CHAPTER XVI 

 PHYLOGENY 



The phylogenetic relationships of organisms and the origin 

 of species have long been topics of more than ordinary interest to 

 the scientists. In one of the most generally maintained of the 

 early conceptions, all relationship was denied because it was 

 thought that each species represents an independent, super- 

 natural creation. Such was the belief of even so recent a scien- 

 tist as Linnaeus whose systematic arrangement and classification 

 of plant and animal forms furnish one of the best clues to an 

 interpretation of the relationships of many groups. The natural 

 origin of species from preexisting forms of life was first given 

 strong support through the careful observations and generaliza- 

 tions of Charles Darwin, whose book "The Origin of Species" 

 (1859) has probably been more discussed than any other scientific 

 work. With the establishing of a belief in blood relationship 

 between the various animals a new interest in the tracing out 

 of that relationship became awakened. 



At the present time there is much ground for lack of agreement 

 concerning how species have come into existence, but among 

 scientists there is no longer any doubt that species, genera, 

 and even phyla have moved in a continuous procession since the 

 inception of life upon this planet. Even a cursory survey of the 

 evidences from paleontology reminds one of the facts that there 

 are no indications of vertebrates existing upon the earth prior 

 to the Lower Cambrian period of the earth's history and that 

 in general the faunas of successive periods and eras show advance- 

 ment beyond, yet undeniable relationships with, the preexisting 

 life. It is not the purpose of this chapter to prove the ideas of 

 continuity, development, and differentiation of living organisms, 

 for this is now accepted by those who take the trouble to examine 

 the evidences as little less than axiomatic. Nor yet is it the 

 intention to speculate upon the methods or processes whereby 

 these changes in the fauna and the creation of different types 

 have come about. Even among the best informed scientists 

 there is yet lack of unanimity of opinion upon these subjects. 



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