of equal advantage for all, he increases
his lead." This point has been tested by such simple devices as mental
multiplication, addition, marking A's on a printed sheet of capitals and
the like; all the contestants made some gain in efficiency, but those
who were superior at the start were proportionately farther ahead than
ever at the end. This is what the geneticist would expect, but fits very
ill with some popular pseudo-science which denies that any child is
mentally limited by nature.

6. _Direct measurement of the amount of resemblance of mental traits in
brothers and sisters._ It is manifestly impossible to assume that early
training, or parental behavior, or anything of the sort, can have
influenced very markedly the child's eye color, or the length of his
forearm, or the ratio of the breadth of his head to its length. A
measure of the amount of resemblance between two brothers in such traits
may very confidently be said to represent the influence of heredity; one
can feel no doubt that the child inherits his eye-color and other
physical traits of that kind from his parents. It will be recalled that
the resemblance, measured on a scale from 0 to 1, has been found to be
about 0.5.

Karl Pearson measured the resemblance between brothers and sisters in
mental traits--for example, temper, conscientiousness, introspection,
vivacity--and found it on the average to have the same intensity--that
is, about 0.5. Starch gets similar results in studying school grades.

Professor Pearson writes:[38]

"It has been suggested that this resemblance in the psychological
characters is compounded of two factors, inheritance on the one hand and
training and environment on the other. If so, one must admit that
inheritance and environment make up the resemblance in the physical
characters. Now these two sorts of resemblance being of the same
intensity, either the environmental influence is the same in both cases
or it is not. If it is the same, we are forced to the conclusion that it
is insensible, for it can not influence eye-color. If it is not the
same, then it would be a most marvelous thing that with varying degrees
of inheritance, some mysterious force always modifies the extent of home
influence, until the resemblance of brothers and sisters is brought
sensibly up to the same intensity! Occam's razor[39] will enable us at
once to cut off such a theory. We are forced, I think, literally forced,
to the general conclusion tha