748 General and Applied Biology 



ber of combinations possible when the germ cells of parents fuse during 

 fertilization. This, together with natural selection, he held to be suf- 

 ficient to determine which characters might arise and perish or persist 

 and consequently be transmitted to future ofTspring. 



6. Theory of Hybridization. — This theory attempts to explain how 

 evolution might occur by the appearance of characters that are new 

 by a combination of genes of organisms of the same species or more 

 rarely of organisms of different species. Hybridization between animals 

 of different species rarely occurs, although an example of such a new 

 type is the infertile mule produced by crossing a horse and an ass. 



QUESTIONS AND TOPICS 



1. (1) Explain why abiogenesis was a common belief in the past. (2) Explain 

 when and how abiogenesis was finally disproved. 



2. Explain in detail each of the theories of the origin of life on the earth. Which 

 one, if any, seems most plausible ? Why do you say so ? 



3. Explain the phrase "continuity of life." How does this influence inheritance ? 



4. From your observations, do you believe organisms descend with change, or, in 

 other words, evolve? Is there anything wrong in such belief? Why? To 

 what source or sources must we look for the causes and control of such a 

 phenomenon? Would it be desirable to have a static, unchanging world? 



5. Discuss all the evidences from the seven biologic sciences which attempt to 

 explain descent with change. Which, if any, contributes the most logical 

 evidences? 



6. What would you infer from observing the parallelism in the development of 

 vertebrate animals? 



7. ( 1 ) What does a comparative study of the hearts of vertebrates suggest to 

 you? (2) What does a comparative study of vertebrate brains suggest? 



8. Explain two of the great theories of descent with change. 



9. What is the relation of genetics to the general principle of evolution? 



10. Define Darwinism and Lamarckism. Do their theories necessarily hold true 

 today? Why do yon or do you not believe in Darwinism today? 



SELECTED REFERENCES 



Andrews: This Amazing Planet, G. P. Putnam's Sons. 



Clark: The New Evolution, Zoogenesis, Williams & Wilkins Co. 



Conklin: The Direction of Human Evolution, Charles Scribner's Sons. 



Darwin: Origin of Species by Means of Natural Selection, London, John Murray. 



Dobzhansky: Genetics and the Origin of Species, Columbia University Press. 



Florkin: Biochemical Evolution, Academic Press, Inc. 



Gamow: Biography of the Earth, Pelican Mentor Books. 



Haldane: The Causes of Evolution, Longmans, Green & Co. 



Hooton: Up From the Apes, The Macmillan Co. 



Huxley: Evolution, the Modern Synthesis, Harpers & Brothers. 



Lindsey: Evolution and Genetics, The Macmillan Co. 



Lull: Organic Evolution, The Macmillan Co. 



