The material upon which this book is based is mainly derived from the
answers made to a circular sent to all the Fellows of the Royal
Society whose names appear in its Year Book for 1904.

The questions were not unreasonably numerous, nor were they
inquisitorial; nevertheless, it proved that not one-half of those who
were addressed cared to answer them. It was, of course, desirable to
know a great deal more than could have been asked for or published
with propriety, such as the proneness of particular families to
grave constitutional disease. Indeed, the secret history of a family
is quite as important in its eugenic aspect as its public history;
but one cannot expect persons to freely unlock their dark closets and
drag forth family skeletons into the light of day. It was necessary
in such a work as this to submit to considerable limitations, while
turning to the fullest account whatever could be stated openly
without giving the smallest offence to any of the persons concerned.

One limitation against which I still chafe in vain is the
impracticability of ascertaining so apparently simple a matter as the
number of kinsfolk of each person in each specific degree of near
kinship, without troublesome solicitations. It was specially asked
for in the circular, but by no means generally answered, even by
those who replied freely to other questions. The reason must in some
cases have been mere oversight or pure inertia, but to a large extent
it was due to ignorance, for I was astonished to find many to whom
the number of even their near kinsfolk was avowedly unknown.
Emigration, foreign service, feuds between near connections,
differences of social position, faintness of family interest, each
produced their several effects, with the result, as I have reason to