The power by which Eugenic reform must chiefly be effected, is that of Popular
Opinion, which is amply strong enough for that purpose whenever it shall be,
roused. Public Opinion has done as much as this on many past occasions and in
various countries, of which much evidence is given in the Essay on
Restrictions in Marriage. It is now ordering our acts more intimately than we
are apt to suspect, because the dictates of Public Opinion become so
thoroughly assimilated that they seem to be original and individual to those
who are guided by them. By comparing the current ideas at widely different
epochs and under widely different civilizations we are able to ascertain what
part of our convictions is really innate and permanent, and what part has been
acquired and is transient.
It is above all things needful for the successful progress of Eugenics that
its advocates should move discreetly and claim no more efficacy on its behalf
than the future will confirm ; otherwise a re-action will be invited. A great
deal of investigation is still needed to shew the limit of practical Eugenics,
yet enough has been already determined to justify large efforts to instruct
the public in an authoritative way, as to the results hitherto obtained by
sound reasoning, applied to the undoubted facts of social experience.