galton.org 169
History of Twins
169
the various infantine illnesses of the children, and corresponding to each
illness was one of these halts. There remained no doubt in my mind that,
if these illnesses had been warded off, the development of the children
would have been increased by almost the precise amount lost in these
halts. In other words, the disease had drawn largely upon the capital, and
not only on the income, of their constitutions. I hope these remarks may
induce some men of science to repeat similar experiments on their
children of the future. They may compress two years of a child’s history
on one side of a ruled half-sheet of foolscap paper, if they cause each
successive line to stand for a successive month, beginning from the birth
of the child; and if they economise space by laying, not the o-inch
division of the tape against the edge of the pages, but, say, the 10-inch
division.
The steady and pitiless march of the hidden weaknesses in our
constitutions, through illness to death, is painfully revealed by these
histories of twins. We are too apt to look upon illness and death as
capricious events, and there are some who ascribe them to the direct effect
of supernatural interference, whereas the fact of the maladies of two twins
being continually alike shows that illness and death are necessary
incidents in a regular sequence of constitutional changes beginning at
birth, and upon which external circumstances have, on the whole, very
small effect. In cases where the maladies of the twins are continually
alike, the clocks of their two lives move regularly on at the same rate,
governed by their internal mechanism. When the hands approach the hour,
there are sudden clicks, followed by a whirring of wheels; the moment
that they touch it, the strokes fall. Necessitarians may derive new
arguments from the life-histories of twins.
We will now consider the converse side of our subject, which appears
to me even the more important of the two. Hitherto we have investigated
cases where the similarity at first was close, but afterwards became less;
now we will examine those in which there was great dissimilarity at first,
and will see how far an identity of nurture in childhood and youth tended
to assimilate them. As has been already
