4o6 ELEMENTS OF BIOLOGY 



o£ which, the Neanderthal, has characters which classify it as a 

 distinct human species, Homo neanderthaler. It is not regarded as 

 the ancestor of modern Man, Homo sapiens, but as a parallel branch 

 of the group, which has become extinct. Certainly it is clear that 

 at this time there were many primate forms, some distinctly apes 

 and others resembling Man, descended from some ancestral forms 

 as parallel derivatives. So modern Man is in no way the descendant 

 of apes or monkeys; rather Man, apes, and monkeys are distantly 

 related modern representatives of a common ancient primate an- 

 cestor which appeared early in the Tertiary Era. 



The two examples given illustrate a general principle that has 

 been obscure to the uninformed, namely, that in giving rise to 

 modern forms of animals and plants, ancient types have disappeared 

 in the process, as a parent paramcecium disappears when it divides 

 into two daughter animals. In other words, evolution has occurred 

 by a modification of the stock, not by throwing off of different types 

 with a preservation of the original in its primitive form. 



Evolution of the Horse. It has been possible to trace with 

 considerable accuracy the changes which have taken place in many 

 forms. One of the clearest cases is the history of the modern horse 

 (Fig. 225). In the early Tertiary Era are found the remains of a 

 small animal with distinctly horse-like characters but with five digits 

 on the fore feet and four on the hind feet. The middle digits in 

 both fore and hind feet are distinctly larger than the others and 

 the outer digits on the fore, and the inner digits on the hind feet 

 are reduced to rudiments. The rocks of succeeding geological peri- 

 ods contain skeletons of larger animals of this type, with the middle 

 digits still more emphasized and the other digits still more reduced. 

 These differences in the feet are accompanied by similar transitional 

 changes in other skeletal characters. It has thus been possible to 

 trace the origin of the modern horse almost step by step to this 

 early Eocene animal, Eohippus. 



In summary, three principles are the essential derivatives of the 



