The origin of this relation is apparently traceable to one of the many forms of human association which have proved advantageous in the struggle for existence, when the value to a man and his wife of so protecting their offspring during childhood that there should be later on an array of lusty sons and industrious daughters thrust itself on their notice. The division of strenuous work, for instance, the pursuit and preparation of food, the effective defence of their rude shelters against the depredations of their foes, were substantial advantages to be derived in primitive times from the possession of a large group of children. Upon the youthful vigour and strength of their family the parents could rely also when overtaken by the weakness of old age or by accident or disease. These economic and sociological advantages were so early appreciated and are so widely adopted that traces of family life are to be detected in the history and customs of every tribe or community hitherto investigated. The bond thus formed, even amongst the lowest savages, first developed, then strengthened the ties of natural affection between a mother and her children and prolonged its emotional existence. In the case of the paternal parent, it is probable that the motives which incited him to make the efforts necessary for the protection of his helpless infants might more probably be found in the desire to leave an avenger on individual enemies and a feeling that funeral rites would be duly performed after his death, as well as his tribe strengthened in war. The gradual development of the human home has been admirably described by more than one writer, who has associated its evolution with the gregarious instinct, recognised in many of the higher forms of animal life.[104] Within reason, associated numbers represent power--power to preserve the progeny, therefore to maintain the numbers, which again in reason make for social support and independence. Power for defence, power to secure an adequate supply of food and ability to differentiate occupations, thus dividing labour, so that while the men of a family group were engaged in war or the chase, their womenkind devoted their attention to the creature comforts which promote health and efficiency--these are all factors which make for progress. VII. WOMAN'S VOCATION IN HOME AND FAMILY LIFE