68 Can Science Explain Life? 



Paramecium, disclose no specialization of func- 

 tion on the part of the two sexes respectively, nor 

 has it ever been shown that those unicellular or- 

 ganisms which reproduce by conjugation exhibit 

 greater variability than those which reproduce 

 asexually. 



The real reason for the existence of two sexes 

 seems to be that reduction-division followed by 

 fertilization is the only means by which it is pos- 

 sible, in nature, to bring about extensive diversi- 

 fication of tissues. In order to produce the com- 

 plex anatomical organizations of the higher 

 plants and animals, there must occur not only a 

 succession of cell divisions, but also a series of 

 alterations in the chemical structures of certain 

 of the daughter cells during early embryonic de- 

 velopment so as to produce the different types of 

 somatic cells which upon further division will 

 produce the various body tissues. These altera- 

 tions are the result of that extensive internal re- 

 organization which took place during reduction- 

 division and fertilization and seem to constitute 

 a process of readjustment by which the embryonic 

 somatic cells again return to a state of equilib- 

 rium. Such alterations are probably irreversible 

 because somatic cells can never produce germ cells 

 again, except in a few of the simplest metozoa. 

 The natural life cycle of the somatic cells is dis- 



