EVOLUTION AND HEREDITY 349 



There is no doubt that the use of particular parts makes 

 them larger or more effective and that disuse makes them 

 poorly developed and comparatively ineffective. The 

 blacksmith's arm is strong; the banker's sensitive finger 

 tips detect a spurious coin at once; the sedentary business 

 man cannot run like a savage, and the provincial peasant 

 cannot acquire broad knowledge. The chief weakness in 

 Lamarck's theory lies in the fact that such "acquired 

 characters" are not known to be transmitted in heredity. 

 The banker's children are as easily deceived by bad money 

 as was the banker before he began his training; the son of 

 the blacksmith can have powerful arms only by constant 

 exercise. In spite of this difficulty the theory, while not so 

 successful as the next, still has many warm advocates. 



Darwin's Theory. Darwin's conception of evolution 

 was that all animals and plants are subject to (1) small 

 chance variations ; thus certain individuals have a slight ad- 

 vantage over others in the (2) struggle for existence. This 

 leads to (3) natural selection by a (4) survival of the fittest, 

 and in time to the origin of new species. Darwin's theory 

 is commonly known as " Natural Selection." Though it 

 did not wholly discard Lamarck's ideas as to the trans- 

 mission of acquired characters, selection was its important 

 principle. It has been modified and supplemented some- 

 what since Darwin's time, but its chief features have stood 

 criticism remarkably well. Briefly stated, the principal 

 objections urged against natural selection are as follows: 

 (1) that it does not explain how variations that are not use- 

 ful from the beginning may be selected; (2) that variations 

 in some cases at least are most apt to take place when the 

 struggle for existence is not severe; (3) that it will not ac- 

 count for the perfection in detail which many structures 

 have attained (e.g. the wings of insects that are remarkably 

 like leaves, etc.) ; (4) that many apparently useless struc- 

 tures have developed along progressive lines; (5) that the 

 range of variation is not modified by selection; (6) that 

 chance variations cannot be the sole materials on which 



