Millions of years have passed since life appeared on the earth. Gradually higher forms have followed lower ones in the sea and on the land. But not all of the lower forms have gone. All grades of plants and animals still flourish, but the dominant class in each age is more highly organized than the class that ruled the preceding age.
To discover the earth's treasure, and to turn it to use; to tame wild animals and wild plants, and make them serve him; to create ever more beautiful and more useful forms in domestication; to find out the earth's life story, by reading the pages of the great stone book—these are undertakings that waited for man's coming.