ANIMAL LIFE AND EVOLUTION 345 



shows such fundamental similarities as to indicate beyond 

 doubt an actual blood relationship of wider or closer degree 

 among them. The superficial differences among animals 

 evidently of common identity of basic structural plan are 

 exactly those which life under differing conditions would call 

 for as helpful modifications or adaptations. This same condi- 

 tion of fundamental likeness with superficial differences is true 

 also of the functions or physiology of animals. 



A close study of the complete life history or development of 

 an animal from beginning egg to full-grown adult condition, 

 reveals the fact that this course of personal development 

 shows striking similarities both with the paleontological record 

 and with the revelations of comparative anatomy. Ontogeny 

 is said to recapitulate phylogeny, by which is meant that each 

 animal in its personal development runs through swiftly, but 

 more or less obviously, a much abridged recapitulation of the 

 stages of the evolution of the species to which it belongs. 



Finally the facts of the present and past distribution of 

 animals over the earth's surface reveal such striking conditions 

 of close animal relationships accompanying the present or past 

 continuity of land and water masses, and such wideness of 

 relationship associated with long separated regions, that only 

 the explanation of evolution is sufficient to account for these 

 facts. In Australia, which is a great land mass long separated 

 geographically from other continents, the animals, except such 

 kinds as are spread by man unwittingly or intentionally, or 

 are easily distributed by ocean currents, are of kinds very 

 different from those elsewhere in the world. But in Africa 

 and South America, which are more widely separated geo- 

 graphically but have been connected in geological periods not 

 so very remote, there are many fairly close relationships among 

 the animals of the two regions. The differences, also, are just 

 about as great as the length of time of the actual separation of 

 the two continents would make probable. By such zoo-geo- 

 graphic studies carried on for many kinds and groups of ani- 

 mals, and for many regions of the earth, a great army of facts 

 has been collected which correspond perfectly with the theory 

 of descent, i.e., evolution. 



