428 THEORIES OF EVOLUTION 



ian theory, is due to the fact that the deer-like ancestors 

 stretched and so lengthened their necks to a slight extent. 

 The immediate descendants inherited longer necks in con- 

 sequence of their parents' activity. Generation after gen- 

 eration this process of stretching and transmitting the 

 effects went on, and the increasingly long-necked species 

 evolved into the modern giraffe. 



Scientific journals and the public press recounted in- 

 stances of the (supposed) inheritance of mutilations, the 

 transmission of a powerful physique due to exercise, and 

 imphcitly or explicitly, the work of the schools, churches, 

 asylums, hospitals, and other philanthropic institutions 

 was based on the belief that the benefits conferred upon 

 one generation are inherited by the next. 



The New Lamarckian School. — Toward the close 

 of the last century, Weismann challenged this theory of 

 the inheritance of acquired characters, and demanded 

 more conclusive evidence than had hitherto satisfied the 

 scientific world. He also directed attention to the fact 

 that a modification, such as a neck lengthened by stretch- 

 ing, can only be transmitted to the succeeding generation 

 by means of the germ cells. And not only this, but the 

 Lamarckian theory requires that precisely that portion 

 of each germ cell which controls the development of the 

 neck must be changed to the exact extent required for 

 the inheritance of the modification. As a result of this 

 challenge, old evidence was carefully scrutinized and 

 found to be inconclusive. New evidence was sought, but 

 without avail. To-day there are no known cases where 

 definite, specific changes in an organism due to the influ- 

 ence of the environment on the body are inherited by the 

 offspring. 



There is evidence that the form, color, size, vitality, 

 etc., of an indivi(hial may be modified by environmental 

 influcncos, and the descendants of such parents may 

 vary more or less widely from the normal type. For ex- 

 ample, the size of seeds stands in close relation to the 



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