CHAPTER 26 



THEORIES AND MECHANISM 

 OF EVOLUTION 



The question as to how the present colos- uict^di^a. ^ . ^ .. 



sal array of Hving things came about has HISTORICALBACKGROUND 



puzzled man from the dawn of human in- Rudiments of the theory of organic evo- 



telligence. Civilizations of all kinds have lution can be found in writings of the early 



pondered the problem and have come up Greeks, especially Anaximander (588-524 



with some sort of answer which usually has B.C. ), Empedocles (495-435 b.c. ), and Aris- 



been incorporated into their philosophy totle (384-322 b.c). Of these,' Aristotle 



and religion. The most gratifying answer overshadowed all others because of his 



was a simple one, and to the western mind command of natural history of the world 



special creation as portrayed in the Book of of his day. He, like others of his time 



Genesis was also the most satisfactory. The believed that living things progressed from 



idea that all living things were created for simple to more complex forms, reaching the 



a purpose which they now fulfill left little pinnacle in man. In this sense his writings 



room for argument and was satisfactory for had the germ of the evolution idea but 



large segments of the populations of the beyond that they showed litde advance 



civilized world until about 100 years ago. over primitive mysticism. Unfortunately 



The belief that the earth was much older Aristode's ideas were proclaimed as dogma 



than the allotted 6,000 years ascribed by and hence the possibility of scientific rea- 



Christians did not obtain a secure foothold soning was impeded for many centuries 



until geologists began to unearth very con- His tenet was idealistic in that each animal 



vmcmg evidence confirming the antiquity was specially created in its present form, 



of the earth. Once the earth was shown to Since that fitted perfectly into the doctrines 



be very old, the history of life on it became of the churches there was no quarrel at 



an immediate and a very important prob- this early period. Historical geology had 



lem. The constant discoveries of fossil re- not yet been bom, so there could be no 



mains of plants and animals led to the con- conflict from that quarter. It was only when 



cept that life on the earth was likewise very fossils were unearthed and needed explain- 



ancient, much older than anyone had im- ing that serious clashes occurred between 



agined. With this start, the whole matter those adhering to special-creation dogma 



of the origin of living things, both past and and those willing to accept historical facts 



present, became a problem demanding of organic descent. 



careful scientific analysis. Several theories Certainly during the long period be- 

 have been advanced, the more important tween Aristotle and the Renaissance there 

 of which we shall consider after a brief must have been some brave souls who en- 

 historical background. tertained sub rosa ideas concerning the 



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