on
probation he is more likely to fail, because of his own weaknesses and
his unfavorable environment. Hence the feeble-minded delinquent is much
more likely to come before the court and also to be committed to a
reformatory, jail, or industrial school than is his companion of normal
mind. Therefore practically every group of juvenile delinquents which
ultimately reaches commitment will have a very different aspect with
regard to its proportion of mental defectives from that larger group of
offenders, apprehended or non-apprehended, of which it was once a part.
In fact, it is doubtful if any group of apprehended, detained, or
probationed offenders can be said to be representative, or at least to
be exactly representative, of the true proportion of mental defectives
among all delinquents. Except where specific types of legal procedure
bring about the elimination of the defectives, it seems as if it must
inevitably result that the operation of natural selection will
continually increase the proportion of mental defectives above that
existing in the original group.

This factor of natural selection has not to our knowledge been given
adequate consideration in any published investigation on delinquency.
But if our estimate of its effects is at all justified, then most
examinations of juvenile delinquents, especially in reform and
industrial schools, have disclosed proportions of mental defectives
distinctly in excess of the original proportion previously existent
among the entire mass of all offenders. The reports of these
examinations have given rise to quite erroneous impressions concerning
the extent of criminality among the feeble-minded and its relation to
the whole volume of crime, and have consequently led to inaccurate
deductions. The feeble-minded are undoubtedly more prone to commit crime
than are the average normals; but through disregard of the influences of
this factor of natural selection, as well as of others, both the
proportion of crime committed by mental defectives and the true
proportion of mental defectives among delinquents and criminals have
very often been exaggerated.

D. ISOLATION AND NATIONAL INDIVIDUALITY

1. Historical Races as Products of Isolation[112]

The continent of Europe differs from the other great land-masses in the
fact that it is a singular aggregation of peninsulas and islands,
originating in separate centers of mountain growth, and of enclosed
valleys walled about from the