MENTAL CHARACTERS IX MAN 



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to grant this conclusion. Holmes agrees with 

 Pearson and Heron that feeblemindedness varies 

 continuously, but he admits that this does not 

 imply " that the various kinds of mental defect are 

 not transmitted according to Mendel's law." He 

 nevertheless concludes (p. 39), '' I very much dcjubt 

 if the facts concerning the inheritance of mental 

 defect are as yet known with sufficient precision to 

 warrant our tr34ng to force them into simple Mendelian 

 formulae." We cannot agree with his statement that 

 " it seems improbable a priori that the inheritance 

 of general mental development would follow the 

 simple Mendelian formula for the inheritance of two 

 contrasted characters." All sorts of ph3^sical defects 

 in man and other animals, and in plants, are known 

 to follow the behaviour of a simple recessive character. 

 This appears to be due in each case to the fact that 

 an altered element (gene) is present in a particular 

 locus of a chromosome, and we find no difficult}' in 

 applying the same view to mental defects, which must 

 have a physical basis. 



We may, however, point out an inference which 

 follows, and has not yet been generall}^ recognised. 

 If feeblemindedness is inherited as a ]\Iendelian 

 recessive, this in itself furnishes evidence that it has 

 arisen as a defect mutation from the normal con- 

 dition. It has sometimes been suggested that feeble- 

 mindedness represents the primitive condition of 

 palseolithic man, which has persisted in certain strains 

 through crossing w^hile the gradual mental evolution 

 of the remainder of mankind has continued. If the 

 latter h3'pothesis were true, it is unlikely that simple 

 alternative inheritance would result. On the whole, 

 it appears most likely that feeblemindedness has 

 arisen many times, and may still arise, as a defect 

 mutation in various stocks, although the condition 

 itself may resemble in some respects the mental 



