SOURCES OF CHANGE 63 



the present his conclusion is a wholly satisfactory 

 expression of our knowledge: "Since it is pres- 

 ent ... in living things generally, it may be 

 considered to be one of the original properties of 

 life, and our inability to explain its origin is not 

 different from our inability to explain the origin of 

 metabolism, reproduction, irritability, or of life 

 itself." 



The nature of its results and its immediate 

 causes are varied, and as a result many errors have 

 crept into the discussion of acquired characters. 

 Mutilations, for example, have been the subject 

 of many pages of wasted effort. They are acci- 

 dents. No thinking scientist would give them 

 serious attention in the critical study of evolu- 

 tionary processes, yet they have had a prominent 

 place in the older literature of evolution. I have 

 previously discussed this point in greater detail, 

 showing that other modifications, such as the 

 flattening or constriction of the skull by artificial 

 means in infancy are of similar nature. ^^ All of 

 these changes are impressed upon the organism 

 by the external environment. The organism is 

 unfortunate enough to get in the way of a train 

 or a sword or an amputating knife and thereby 

 loses something which it cannot replace, or its 

 parents bind its feet, and in spite of a noble struggle 

 its body is prevented from gaining normal expres- 



" Am. Nat, Vol. LXI, pp. 251-265, 1927. 



