Eugenics seeks for quantitative results. It is not contented with such
vague words as ‘much’ or ‘little,’ but endeavours to determine ‘how
much’ or ‘how little’ in precise and trustworthy figures. A simple
example will show the importance of this. Let us suppose a class of
persons, called _A_, who are afflicted with some form and some specified
degree of degeneracy, as inferred from personal observations, and from
family history, and let class _B_ consist of the offspring of _A_. We
already know only too well that when the grade of _A_ is very low, that
of the average _B_ will be below par and mischievous to the community,
but how mischievous will it probably be? This question is of a familiar
kind, easily to be answered when a sufficiency of facts have been
collected. But a second question arises. What will be the
trustworthiness of the forecast derived from averages when it is applied
to individuals? This is a kind of question that is not familiar, and
rarely taken into account, although it too could be answered easily as
follows. The average mischief done by each _B_ individual to the
community may for brevity be called _M_: the mischiefs done by the
several individuals differ more or less from _M_ by amounts whose
average may be called _D_. In other words _D_ is the average amount of
the individual deviations from _M_. _D_ thus becomes the measure of
untrustworthiness. The smaller _D_ is, the more precise the forecast,
and the stronger the justification for taking such drastic measures
against the propagation of class _B_ as would be consonant to the
feelings if the forecast were known to be infallible. On the other hand,
a large _D_ signifies a corresponding degree of uncertainty, and a risk
that might be faced without reproach through a sentiment akin to that
expressed in the maxim ‘It is better that many guilty should escape than
that one innocent person should suffer.’ But that is not the sentiment
by which natural selection is guided, and it is dangerous to yield far
to it.
There can be no doubt that a thorough investigation of the kind
described, even if confined to a single grade and to a single form of
degeneracy, would be a serious undertaking. Masses of trustworthy
material must be collected, usually with great difficulty, and be
afterwards treated with skill and labour by methods that few at present
are competent to employ. An extended investigation into the good or evil
done to the State by the offspring of many different classes of persons,
some of civic value, others the reverse, implies a huge volume of work
sufficient to occupy Eugenics laboratories for an indefinite time.