likely to be thrown into closer contact, and to feel better acquainted
with those who bear the same surname with himself. But since the
theoretical ratio would be about 1/4 it would hardly be safe to put
the probable ratio higher than 1/3, or in other words four first
cousin marriages to every same-name first cousin marriage. Our
revised formula then is:

All same-name marriages 3 1
--------------------------- = --- X --- = .75
All first cousin marriages 1 4

Instead of Mr. Darwin's .35.

Taking then the 10,198 marriages, with their 2.07 per dent of
same-name marriages, and dividing by .75 we have 2.76 per cent, or 281
first cousin marriages.

In order to arrive at approximately the percentage of first cousin
marriages in a nineteenth-century American community I counted the
marriage licenses in Ashtabula County, Ohio, for seventy-five years,
(1811-1886). Out of 13,309 marriages, 112 or .84 per cent were between
persons of the same surname. Applying the same formula as before, we
find 1.12 per cent of first cousin marriages, or less than half the
percentage found in eighteenth-century New York. This difference may
easily be accounted for by the comparative newness of the Ohio
community, in which few families would be interrelated, and also to
that increasing ease of communication which enables the individual to
have a wider circle of acquaintance from which to choose a spouse.

Adopting a more direct method of determining the frequency of cousin