THE HAZARDS OF THE PAST 
as changed geographical conditions, changes of cli- 
mate, affecting the food-supply, extreme specializ- 
ation, 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 pro- 
genitor 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 ex- 
tinct, from some cause only conjectural, many tens 
of thousands of years ago. Had the same fate be- 
fallen the horse in Europe and Asia, it seems prob- 
able 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 rep- 
tiles 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 an- 
imal’s chances of survival; they have but one chance 
in the game of life, whereas an animal with a more 
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