348 BIOLOGY 



in the excellently adapted internal skeleton which the higher 

 vertebrates possess to-day. All of this can be followed out in 

 the study of fossils, and it represents only one of the many 

 series of evolutionary changes which have occurred in the history 

 of animals, adapting the race little by little to new conditions, 

 or better adapting them to older ones. 



Forces Producing Race Adaptation. While biology has not 

 yet reached a point where it considers itself capable of explaining 

 all of the marvelous phenomena of adaptation, some of the laws 

 that have been concerned in the production of the phenomena 

 are fairly well understood. A primary one seems to be the law 

 of natural selection, first exploited by Charles Darwin. This 

 law and its action will be considered on a later page. 



THE THEORY OF EVOLUTION 



The divergence of animals and plants from common centers 

 to produce the diversified world of to-day has been generally 

 known under the phrase, the theory of evolution, or the theory 

 of organic descent. The term "evolution" has a very much 

 wider application than that which has just been given to it, 

 since in its philosophical import it involves much more than the 

 problem of the origin of species of animals and plants. The 

 general theory of evolution includes the conception of the orderly 

 development of the whole universe, by a system of natural law 

 and force, and assumes that the origin of the world from the 

 original nebulous mass has been, from the beginning, due to 

 the unfolding of natural law. With the philosophical aspects 

 of the theory we are not here concerned; but the phase of the 

 theory that concerns the origin of modern animals and plants 

 is one of the fundamental factors of modern biological thought. 

 Indeed, it may be stated that modern biology did not have any 

 real existence until, under the influence of the writings of Charles 

 Darwin, the conception of the origin of species from common 

 types began to be studied. 



The idea which has been expressed above, that the adaptation 



