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 
Galton’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- 
1 Additional information on the subject may be found in number g of the Journal 
of Heredity (Dec., 1909), which is devoted entirely to twins. 
