families lose more
than half their numbers from it, while other families lose almost none
at all. The 10 per cent. is simply the average of all. The percentage is
high among the Irish, and low among the Jews. Life insurance companies
take consideration of this fact in examining applicants for insurance. A
family history of tuberculosis counts against even a healthy applicant,
not because of a belief that tuberculosis is directly inheritable, but
because non-resistant types, especially light-weights, are known to be
transmitted. A profound influence toward checking this malady would
evidently be exerted if the matings on the family lines exhibiting the
characteristic of susceptibility were to cease, and thus the
perpetuation of susceptible types checked.

The same is true of crime. The 80,000 prisoners constantly supported in
the United States are recruited not evenly from the general population,
but mainly from certain family breeds.[59] Criminality among "The
Jukes" is a rule, among Jonathan Edwards' descendants, the exception.
The same is true of mental abilities of different kinds. Galton showed
that the prominent English judges, statesmen, chancellors, etc., were
furnished by certain family lines only, and were not drawn evenly from
all families.[60] The same is true of feeble-mindedness.[61]

[Sidenote: Socially Noble and Ignoble Traits]

The question of what traits are desirable and what traits are
undesirable might seem, on first thought, rather a difficult matter to
determine. Few of us would like to have our neighbor's taste in the
matter constituted as a standard of judgment upon our own traits. There
is one standard of judgment, however, that is so broad and impersonal
and so founded on the elements in society to which all individuals are
subject, that it can justly serve as a line of division between the
desirability and undesirability, broadly speaking, of individual traits
for perpetuation. This is the measurement by the standard of social
worth and service commonly designated as "fitness."[62] Above this
dividing line may be roughly grouped the genius, the specially skilled,
the mediocre, who are a service to society, or at least not a burden.
Below this line may be grouped those feeble-minded, paupers, criminals,
insane, weak and sick, who are a burden, economically and socially. That
is, a person's traits are desirable of perpetuation if so balanced as to
render the individual not a burden to others.