Comments on the Origin 

 and Evolution of ''Sex' 



D. H. WENRICH, Zoological Laboratory, 

 University of Pennsylvania, Philadelphia 



In the preceding discussions in this volume the reader found that 

 many variations occur in the way that "sex" expresses itself; as a 

 result, many different interpretations of its meaning and significance 

 can be offered. Here some ideas are presented which indicate that 

 there are many as yet unsolved problems in connection with "sex." 



It is difficult to give a definition of sex or of sexuality because of 

 the variations in the process and the differences of opinion about the 

 subject. In the foreword of his book on sexuality, Hartmann (Die 

 Sexualitcit, 1943) states that a controversy between certain botanists 

 and himself involved the definition of sexuality. He indicates that 

 one botanist defined fertilization and sex as the change from a hap- 

 loid to a diploid phase. Hartmann's definition was the union of two 

 sexually different haploid cells to form a diploid one. It would be 

 difficult to decide just where sexuality begins in the series of condi- 

 tions found by Cleveland for the flagellates in Cryptocerciis because 

 the change from haploidy to diploidy by one endomitotic division 

 {Barhulauyvipha) would fit into the definition of sex by the botanist 

 cited by Hartmann. Consequently, no definition of "sex" will be 

 attempted here. 



Naturally there has been much speculation about the origin and 

 evolution of "sex," most of which has been based upon conditions in 

 higher organisms. Geddes and Thomson (1889) in their book on the 

 evolution of sex made the following statement (p. 117): "The num- 

 ber of speculations as to the nature of sex has well-nigh doubled 

 since Drelincourt, in the last century, brought together two hundred 

 and sixty-two 'groundless hypotheses,' and since Blumenbach quaintly 

 remarked that nothing was more certain than that Drelincourt's own 

 theory formed the two hundred and sixty-third. Subsequent investi- 

 gators have, of course, long ago added Blumenbach's ''Bildungstrieb^ 



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