galton.org 161
History of Twins
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and the other to college, our respective characters were inverted; we both think that at that
time we each ran into the character of the other. The proof of this consists in our own
recollections, in our correspondence by letter, and in the views which we then took of
matters in which we were interested.”
In explanation of this apparent interchangeableness, we must recollect
that no character is simple, and that in twins who strongly resemble each
other, every expression in the one may be matched by a corresponding
expression in the other, but it does not follow that the same expression
should be the prevalent one in both cases. Now it is by their prevalent
expressions that we should distinguish between the twins consequently
when one twin has temporarily the expression which is the prevalent one
in his brother, he is apt to be mistaken for him. There are also cases where
the development of the two twins is not strictly pari passu; they reach the
same goal at the same time, but not by identical stages. Thus: A is born
the larger, then B overtakes and surpasses A, and is in his turn overtaken
by A, the end being that the twins, on reaching adult life, are of the same
size. This process would aid in giving an interchangeable likeness at
certain periods of their growth, and is undoubtedly due to nature more
frequently than to nurture.
Among my thirty-five detailed cases of close similarity, there are no
less than seven in which both twins suffered from some special ailment or
had some exceptional peculiarity. One twin writes that she and her sister
“have both the defect of not being able to come downstairs quickly,
which, however, was not born with them, but came on at the age of
twenty.” Three pairs of twins have peculiarities in their fingers; in one
case it consists in a slight congenital flexure of one of the joints of the
little finger; it was inherited from a grandmother, but neither parents, nor
brothers, nor sisters show the least trace of it. In another case the twins
have a peculiar way of bending the fingers, and there was a faint tendency
to the same peculiarity in the mother, but in her alone of all the family. In
a third case, about which I made a few inquiries, which is given by Mr.
Darwin, but is not included in my returns, there was no known family
tendency to the peculiarity which was observed in the twins of having a
crooked little finger. In another
