statistical material here brought together is fragmentary and not
entirely satisfactory, but it is sufficient upon which to base some
generalizations of scientific value. The sources of these data are
largely American. Little attempt is made to study European material,
or to discuss phases of the problem which are only of local concern.
Some topics, therefore, which have frequently been treated in
connection with the general subject of consanguineous marriages are
here ignored as having no scientific interest, as for instance that of
the so-called "marriages of affinity," which has been so warmly
debated for the past fifty years in the British Parliament.

For obvious reasons it will often be impossible to distinguish between
the different degrees of consanguinity, but wherever possible the
degree will be specified. It is probable that where a number of
marriages are vaguely given as consanguineous, few are more distant
than second cousins, for in the United States especially, distant
relationships are rarely traced except by genealogists. In designating
degrees of relationship the common terminology will be used, as in the
following table, expressing, however, the rather clumsy expression,
"first cousin once removed" by the simpler form "1-1/2 cousin."

[Illustration]

By far the greater part of the literature of consanguineous marriage
is of a controversial rather than of a scientific nature, and a search
for statistical evidence for either side of the discussion reveals
surprisingly little that is worthy of the name. Yet men of high
scientific standing have repeatedly made most dogmatic assertions in
regard to the results of such unions, and have apparently assumed that
no proof was necessary. For example, Sir Henry Sumner Maine "cannot