So it is with any comparison of animal work with the work of man, in whatever field. The crudest human endeavor is superior to the best non-human efforts; and the explanation is found always in the fact that the ingenuity of man has enabled him to find artificial aids that add to his power of manipulation. So large a share have these artificial aids taken in man's evolution, that it has long been customary, in studying the development of civilization, to make the use of various types of implements a test of varying stages of human progress. SCIENCE AND CIVILIZATION The student of primitive life assures us, basing his statements on the archæological records, that there was a time when the most advanced of mankind had no tools made of better material than chipped stone. By common consent that time is spoken of as the Rough Stone Age. We are told that then in the course of immeasurable centuries man learned to polish his stone implements, doubtless by rubbing them against another stone, or perhaps with the aid of sand, thus producing a new type of implement which has given its name to the Age of Smooth or Polished Stone. Then after other long centuries came a time when man had learned to smelt the softer metals, and the new civilization which now supplanted the old, and, thanks to the new implements, advanced upon it immeasurably, is called the Age of Bronze. At last man learned to accomplish the wonderful feat of smelting the intractable metal, iron, and in so doing produced implements harder, sharper, and cheaper than his implements of bronze; and when this crowning feat had been accomplished, the Age of Iron was ushered in. By common consent, students of the history of the evolution of society accept these successive ages, each designated by the type of implements with which the world's work was accomplished, as representing real and definite stages of human progress, and as needing no better definition than that supplied by the different types of implements. Could the archæologist trace the stream of human progress still farther back toward its source, he would find doubtless that there were several great epochal inventions preceding the time of the Rough Stone Age, each of which was in its way as definitive and as revolutionary in its effects upon society, as these later inventions which we have just named. To attempt to define them clearly is to enter the field of uncertainty, but two or three conjectures may be hazarded that cannot be very wide of the truth.