When, in the slow procession of the ages, man was developed on this planet, the change worked by his appearance was at first slight. Further ages passed while he groped and struggled by infinitesimal degrees upward through the lower grades of savagery; for the general law is that life which is advanced and complex, whatever its nature, changes more quickly than simpler and less advanced forms. The life of savages changes and advances with extreme slowness, and groups of savages influence one another but little. The first rudimentary beginnings of that complex life of communities which we call civilization marked a period when man had already long been by far the most important creature on the planet. The history of the living world had become, in fact, the history of man, and therefore something totally different in kind as well as in degree from what it had been before.