42 PROLOGUE I 



For me/ the doctrine of evolution is no specula- 

 tion, but a generalisation of certain facts, which 

 may be observed by any one who will take the 

 necessary trouble. These facts are those which 

 are classed by biologists under the heads of 

 Embryology and of Palaeontology. Embryology 

 proves that every higher form of individual life 

 becomes what it is by a process of gradual differ- 

 entiation from an extremely low form ; palseonto - 

 logy proves, in some cases, and renders probable in 

 all, that the oldest types of a group are the 

 lowest; and that they have been followed by a 

 gradual succession of more and more differentiated 

 forms. It is simply a fact, that evolution of the 

 individual animal and plant is taking place, as a 

 natural process, in millions and millions of cases 

 every day ; it is a fact, that the species which have 

 succeeded one another in the past, do, in many 

 cases, present just those morphological relations, 

 which they must possess, if they had proceeded, 

 one from the other, by an analogous process of 

 evolution. 



The alternative presented, therefore, is : either 

 the forms of one and the same type say, e.g., that 

 of the Horse tribe l arose successively, but inde- 

 pendently of one another, at intervals, during 

 myriads of years ; or, the later forms are modified 



1 The general reader will find an admirably clear and concise 

 statement of the evidence in this case, in Professor Flower's 

 recently published work The Horse: a Study in Natural History, 



