h, and Tyler)
comprise about fifty-nine per cent of the population, it will readily
be seen that comparatively few absolutely non-related marriages take
place. Yet in this community from September, 1904, to October, 1907,
or during the residence there of the present physician, Dr. P.H.
Tawes, there have been 87 births and but 30 deaths, the latter from
the usual causes. During this period there has not been a single case
of idiocy, insanity, epilepsy, deaf-mutism or even of typhoid fever on
the island.

The evidence gathered from various other isolated communities is very
conflicting. Huth describes a great many of them which have existed
for many generations without crosses without ill results. Other
writers quote instances where whole communities have become
degenerate. Until the antecedents of a community are known it is of
course impossible to estimate the effect of consanguinity. The
exceptionally high percentage of deaf-mutism on Martha's Vineyard may
to some extent be due to a high percentage of consanguineous marriage,
but that inbreeding is not the primary cause is revealed by the
records showing that among the first settlers were two deaf-mutes,
whose defect has been inherited from generation to generation for two
hundred and fifty years.[13]

[Footnote 13: See article in Cincinnati _Gazette_, Jan. 22, 1895.]

CHAPTER II

RATIO OF THE CONSANGUINEOUS TO ALL MARRIAGES

Towards determining the average frequency of occurrence of
consanguineous marriages, or the proportion which such marriages bear
to the whole number of marriages, little has as yet been done in this
country. Professor Richmond Mayo-Smith estimated that marriages
between near kin constituted less than one per cent of the total,[14]
and Dr. Lee W. Dean estimates that in Iowa they comprise only about
one half of one per cent.[15] But these estimates are little more than
guesses, without any statistical basis.

[Footnote 14: _Statistics and Sociology_, p. 112.]

[Footnote 15: _Effect of Consanguinity upon the Organs of Special
Sense_, p. 4.]

In several European countries such marriages have been registered,
though somewhat spasmodically and inaccurately. According to
Mulhall[16] the ratio of the consanguineous among 10,000 marriages in
the various countries is as follows:

TABLE I.
-----------------------------------
Country.| Ratio. | Country.| Ratio.
-----------------------------------
Prussia | 67 | Alsace