Masterpieces of Science 



knowledge extends, the history of the horse-type 

 is exactly and precisely that which could have 

 been predicted from a knowledge of the principles 

 of evolution. And the knowledge we now pos- 

 sess justifies us completely in the anticipation, 

 that when the still lower Eocene deposits, and 

 those which belong to the Cretaceous epoch, have 

 yielded up their remains of ancestral equine 

 animals, we shall find, first, a form with four com- 

 plete toes and a rudiment of the innermost or 

 first digit in front, with probably, a rudiment of 

 the fifth digit in the hind foot;* while, in still 

 older forms, the series of the digits will be more 

 and more complete, until we come to the five- 

 toed animals, in which, if the doctrine of evolu- 

 tion is well founded, the whole series must have 

 taken its origin. 



That is what I mean by demonstrative evi- 

 dence of evolution. An inductive hypothesis is 

 said to be demonstrated when the facts are shown 

 to be in entire accordance with it. If that is not 

 scientific proof, there are no merely inductive 

 conclusions which can be said to be proved. And 

 the doctrine of evolution, at the present time, 

 rests upon exactly as secure a foundation as the 

 Copernican theory of the motions of the heavenly 

 bodies did at the time of its promulgation. Its 

 logical basis is precisely of the same character — 



* Since this lecture was delivered, Professor Marsh has 

 discovered a new genus of equine mammals (Eohippus) 

 from the lowest Eocene deposits of the West, which corre- 

 sponds very nearly to this description. — American Journal 

 of Science, November, 1876. 



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