170 Animal Life and Intelligence. 



which has divided into two halves, each of which has given- 

 rise to a distinct individual ; the latter from two different 

 ova. Mr. Galton collected a large mass of statistics con- 

 cerning twins of both classes. The result of this analysis 

 seems to be that, in the case of "identical twins," the 

 resemblances are not superficial, but extremely intimate;, 

 that they are not apt to be modified to any large extent 

 by the circumstances of life ; that where marked diversity 

 sets in it is due to some form of illness ; and, on the whole, 

 that innate tendencies outmaster acquired modifications.. 

 *' Nature is far stronger than nurture within the limited 

 range that I have been careful to assign to the latter." On 

 the other hand, speaking of dissimilar twins, Mr. Galton 

 says, *'Ihave not a single case in which my correspondents 

 speak of originally dissimilar characters having become 

 assimilated through identity of nurture." *' The impres- 

 sion that all this evidence leaves on the mind is one of 

 some wonder whether nurture can do anything at all,, 

 beyond giving instruction and professional training.'* 

 '* There is no escape from the conclusion that nature pre- 

 vails enormously over nurtm-e where the differences of 

 nurture do not exceed what is commonly to be found among 

 persons of the same rank of society and in the same 

 country." * 



Combining the results of Messrs. Lane and Galton,. 

 we may say that it requires persistent and long-continued 

 influence to modify the individual, and change, even by a 

 little, the structure inherited or given by nature ; but that 

 if this structure is thus modified, there may be a tendency 

 for such modification to increase by hereditary summation 

 of effects. We require, however, further and fuller observa- 

 tions to render the evidence of such hereditary summation 

 to any extent convincing. 



Turning now from the evidence afforded by man f to- 



* Francis Galton, " Inquiries into Human Faculty," p. 21 G. 



t That the epidermis is thicker on the palms of the hands and the soles 

 of the feet in the infant long before birth, may be attributable to the inherited 

 effects of use or pressure. It can hardly be held that the thickening of the 

 skin in these parts is of elimination value. 



