ars
subjected to this supposedly potent but very mystical "molding force."
Here again Professor Thorndike's exact measurements explode the fallacy.
They are actually, measurably, less alike at the older age; their inborn
natures are developing along predestined lines, with little regard to
the identity of their surroundings. Heredity accounts easily for these
facts, but they cannot be squared with the idea that mental differences
are the products solely of early training.

5. _Differential rates of increase in qualities subject to much
training._ If the mind is formed by training, then brothers ought to be
more alike in qualities which have been subject to little or no
training. Professor Thorndike's measurements on this point show the
reverse to be true. The likeness of various traits is determined by
heredity, and brothers may be more unlike in traits which have been
subjected to a large and equal amount of training. Twins were found to
be less alike in their ability at addition and multiplication, in which
the schools had been training them for some years, than they were in
ability to mark off the A's on a printed sheet, or to write the
opposites to a list of words--feats which they had probably never before
tried to do.

This same proposition may be put on a broader basis.[37] "In so far as
the differences in achievement found amongst a group of men are due to
the differences in the quantity and quality of training which they had
had in the function in question, the provision of equal amounts of the
same sort of training for all individuals in the group should act to
reduce the differences." "If the addition of equal amounts of practice
does not reduce the differences found amongst men, those differences can
not well be explained to any large extent by supposing them to have been
due to corresponding differences in amount of previous practice. If,
that is, inequalities in achievement are not reduced by equalizing
practice, they can not well have been caused by inequalities in previous
practice. If differences in opportunity cause the differences men
display, making opportunity more nearly equal for all, by adding equal
amounts to it in each case should make the differences less.

"The facts found are rather startling. Equalizing practice seems to
increase differences. The superior man seems to have got his present
superiority by his own nature rather than by superior advantages of the
past, since, during a period