The Natural History of Mating. Sex, Its Nature and 

 Consequences. Sex in the Protozoa: Is Sex Coextensive 

 with Life and Necessary to Its Continuance? 



have dealt with heredity and other genetic problems 

 in the cases where there is but a single parent; we 

 now turn to reproduction where there are two parents in- 

 stead of one. The mating of two individuals that occurs at 

 times in almost all organisms is one of the most extraor- 

 dinary processes in nature; it has the effect of complicat- 

 ing tremendously all biological questions. Volumes have 

 been written as to its purpose and meaning. 



Some tell us that it is unscientific to ask as to the "pur- 

 pose" or "object" of any process; Dobell (1914) has made 

 this point with relation to all such discussions of mating. 

 The criticism is justified, so far as the method of expression 

 goes, and the literal implications of that method of expres- 

 sion; science cannot deal with purposes or ends, save in the 

 case of conscious human purposes. Nevertheless, a really 

 scientific question is often hidden under this form of expres- 

 sion. What it really means is: What difference does it 

 make whether this process occurs or not? Any question 

 as to "purpose" or "object" that can be put in this form is 

 a scientific question in spite of its teleological clothing; any 

 teleological question that cannot be put in this form is no 

 affair of science. To ask what difference this phenomenon 

 makes, leads at once to experiment; a question that could 

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