LECTURE XXX. 



CASUAL observation of living nature and the more careful study 

 of a certain number of plants or animals cannot fail to raise the 

 question as to how the innumerable different kinds of organisms 

 came into existence. Of flowering plants alone there are more than 

 one hundred thousand species known. Of the lower plants probably 

 nearly as many are known, and it is certain that great numbers are 

 still to be discovered. 



How did all these species originate ? 



In early times the answer was given with no hesitation. Each 

 species was created at some period in the past. More recently the 

 further dogma was added, that species are immutable, i.e. are in- 

 capable of alteration through the lapse of ages. 



Finding similarities between various animals, independent minds 

 on more than one occasion, even in ancient times, suggested a re- 

 lationship between these similar forms, and more or less clearly in- 

 dicated that similar animals are similar, because they are descended 

 from a common stock. It was, however, reserved for Darwin in the 

 middle of the last century to devote himself to collecting and sift- 

 ing evidence with the set and definite purpose of establishing or 

 refuting this view. The evidence which he amassed and examined 

 led him to accept and formulate the theory of Evolution. 



The theory is of such universal application in biology and it in- 

 volves such far-reaching deductions that biologists of all kinds have 

 investigated its truth and adequacy from the most various points 

 of view, and have tested it by countless observations in the most 

 diverse branches of biology. Its sufficiency has been tried not only 

 with the facts it was formulated to explain, but also with many 

 others discovered since its enunciation. Besides this scientific en- 

 quiry it has been subjected to the most unsparing criticism of those 

 who from previous training or prejudice were hostile to the theory. 

 This controversy, in addition to sifting the evidence for and against 

 evolution, has been responsible for a vast amount of research, and 

 so has resulted in great additions to knowledge and has opened up 

 avenues to the most elevating human speculations. 



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