570 - Heredity and Evolution 



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Fig. 29-17. Mastodons were very numerous toward the end of the tertiary 

 period. (Courtesy of the American Museum of Natural History, New York.) 



rived from lower primates. In fact, when one races of man that are alive today belong to a 



traces the fossil record, it is impossible to single species, Homo sapiens: and that the 



draw a sharp line between the apes and the oldest fossil remains of this species are found 



several species of "man" that existed in the in Pleistocene strata, formed about 250,000 



Pleistocene epoch. Also it is clear that all years ago. 



TEST QUESTIONS 



1. Explain how a study of the classification of 

 a given group of organisms (for example, 

 vertebrates) leads to the conclusion that all 

 the types belonging to the group (for exam- 

 ple, fish, amphibians, reptiles, birds, and 

 mammals) are variously interrelated by de- 

 scent. 



2. List twenty features possessed by all verte- 

 brate animals but not by any other group of 

 animals. 



3. Explain how and why a biologist can predict 

 many things about an animal or plant he 

 has never seen, provided he is merely told 

 the phylum and the class of the unknown 

 organism. 



4. Specify: 



a. five human bones that have homolo- 

 gous parts in the frog's skeleton 



b. four parts of man's digestive tract for 

 which there are homologous organs in 

 the frog 



c. four parts of man's excretory system for 

 which there are homologous organs in 

 the rat 



d. five parts of man's nervous system for 

 which there are homologous parts in 

 all other vertebrates 



What is the justification for considering that 

 the arm of a man is homologous to: (a) 

 the wing of a bird; (b) the forelimb of a 

 frog? 



Explain the basis for the statement that a 

 reptile, essentially, is "a patched up and 

 made over amphibian." 



What is a vestigial structure? Mention three 

 of man's vestigial structures. How are ves- 

 tigial structures to be accounted for? 

 How does a human embryo resemble the 

 embryos of fish (and other vertebrates) in 

 regard to: 



a. origin, position, and structure of the 

 nervous system 



