i 3 4 THEORIES OF HEREDITY 



The germ-plasm A* is carried on in C and ex hypothesi 

 would, in the mature offspring, develop into germ-cells 

 with a tendency to divide like those of the parent and 

 to produce ' identical ' twins. It is, however, necessary 

 to bear in mind the effects of union in fertilization with 

 a germ bearing different tendencies, as well as the changes 

 introduced by the preparation for fertilization. 



The amount of resemblance between ' identical ' twins 

 has been shown by Galton, 1 who traced the after-life of 

 about eighty as far and as completely as possible, obtain- 

 ing instructive details in thirty-five cases. Of the latter 

 there were no less than seven examples ' in which both 

 twins suffered from some special ailment or had some 

 exceptional peculiarity'; in nine cases it appeared 'that 

 both twins are apt to sicken at the same time ' ; in eleven 

 cases there was evidence for a remarkable association of 

 ideas ; in sixteen cases the tastes and dispositions were 

 described as closely similar. These points of identity 

 are given in addition to the more superficial indications 

 presented by the failure of strangers or even parents to 

 distinguish between the twins. 



When the lives of twins were followed in after years 

 ' in some cases the resemblance of body and mind con- 

 tinued up to old age, notwithstanding very different 

 conditions of life'. In other cases 'the parents ascribed 

 such dissimilarity as there was wholly, or almost wholly, 

 to some form of illness '. 



The conclusions of the author are as follows: — ' Twins 

 who closely resembled each other in childhood and early 

 youth, and were reared under not very dissimilar con- 

 ditions, either grow unlike through the development of 

 natural characteristics which had lain dormant at first, 

 or else they continue their lives, keeping time like two 

 watches, hardly to be thrown out of accord except by 

 some physical jar. Nature is far stronger than nurture 

 within the limited range that I have been careful to 

 assign to the latter.' And again, ' where the maladies 

 of twins are continually alike, the clocks of their two 

 lives move regularly on, and at the same rate, governed 



1 Journal of the Anthropological Institute, 1875, pp. 324 and 39 r. 



