INHERITANCE OF MENTAL DEFECTS AND DISEASE 35 



oped. In the Fi generation of a normal and a polydactylous 

 person the dominant character varies from complete development 

 to entire absence of visible somatic expression. In view of the 

 frequency of such facts as these, and considering also the contin- 

 uous variability in the manifestation of mental qualities in gen- 

 eral, it is inadmissible to draw the conclusion that the mating of a 

 normal person, even of sound stock, with a mental defective will 

 be productive of mentally normal ofTspring. The supposition 

 that matings of this sort are productive of offspring whose mental 

 characters tend to be more or less intermediate between those of 

 their parents, is one that is quite in accord with the large body of 

 facts that has accumulated on the inheritance of mental traits. 

 There are cases in which the mating of a person of good intelligence 

 with a person of subnormal mentality has resulted in fairly intelli- 

 gent offspring, but unions of this kind as a rule are not productive 

 of happy results. Normal progeny from such matings may repre- 

 sent cases where for some reason, the dominance of one parent is 

 unusually complete. But the many cases in which the matings of 

 normal and defective are productive of a variable degree of mental 

 defect in the offspring may be to a considerable degree the result 

 of imperfect and variable dominance. 



It has been generally assumed by a number of American work- 

 ers that where mental defectives arise from such matings the 

 apparently normal person was heterozygous. To account for the 

 large number of defectives thus arising it has to be supposed that 

 people heterozygous for mental defect are very common. In 

 Goddard's charts {Bull. Etigen. Rec. Of. No. i) out of thirty 

 matings of feeble-minded with presumably normal individuals all 

 but two produced some feeble-minded offspring. In one of these 

 (chart 6) three of the offspring, although they were marked nor- 

 mal, had feeble-minded children. In the other family the only 

 recorded mating among the presumably normal children was 

 between an alcoholic woman and a man marked normal from 

 another stock. This mating produced three normal and two 

 feeble-minded children. 



It must be borne in mind, however, that the people marked 



