Such dull intervals seem to have been necessary for developing, formulating, classifying, and testing the innumerable details and inferences that the discoveries of the active periods produced. While mankind in general has contributed to the total of our intellectual treasures, some races have been more active in this way than others. For this reason it is advisable to briefly survey the more recent discoveries about the ancestors of existing peoples. Indo-Malaysia, parts of central Asia, and the valleys of the Tigris and Euphrates rivers in Mesopotamia are variously credited with having been the cradle of the human race. It should be understood, however, that we are only permitted to speak authoritatively of existing races, because the land forms of the earth have undergone such remarkable changes that we can know little definitely about the earlier periods of human history. For the purposes of the history of science, while bearing in mind these qualifying suggestions, we may accept the statement that man's ancestors originated in proximity to India. It was around the waters of the Persian Gulf that the earliest known civilizations arose. The people who founded them came from central Asia. They had reached a considerable degree of culture, which suggests that they themselves came from earlier centers of civilization. The study of prehistoric antiquity is termed archæology. Its principal periods have been divided, for convenience, into the Stone, Bronze, and Iron Ages. Each of these is distinguished by the substances used for tools. In the Stone Age men used stone spearheads, arrows, and knives, whereas in the Iron Age similar things were made of iron or copper. The science of mankind is known as Anthropology. It deals with the innumerable steps in the evolution of mankind from remote periods, and with the primitive development of the arts, sciences, and religion. Yet it is one of the youngest of the sciences. One of its essential teachings is that heredity and racial predispositions play, and always have played, more important parts in man's evolution, and in the development of civilization, than environment and education. Hereditary tendencies, such as the religious, moral, and æsthetic instincts have been indispensable in preserving and developing all the races of mankind. Moral discipline has been the chief factor in self-control, and therefore in civilization. It is because the moral sense has proved so beneficial to the human race, and is the most powerful of our instinctive desires, that mankind always has been and must be religious. It controls man's knowledge, desires, and will, and has dominated the race since our early ancestors began to think.