What is called for is a clear knowledge of the course of evolution of this earliest institution and an understanding of the reasons for its changes, that we may discriminate to-day between that which is vital and permanent in home life and that which is unessential and injurious. We may follow without difficulty the evolution of each and all the essential constituents of home, mark the introduction of non-essentials, show the evils resultant from forced retention of earlier forms; in a word, we may study the evolution of the home precisely as we study that of any other form of life. Take that primal requisite of safety and shelter which seems to underlie all others, a place where the occupant may be protected from the weather and its enemies. This motive of home-making governs the nest-builder, the burrow-digger, the selector of caves; it dominates the insect, the animal, the savage, and the modern architect. Dangers change, and the home must change to suit the danger. So after the caves were found insufficient, the lake-dwellers built above the water, safe when the bridge was in. The drawbridge as an element of safety lingered long, even when an artificial moat must needs be made for lack of lake. When the principal danger is cold, as in Arctic regions, the home is built thick and small; when it is heat, we build thick and large; when it is dampness, we choose high ground, elevate the home, lay drains; when it is wind, we seek a sheltered slope, or if there is no slope, plant trees as a wind-break to protect the home, or, in the worst cases, make a "cyclone cellar." The gradual development of our careful plastering and glazing, our methods of heating, of carpeting and curtaining, comes along this line of security and shelter, modified always by humanity's great enemy, conservatism. In these mechanical details, as in deeper issues, free adaptation to changed conditions is hindered by our invariable effort to maintain older habits. Older habits are most dear to the aged, and as the aged have always most controlled the home, that institution is peculiarly slow to respond to the kindling influence of changed condition. The Chaldeans built of brick for years unnumbered, because clay was their only building material. When they spread into Assyria, where stone was plenty, they continued calmly putting up great palaces of sunbaked brick,--mere _adobe_,--and each new king left the cracking terraces of his predecessor's pride and built another equally ephemeral. The influence of our ancestors has dominated the home more than it has any other human institution, and the influence of our ancestors is necessarily retroactive.