Evolution thus makes the world over for us.  It shows us in what a complex web of vital and far-reaching relations we stand.  It gives us an outlook upon the past that is startling, and in some ways forbidding, yet one that ought to be stimulating and inspiring.  If we look back with a shudder we should look forward with a thrill.  If the past is terrible, the future is in the same degree cheering and inviting.  If we came out of those lowly and groveling forms, to what heights of being may we not be carried by the impetus that brought us thus far?  In fact, to what heights has it already carried us!

II

That the hazards of the past, to many forms of life, at least, have been real and no myth, is evident from the vast number of forms that have been cut off and become extinct; various causes, now hard to decipher, have worked together to the end, such as changed geographical conditions, changes of climate, affecting the food-supply, extreme specialization, like that of the sabre-toothed tiger whose petrified remains have been found in various parts of this continent, and who apparently was finally handicapped by his huge dental sabre.  Probably many more species of animals have become extinct than have survived, but none of these could have been in the line of man’s descent, else the human race would not have been here.  If the Eocene progenitor of the horse, the little four-toed eohippus, had been cut off, would not the world have been horseless to-day?  The horse in America became extinct, from some cause only conjectural, many tens of thousands of years ago.  Had the same fate befallen the horse in Europe and Asia, it seems probable that our civilization would have been far less advanced to-day than it is.

The fate of every species of mammal in our time seems to have been in the keeping of a single form in early Tertiary times.  The end of the Cretaceous or chalk period saw the extinction of the giant reptiles both of sea and of land, at the same time that it saw the appearance of a great many species of small and inconspicuous mammals, among which doubtless were our own humble forebears.  Extreme specialization in any direction may narrow an animal’s chances of survival; they have but one chance in the game of life, whereas an animal with a more generalized organization has many chances.  Man is one of the most generalized of animals; no special tools, no special weapons—­his hand many tools and weapons in one.  Hence he is the most adaptable of animals; all climes, all foods, all places are his; he is master of the land, of the sea, of the air.