MAN FROM THE FARTHEST PAST 
reptiles of air, land, and sea, and the rise of birds; through 
the Eocene, Oligocene, Miocene, and Pliocene, which saw the 
dawn of the age of mammals, and their development to 
cover and rule the earth; till finally, after the lapse of hun- 
dreds of millions of years, man came upon the scene. 
Within the comparatively brief epoch of a few hundred 
thousand years at most, he has become master of the world. 
Other creatures hold their lives at his pleasure; the earth 
yields her stores of fruits, fuel, and minerals to his machin- 
ery; he collects power from the rivers and the sun; he com- 
municates his thoughts around the world almost instan- 
taneously; he explores the universe with his telescope and 
spectroscope; and he rides on air, land, and water at 
speeds exceeding that of the swiftest of the birds. 
There are at present in the world approximately 600,000 
known species of insects, several hundred thousand other 
invertebrates and nonmammalian vertebrates, and 15,000 
mammals. Until comparatively recent times, these were 
nonexisting, and other species, now extinct, prevailed. 
Their numbers can not now be estimated, because of the 
imperfect record which paleontology has thus far disclosed. 
Nor is the present number complete. Every year adds 
thousands of newly discovered species to the already 
hugely swollen list of creatures of the present and the past. 
It has even been estimated that the unknown insect 
species are really ten times as numerous as those hitherto 
described. 
The immense numbers of species and the changes there- 
in from epoch to epoch which have marked the past history 
of the earth, and the tremendous time scale indicated by 
the study of the slow alterations and great thickness of 
stratified rocks no less than by the discovery of the trans- 
mutation of radium, combine both to accentuate and to 
answer the question: What is the origin of species? With- 
out other evidences than those just mentioned, the mind 
would tend to conclude that the species have been formed 
by gradual divergences of forms exposed to different en- 
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