THE HEREDITARY BASIS 25 



months old. Two twins at the age of twenty-three were attacked 

 by toothache, and the same tooth had to be extracted in each case. 

 There are curious and close correspondences mentioned in the 

 falling off of the hair. Two cases are mentioned of death from the 

 same disease; one of which is very affecting. The outline of the 

 story was that the twins were closely alike and singularly attached ; 

 . . . they both obtained Government clerkships and kept house 

 together, when one sickened and died of Bright's disease, and the 

 other also sickened of the same disease and died seven months 

 later." The other cases of striking resemblance given by Galton 

 and the additional data afforded by later investigators clearly 

 indicate the existence of a class of twins characterized either by 

 identical inheritance, or an inheritance so similar as to be unac- 

 countable according to the ordinary laws of hereditary transmis- 

 sion. This very close resemblance in bodily and mental states 

 commonly persists when the twins have been long separated and 

 exposed to different environments.^ 



The ordinary differences of environment met with in the life of 

 people of much the same mental status apparently fail to produce 

 changes in the personality of human beings as great as commonly 

 met with in the children of the same parents. Whatever may be 

 said of the differences which either heredity or environment 

 might produce, there are strong grounds for the statement of 

 Gal ton's "that nature prevails enormously over nurture when 

 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. My fear is, that my evidence may seem to prove too 

 much, and be discredited on that account, as it appears contrary 

 to all experience that nurture should go for so little. But expe- 

 rience is often fallacious in ascribing great effects to trifling cir- 

 cumstances. Many a person has amused himself with throwing 

 bits of stick into a tiny brook and watching their progress; how 

 they are arrested, first by one chance obstacle, then by another; 

 and again, how their onward course is facilitated by a combina- 



Additional information on the subject may be found in number 9 of the Journal 

 of Heredity (Dec, 1909), which is devoted entirely to twins. 



