This has been too frequently
assumed without adequate evidence by many geneticists. It is probable
that just as the multiplicity and interrelation and minuteness of many
factors have been the principal discoveries of genetics in recent years
that the next few years will see a great deal of evidence following the
important lead of Castle and Jennings, as to variation in factors.
Knowing that all the characters of an individual are due to the
interaction of numerous factors, one must be particularly slow in
assuming that such complex characters as man's mental traits are units,
in any proper genetic sense of the word. It will, for instance, require
very strong evidence to establish feeble-mindedness as a unit character.
No one who examines the collected pedigrees of families marked by
feeble-mindedness, can deny that it does appear at first sight to behave
as a unit character, inherited in the typical Mendelian fashion. The
psychologist H. H. Goddard, who started out with a strong bias against
believing that such a complex trait could even _behave_ as a unit
character, thought himself forced by the tabulation of his cases to
adopt the conclusion that it does behave as a unit character. And other
eugenists have not hesitated to affirm, mainly on the strength of Dr.
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