INHERITANCE OF MENTAL DEFECTS AND DISEASE 69 
Doubtless the writers who attribute so much to degeneracy 
have often failed to recognize traits which are separately trans- 
missible. But on the other hand, exclusive attention to the 
inheritance of particular characteristics leads to a disregard of 
other features of organisms which may be associated with the 
characters studied. Most studies made upon the Mendelian 
inheritance of human traits suffer from this drawback. Inspired 
by the desire to apply Mendel’s law to all heritable traits, Mendel- 
ians have focussed their attention almost exclusivily upon partic- 
ular characters in the hope of unravelling the complex skein of 
human inheritance by tracing out the individual traits. With 
fuller experience with Mendelian phenomena it is coming to be 
recognized by many investigators that ‘‘characters” are not 
entities by themselves, but symptoms of general and deep-seated 
though it may be slight modifications. As Dr. T.H. Morgan says: 
“‘Most students of genetics realize that a factor difference usually 
affects more than a single character. For example, a mutant 
stock [of Drosophila] called rudimentary wings has as its principle 
[principal] characteristic very short wings. But the factor for 
rudimentary wings also produces other effects as well. The fe- 
males are almost completely sterile, while the males are fertile. 
The viability of the stock is poor. When flies with rudimentary 
wings are put into competition with wild flies relatively few of the 
rudimentary flies come through, especially if the culture is 
crowded. The hind legs are also shortened. All these effects are 
the results of a single factor-difference.” Such flies may be called 
degenerates; whether they are more variable than robust races 
we do not know. 
There is no doubt that many writers of a generation or more 
ago employed the notion of degeneracy in too wide and loose a 
sense. Nevertheless there may be an important element of truth 
in the idea which is apt to be overlooked by modern geneticists in 
their preoccupation with the transmission of particular and clearly 
definable characteristics. A more critical study of degenerate 
strains of plants and animals might afford valuable suggestions 
for the interpretation of many phenomena of human heredity. 
