apart from their very specialised mode of life, precluded any Eskimo extension southwards. The expansion of the Eskimo to Greenland is explained by Steensby[810] as follows:--the main southern movement would have followed the west coast from Melville Bay, rounded the southern point and proceeded some distance up the east coast. From the Barren Grounds north-west of Hudson Bay the Polar Eskimo followed the musk-ox, advanced due north to Ellesmere Land, then crossed to Greenland, and, still hunting the musk-ox, advanced along the north coast and down the east coast towards Scoresby Sound. Another line of migration apparently started from the vicinity of Southampton Island and pursued the reindeer northwards into Baffin Land; on reaching Ponds Inlet these reindeer-hunting Eskimo for the most part turned along the east coast.