FACTORS OF ORGANIC EVOLUTION 



existence of some considerable measure of aesthetic 

 perception. There is reason to believe, however, 

 that homogamy is not conscious and deliberate, de- 

 pending upon an exercise of "taste," but is uncon- 

 scious and "instinctive." Professor Pearson has 

 been able to find record of only one research into 

 this subject besides his own; but this is directed 

 to an order of living creatures so remote from man 

 that it perhaps justifies us in drawing an inference 

 as to the existence of homogamy in intermediate 

 orders of life. The research is that of Professor 

 Raymond Pearl, of the University of Michigan, on 

 the conjugation or mating of the param&cium, 

 a unicellular animal about one-hundredth of an 

 inch in length, which no one would accuse of pos- 

 sessing high perceptive or aesthetic powers. By 

 making many thousands of careful measurements, 

 Professor Pearl has been able to show that a 

 paramcecium of a given size tends to mate with 

 another of the same size. 



The general significance of these recent biomet- 

 ric studies is very wide indeed. It is plain that ho- 

 mogamy, if indeed, as is probable, it acts through- 

 out the realm of animal life, 1 must tend to split 

 up races into endogamous groups, the individuals 

 of which marry only within the group-limit, and 



1 It will be important and necessary, I fancy, to ascertain 

 whether what we call homogamic unions tend to be more fertile 

 than those between widely different individuals. If so, it is 

 quite evident that the same principle may act in the vegetable 

 world. Professor Pearson tells me that this question has 

 scarcely been investigated. 



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