196 UNIVERSITY OF MISSOURI BULLETIN 



The continued solution of problems in heredity will be 

 productive of important results in the modifying of our con- 

 ceptions regarding the causes of evolution in nature and in 

 guiding our attempts to direct the evolution of domesticated 

 plants and animals along the lines necessary for man's welfare. 

 Whatever may be one's convictions regarding the handling of 

 defective individuals in the humankind, we must all agree 

 that the problem is an important one and that only by ascer- 

 taining the laws by which heredity works in man can we 

 make a real beginning in the fundamental improvement of 

 our race. 



THE DETERMINATION OF SEX 



As another illustration from the field where the experi- 

 mental method is being vigorously applied we may refer to 

 the problem of the Determination of Sex, a question which has 

 attracted a large amount of attention for a long period. 

 Blumenbach at the close of the eighteenth century cited some 

 two hundred and sixty groundless hypotheses which had been 

 brought forward even up to that date. In our own day, the 

 prevailing view has been, until recently, that the sex of an 

 animal could be determined by differences in the nutrition 

 during embryonic life. This belief was based, first, upon 

 statistics drawn from the human birth rate in periods follow- 

 ing war and other hard conditions, interpreted as meaning 

 poor nourishment for a large proportion of the population, 

 and, second, upon experiments with amphibia and insects. 

 The sex was thus supposed to be determined only at a com- 

 paratively late period of embryonic life and to be mainly a 

 matter of nourishment, a rich diet producing a high per- 

 centage of females and a poor diet males in excess. 



Repetition of the experiments upon which these conclu- 

 sions were based has not given the previously claimed results ; 

 and the statistics of the human birth rate are not adequate 

 for any safe generalizations. Coincident with this has come 



