with the nature of the characteristic; degenerate
conditions of the mind, and of the delicate organs of special sense
being the most strongly intensified.

It is probable also that in the absence of degenerative tendencies
the higher qualities of mind and body are similarly intensified by
marriage between highly endowed members of the same family. Dr.
Reibmayr believes that inbreeding is necessary to the higher evolution
of the race: "A settled abode, natural protection from race mixture
and the development of a closely inbred social class are the basic
conditions of every culture period." But inbreeding must not be
carried too far: "In the course of generations the ruling class begins
to degenerate mentally and physically, until not only is the class
destroyed, but for lack of capable leadership the people (Volk) itself
is subjugated and a crossing of blood again takes place."[95]

[Footnote 95: Trans. from _Insucht und Vermischung beim Menschen_, p.
46.]

In the breeding of animals the closest inbreeding is frequently
resorted to in order to improve the stock, and many examples can be
given of the closest possible inbreeding for generations without
apparent detriment, but it is universally admitted that the animals
selected for such inbreeding must be sound constitutionally, and free
from disease. After a certain number of generations however,
degeneration apparently sets in. The number of generations through
which inbreeding may be carried varies with the species, and the
purpose for which the animals are bred. Where they are bred primarily
for their flesh, as for beef, mutton or pork, it can be pursued
farther and closer than where they are bred for achievement in which a
special strength is required--for instance in the breeding of race
horses. This would indicate that the more delicate brain and nervous
system is sooner affected than the lower bodily functions.

In man, however, freedom from hereditary taint cannot so easily be
secured. Individuals cannot be selected scientifically for breeding
purposes. Furthermore, the human body is more delicately constructed
than that of the lower animals, and the nervous system is more highly
developed and specialized, so that it is reasonable to suppose that in
man degeneration would set in earlier in the process of inbreeding,
and that it would be impossible to breed as closely as with the lower
animals. Instances are well known, however, where incestuous unions
have