CHAPTER XIV 

 EVOLUTION 



The different kinds of animals and plants, their number and 

 distribution, are all thought to be the results of natural causes 

 collectively known as evolution. Evolution is a process of 

 change that affects everything in the universe. All matter, 

 living and nonliving, is changing continuously. In biology, 

 evolution implies descent in living things; that the living animal 

 and plant population is descended from a more primitive popula- 

 tion; that higher forms have evolved from lower forms. This 

 does not mean that the lower forms living today are in direct line 

 of ancestry of higher forms, but that they have departed to a 

 lesser degree from ancestral types common to both. Evolution 

 is in direct conflict with the idea that the various forms of life 

 known today were created as such in the beginning of the living 

 world. The theory of evolution teaches that life evolved from 

 nonliving matter, as a result of a universal process of change in 

 matter, guided or controlled to a certain extent by environment, 

 and that the first living things were relatively simple in form and 

 structure and in all probability quite unlike the living things of 

 the present time. Possibly the first living matter was not cellular 

 at all but something of the nature of a so-called living virus, such 

 as is the cause of mosaic disease in tobacco plants, referred to in 

 the previous chapter. Such hypothetical primitive forms of life 

 are thought to have gradually given rise to the various types of 

 life known today. Diversity in living things is thus the result 

 primarily of a fundamental law or condition of change. 



From the broad view of evolution not only are all animals 

 genetically related, but animals and plants as well, since the 

 differences between the lowest animals and the lowest plants are 

 bridged more or less by certain intermediate forms that combine 

 animal and plant qualities. The community of origin is recog- 

 nized in the employment of the term Protista to include all 

 unicellular forms, both plant and animal. Protista, presumably, 



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