Similar results were obtained by the study of human inventions. It has been noted before that apes and monkeys sometimes use stones for defence, and in a way the artificial shelters of animals indicate the beginnings of invention. In this sense we may seek for the origin of implements and utensils among animals. In the earliest times when human remains appear on the surface of the earth, we find man using simple stone implements which are formed by rough chipping, but the multiplicity of forms of implements increases gradually. Since many implements may have been made of perishable materials, we are not able to tell whether at a very early time the implements and utensils used were really confined to the few stone objects that may now be recovered; but certainly the implements were few, and, comparatively speaking, simple. From this time on, the uses of fire, and of tools for cutting and striking, for scraping and perforating, have increased in number and complexity, and a gradual development may be traced from the simple tools of primitive man to the complex machinery of our times. The inventive genius of all races and of unnumbered individuals has contributed to the state of industrial perfection in which we find ourselves. On the whole, inventions once made have been kept with great tenacity, and, owing to incessant additions, the available resources of mankind have constantly been increased and multiplied. An excellent example of the general theory of evolution of civilization is found in the theory of evolution of agriculture and of the domestication of animals as outlined by Otis T. Mason, W J McGee, and Hahn. They point out how, in the earliest beginnings of social life, animals, plants, and man lived together in a definite surrounding, and how, owing to the conditions of life, certain plants multiplied to the exclusion of others, and how certain animals were suffered in the neighborhood of the human camp. Through this condition of mutual sufferance and promotion of mutual interests, if I may use this term, a closer association between plants, animals, and man developed, which ultimately led to the beginnings of agriculture and to the actual domestication of animals.