PROBLEM 4. The Effect of the Environme?it on the Organism 491 



raised. At low temperatures the genes vironment as factors that work separately 



produce red flowers; at high temperatures in producing the organism. What is 



thev produce white flowers. That does really inherited is genes which have a 



not mean that the temperature changes tendency to produce certain effects un- 



the genes. The genes have remained un- der certain environmental conditions. If 



changed for many generations. But, evi- conditions of the environment are 



dently, these genes have different effects changed, different effects or characters 



under different environmental conditions. may be produced. The heredity and the 



What makes the individual what it is? environment act together in producing 



We must not think of heredity and en- the characters of an individual. 



Questions 



1. Why does normal sexual reproduction result in variations among in- 

 dividuals of the same species? 



2. What environmental factors may cause variations? Give examples of 

 variations in you and your classmates caused by the environment. 



3. Explain what we have learned by careful measurements about varia- 

 tions in man and in the bean. 



4. What did Lamarck notice about the effect of the environment on an 

 organism? Do you believe that acquired characters are inherited? De- 

 fend your answer. 



5. When and by whom was the phrase "continuity of germ plasm" intro- 

 duced? Explain what he meant by it. To what extent have we modified 

 Weismann's beliefs? Explain how Weismann's beliefs have led someone 

 to say: "The parent is rather the trustee of the germ plasm than the 

 producer of the child." 



6. Describe the object, the method, and the conclusions of Weismann's 

 experiment on rats. What criticisms have been made of this experi- 

 ment? 



7. Cite a fact that seems to support the idea that acquired characteristics 

 are not inherited. Explain the method and results of an experiment 

 which seems to show that acquired characteristics are not inherited. 



8. {Optional) Give three examples of genes that produce effects only in 

 special environments. 



9. What two factors are always involved in producing the characters of 



an organism? 



o 



Exercises 



I. List the factors of a child's environment which would affect it dur- 

 ing the first year of its life. List other factors besides those mentioned in 

 the text which affect you. Compare the number of factors in your en- 

 vironment with those in the environment of a young child; of a dog. 



