EVOLUTION— CONKI.IISr 209 



ning of this century no one had demonstrated any genetic relation- 

 ship between an}'- particular chromosome in a germ cell and any 

 particular developed character. 



Then, about the beginning of this century Professor McClung, now 

 at the University of Pennsylvania, found that an " odd " or " acces- 

 sory " chromosome is present in the males of certain grasshoppers, 

 and in one of the last cell divisions leading to the formation of 

 spermatozoa this chromosome did not divide but went into one cell 

 but not into the other and thus two kinds of spermatozoa were 

 formed, one containing the accessory chromosome and the other 

 lacking it. Since these two kinds were equal in numbers, and since 

 on the average males and females are equal in numbers, McClung in 

 1902 suggested that this accessory chromosome was the determinant 

 of sex. 



In keeping with the predominance of men, and of male psychology, 

 in science it was but natural that it should have been assumed that 

 this accessory chromosome would not be found in females and that 

 its presence in males represented the initial cause of male superiority. 

 But alas for this pleasing fiction ! Professor Wilson, of Columbia 

 University, and Miss Stevens, of Bryn Mawr College, independently 

 demonstrated in 1905 that there are two such chromosomes in the 

 females of certain insects and only one, or one and a fragment of 

 another, in males. This difference in the chromosomes of males 

 and females was later found in many other species, including man. 

 In short the male generally lacks certain hereditary materials which 

 the female possesses and instead of woman being the lesser man, as 

 Tennyson expressed it in " Locksley Hall ", man was found to be in 

 this respect the lesser woman. Thus the initial cause of sex, which 

 had been a subject of speculation for thousands of years, was found 

 in a difference in certain chromosomes in the two sexes. 



A study of the method by which the usual number of chromosomes 

 is reduced to half in the egg and sperm led to the discover}^ of the 

 causes of Mendelian heredity. In 1901 the late Prof. T. H. Mont- 

 gomery, of the University of Pennsylvania, found that chromosomes 

 of maternal and paternal origin unite in pairs just before the last 

 cell divisions leading to the formation of the sex cells, and in 1902 

 Sutton, a student of McClung's and Wilson's, discovered that cor- 

 responding chromosomes from the father and mother come together in 

 pairs, just as corresponding fingers of the right and left hands meet 

 when the hands are pressed together, thumb to thumb, index to 

 index, etc., such pairing being Imown as synapsis. In the subse- 

 quent cell division the chromosomes of each pair separate so that 

 each germ cell thus formed contains only one of the chromosomes of 

 each pair, or one-half the total number. Each of the two cells formed 



