560 



The Earth and Its Inhabitants Change unit x 



origin of species. Lamarck suggested 

 that an organ changes according to the 

 amount it is used and that this change 

 could be inherited. He made much of 

 the terms "use and disuse." This is the 

 name giv^en to his theory. It is true that 

 a muscle, for example, becomes larger 

 through use and smaller through dis- 

 use. Lamarck believed that this charac- 

 ter of larger or smaller muscle resulting 

 from use or disuse could be inherited. 



We now know that such acquired 

 characters are not inherited. But La- 

 marck, who lived long before Weis- 

 mann, did not know that acquired char- 

 acters are not inherited. He believed 

 that if the changes were small and if 

 they continued over long periods of 

 time, the small changes would accumu- 

 late and thus a new species would ap- 

 pear. If Weismann was correct in stat- 

 ing that acquired characters cannot be 

 inherited, Lamarck's theory cannot be 

 accepted as an explanation of new spe- 

 cies. While biologists are still perform- 

 ing experiments to determine whether 

 an acquired character can ever be in- 

 herited under any circumstances, most 

 biologists believe that there is little or no 

 evidence for it. Lacking the proof that 

 acquired characters can be inherited, 

 Lamarck's theory is not satisfactory. Do 

 you understand his theory? See Exer- 

 cise 7. 



Protective resemblances and adapta- 

 tions. J\lany plants and animals are aston- 

 ishingly fitted, or adapted, to their en- 

 vironment. Because of their structure, 

 their coloring, or their behavior, some 

 animals resemble their environment so 

 closely that it is difficult to see them. 

 This is called protective resemblance, 



Fig. 510 Spnice grouse on the ground. Of what 

 advantage are the mottled brown markings on 

 the feathers? (American museum of natural 

 history) 



Fig. 511 Find the geomctrid y/ioth caterpillar 

 in the photo. It is the color of a twig. It holds 

 itself at this angle all day. It moves and feeds at 

 night. How can we explain such behavior? 



(AMERICAN MUSEUM OF NATURAL HISTORY) 



