348 GENERAL ZOOLOGY 



generation to generation. "In this case and throughout 

 all consideration of ' evidences/ it must be remembered 

 that the evolution idea cannot be logically demonstrated. 

 It is not a simple induction from particulars, thoroughly as 

 particulars support it. It is a way of looking at the becom- 

 ing of things; and it is the only scientific modal interpreta- 

 tion that has been suggested. It is a formula that fits the 

 facts, and all the facts it fits are its ' evidences. " The 

 most recent discoveries resulting from experimental methods 

 will be discussed after the chief evolutionary theories have 

 been stated. 



THEORIES OF EVOLUTION 



Though ancient Greek scholars (Aristotle, Lucretius) 

 and others in later times (Buffon, St. Hilaire) had vague 

 evolutionary ideas, the formulation of the two leading 

 modern theories was due to Lamarck and Darwin. 



Lamarck's Theory. In the author's own words 

 "Changes in environment bring about changes in the 

 habits of animals. Changes in their wants necessarily 

 bring about changes in their habits, the new habits involve 

 the use of new parts, or a different use of old parts, which 

 results finally in the production of new organs and the 

 modification of old ones." The central idea of this theory 

 is the cumulative transmission of functional modifications- 

 use or disuse makes a particular part of an animal increase or 

 degenerate through successive generations. Lamarck fur- 

 ther affirmed, "Nature preserves everything that she has 

 caused the individual to acquire or lose by the influence of 

 the circumstances to which the race has been for a long time 

 exposed, and consequently by the predominant use of a 

 certain organ (or in consequence of its continued disuse). 

 She does this by a generation of new individuals which are 

 produced with the newly acquired organs. This occurs, 

 provided that the acquired changes were common to the 

 two sexes, or to the individuals that produced the new 

 forms." 



