512 THE CHANGING WORLD 



The final episode in equine history occurred in very recent times, 

 even as late as after Adam's ancestors had become human beings 

 and had passed through a series of many civilizations that arose and 

 fell. Then, preceding the comparatively recent Christian era, there 

 came long dark ages until yesterday, in the seventeenth century, 

 adventurous Spaniards brought to South America domesticated 

 descendants of the European branch of this long, royal equine line. 

 Some of these much traveled horses, being set free, "went native," 

 and became the wild mustangs and broncos which spread from 

 South America, and finally came to reoccupy their ancestral plains 

 in North America. Thousands of skeletons of fossil horses all along 

 the evolutionary line have been discovered, and may be seen in vari- 

 ous museums. Their sequence is so plain that even the uninitiated 

 can understand it and be convinced of the truth. When once this 

 documentary evidence is realized, the fact of evolution is established 

 beyond any doubt. 



A common difficulty in accepting the evidences of organic evolu- 

 tion is inability to appreciate the length of time that it has taken. 

 It never could have come about within a few thousand years. How 

 ridiculous it is to expect anything like a laboratory demonstration 

 of an accomplishment which has taken millions of years to effect ! 

 The geologist, however, presents us with all the years we could 

 possibly need to enable us to allow for the slow processes of evolu- 

 tion ; so many, in fact, that we grow intellectually footsore and 

 weary traveling backward in time. The story of the horse, for 

 example, occupied only a part of the Cenozoic era, or about one 

 tenth of the time since the dawn of the Paleozoic era in which the 

 general record of fossils begins. The fact that at this early time all 

 the large groups of animals except vertebrates were represented in 

 great diversity makes it reasonable to suppose that evolution of 

 organic forms did not start then, but had already been going on 

 long enough to lead up to the Paleozoic differentiation of types. It 

 should be remembered that only in sedimentary rocks, the earliest 

 of which belong to the Paleozoic era, are fossil epitaphs recorded. 

 Many lines die out. Even the horse is on its last legs in an evolu- 

 tionary sense, with only a paltry half dozen or so living species left 

 out of all the past. 



Some of the inescapable conclusions of the occurrence of evolution 

 that are reached by an examination of the evidence from fossils are : 

 (a) that there is a general increase in complexity of organisms as time 



