, in an unusually thorough psychological study of
1000 young adult prisoners, finds the proportion of
feeble-mindedness not far from 50 per cent.

But it is needless to multiply statistics. Those given are but samples.
Tests are at present being made in most of the progressive prisons,
reform schools, and juvenile courts throughout the country, and while
there are minor discrepancies in regard to the actual percentage who are
feeble-minded, there is no investigator who denies the fearful role
played by mental deficiency in the production of vice, crime, and
delinquency.[1]

[1] See References at end of volume.

Heredity studies of "degenerate" families have confirmed, in a striking
way, the testimony secured by intelligence tests. Among the best known
of such families are the "Kallikaks," the "Jukes," the "Hill Folk," the
"Nams," the "Zeros," and the "Ishmaelites."

_The Kallikak family._ Martin Kallikak was a youthful soldier in
the Revolutionary War. At a tavern frequented by the militia he
met a feeble-minded girl, by whom he became the father of a
feeble-minded son. In 1912 there were 480 known direct
descendants of this temporary union. It is known that 36 of
these were illegitimates, that 33 were sexually immoral, that 24
were confirmed alcoholics, and that 8 kept houses of ill-fame.
The explanation of so much immorality will be obvious when it is
stated that of the 480 descendants, 143 were known to be
feeble-minded, and that many of the others were of questionable
mentality.

A few years after returning from the war this same Martin
Kallikak married a respectable girl of good family. From this
union 496 individuals have been traced in direct descent, and in
this branch of the family there were no illegitimate children,
no immoral women, and only one man who was sexually loose. There
were no criminals, no keepers of houses of ill-fame, and only
two confirmed alcoholics. Again the explanation is clear when it
is stated that this branch of the family did not contain a
single feeble-minded individual. It was made up of doctors,
lawyers, judges, educators, traders, and landholders.[2]

[2] H. H. Goddard: _The Kallikak Family_. (1914.) 141 pp.

_The Hill Folk._ The Hill Folk are a New England family of which
709 persons have been traced. Of the married women, 24 per cent
had given birth to illegitimate