TORREYA 



Ol. 30 XT U T^ u Nu. () 



JNovember-Uecember 



A Laboratory Lesson in Variation 



Ralph C. Benedict 



It is commonly ag eed that the essence of goo J 5ci o t 

 ing consists in 'exposirg' the student to obj'ctiv^ ealiti -, a . 

 in helpirg him to d aw his own deductions and inductions f om 

 what he observes. With respect to evolution, however is it 

 not a fact that this topic is chiefly presented and studied, at 

 least in elementary courses, through the medium of books? That 

 many learn to talk glibly regarding the 'evidences' of evolution 

 who have no real first hand acquaintance with the underlying 

 facts? A comment of the late John M. Coulter a few years ago 

 is pertinent in this connection. (Science 63: May 1926). "The 

 meaning of evolution is probably more misunderstood than 

 any doctrine of science. The reason is that it has been discussed 

 very freely by those who are not informed, and in this way 

 much misinformation has been propagated." 



It is the purpose of this article to offer an outline of a possible 

 laboratory lesson through which the most fundamental factor 

 of evolution may be presented objectively. The lesson, which 

 has been used a number of years in fourth year high school 

 biology, is based on the following premise: While all the data 

 derived from the study of the facts of morphological resem- 

 blances among related forms, of geographic distribution, of 

 geologic succession of types, of embryologic and ontogenetic 

 development, of plant breeding, etc., are valuable and impor- 

 tant as circumstantial evidence, any final understanding of the 

 basic problem of evolution must be sought in a study of variation 

 as a process. 



If the pupil can be shown that occasionally in reproduction 

 a given parent or parents produce offspring which differ from 

 the parent type, and not merely by the re-shuffling of charac- 



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