It is clear, for example, that if we go back in imagination to the very remotest ancestors of man that can be called human, we must suppose a vast and revolutionary stage of progress to have been ushered in by the first race of men that learned to make habitual use of the simplest implement, such as a mere club. When man had learned to wield a club and to throw a stone, and to use a stone held in the hand to break the shell of a nut, he had attained a stage of culture which augured great things for the future. Out of the idea of wielded club and hurled stone were to grow in time the ideas of hammer and axe and spear and arrow. Then there came a time--no one dare guess how many thousands of years later--when man learned to cover his body with the skin of an animal, and thus to become in a measure freed from the thraldom of the weather. He completed his enfranchisement by learning to avail himself of the heat provided by an artificial fire. Equipped with these two marvelous inventions he was able to extend the hitherto narrow bounds of his dwelling-place, passing northward to the regions which at an earlier stage of his development he dared not penetrate. Under stress of more exhilarating climatic conditions, he developed new ideals and learned to overcome new difficulties; developing both a material civilization and the advanced mentality that is its counterpart, as he doubtless never would have done had he remained subject to the more pampering conditions of the tropics. The most important, perhaps, of the new things which he was taught by the seemingly adverse conditions of an inhospitable climate, was to provide for the needs of a wandering life and of varying seasons by domesticating animals that could afford him an ever-present food supply. In so doing he ceased to be a mere fisher and hunter, and became a herdsman. One other step, and he had conceived the idea of providing for himself a supply of vegetable foods, to take the place of that which nature had provided so bountifully in his old home in the tropics. When this idea was put into execution man became an agriculturist, and had entered upon the high road to civilization.