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PROGRESSIVE DEVELOPMENT 



Am. Museum of Nat. History 



The skeleton of an amphibian dinosaur, the Brontosaurus, was unearthed in Wyoming in 

 1898. The animals shown above have been restored by placing muscles and skin over the 

 assembled skeletons. These animals probably ate soft plants and lived in shallow waters and 

 are thought to have crawled out upon land to lay eggs. 



1829), a Frenchman, set forth his ideas on evolution in his book, 

 La Philosophie Zoologique. He coined the expression use and dis- 

 use to summarize his ideas of the causes of variation in species. 

 He thought that organisms could adapt themselves to fit the envi- 

 ronment. He supposed individuals acquired the characters they 

 needed and these acquired characters were transmitted to their 

 offspring. For example, he said that the original giraffe had a 

 short neck. For some reason, it began to eat leaves from trees and 

 was constantly stretching its neck to reach them. Consequently, 

 the neck started to grow longer and the offspring were born with 

 longer necks. According to Lamarck's theory, if a man developed 

 his mind very carefully, his children would start with better minds. 

 His theory has been generally discarded. Our present knowledge 



