PART SEVENTEEN 



EVOLUTION 



Few, if any, subjects have generated as much controversy 

 as evolution. Millions of words have been written about it, 

 starting with the early Greeks. Both scientists and clergymen 

 have touched on it. Even today, the word "evolution" is a 

 fighting word in some circles. 



Evolution usually means the development on the earth of 

 living things, from simpler forms, through time. It is a grand 

 concept, and being based upon natural laws, it is the only 

 concept that the scientist can deal with in his day by day 

 work. It should also be borne in mind that Charles Darwin 

 did not originate either the Theory of Evolution or the 

 Theory of Natural Selection. What he did was to assemble 

 a tremendous amount of data which made the Theory of 

 Natural Selection likely as the mechanism of organic evolu- 

 tion. Darwin did not know the source of the variation which 

 was the cornerstone of his theory. Today we know that varia- 

 tion originates as a result of gene or chromosomal changes. 

 There is also the feeling that some characteristics of or- 

 ganisms have no selective value, as far as we can tell, and that 

 these are passed on by chance (genetic drift). 



Another clarification that has come about in recent years 

 is the difference between speciation and evolution. The ma- 

 jor steps in phylogenetic evolution presumably occurred in 

 the Pre-Cambrian period and what has mostly happened 

 since then is speciation or the elaboration of taxa within 

 each phylum. 



In recent years, animals and plants thought extinct have 

 come to light in the living state. One is the fish known as the 

 Coelocanth and the plant is the Metasequoia. Every year wc 

 learn more and more about evolution. If the history of science 

 can tell us anything, it is that gradually we reduce the per- 

 centage of error in our theories and approach closer and 

 closer to the truth. 



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