hat mental traits will also, mental traits being ultimately
dependent on the brain and the nervous system, which are both
affected by ancestry.

[Footnote 1: These facts are based on the reports of Karl Pearson
in his _On the Laws of Inheritance in Man_. What is meant by
coefficient of correlation may be explained as follows: If the
coefficient of correlation between father and son is .3 and the
coefficient of correlation between brother and brother is .5 we
may say: a son on the average deviates from the general trend of
the population by .3 of the amount of his father's deviation, a
brother by .5 of the amount of his brother.]

Measurements of measurable traits and observations of less
objectively measurable ones, have revealed that immediate
ancestry is in itself an influential factor in producing likenesses
and differences among men with respect to mental traits.
One interesting case, interesting because it was a test of a
capacity that might be expected to be largely environmental
in its origins, was that of the spelling abilities of children in
the St. Xavier School in New York. Thorndike thus reports the test:

As the children of this school commonly enter at a very early age,
and as the staff and the methods of teaching remain very constant,
we have in the case of the 180 brothers and sisters included in the 600
children closely similar school training. Mr. Earle measured the
ability of any individual by his deviation from the average for his
grade and sex, and found the co-efficient of correlation between
children of the same family to be .50. That is, any individual is on the
average fifty per cent as much above or below the average for his age
and sex as his brother or sister.

Similarities in home training might theoretically account for this,
but any one experienced in teaching will hesitate to attribute much
efficacy to such similarities. Bad spellers remain bad spellers though
their teachers change. Moreover, Dr. J. M. Rice in his exhaustive
study of spelling ability found little or no relationship between good
spelling and any one of the popular methods, and little or none
between poor spelling and foreign parentage. Yet the training of a
home where parents do not read or spell the language well must be a
home of relatively poor training for spelling. Cornman's more careful
study of spelling supports the view that ability to spell is little
influenced by such differences in school or home training a