marriage, I estimated in each of sixteen genealogical works, the
number of marriages recorded, and found the total to be 25,200. From
these sixteen families I obtained 153 cases of first cousin marriage,
or .6 per cent. Allowing for the possible cases of cousin marriage in
which the relationship was not given, or which I may have over-looked,
the true percentage is probably not far below the 1.12 per cent
obtained by the other method.

The compiler of the, as yet, unpublished Loomis genealogy writes me
that he has the records of 7500 marriages in that family, of which 57
or .8 per cent are same-name marriages. This would indicate that 1.07
per cent were between first cousins.

In isolated communities, on islands, among the mountains, families
still remain in the same locality for generations, and people are
born, marry and die with the same environment. Their circle of
acquaintance is very limited, and cousin marriage is therefore more
frequent. If we exclude such places, and consider only the more
progressive American communities, it is entirely possible that the
proportion of first cousin marriages would fall almost if not quite to
.5 per cent. So that the estimate of Dr. Dean for Iowa may not be far
out of the way.

Even for England Mr. Darwin's figures are probably much too large.
Applying the corrected formula his table becomes:

TABLE VI.
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|Number |Per cent of|Per cent of
1872. |marriages |same-name |first cousin