PROBLEMS OF MODERN SCIENCE 



the two are fruitfully united in one individual, 

 and perhaps that explains why so many biologists 

 are apt to look a little askance at Biometrics. 

 Possibly, also, the data with which the bio- 

 metrician works are themselves too complex and 

 too lacking in precision to yield their full quota 

 of value to this method of treatment. Doubtless 

 many important results have been obtained, as in 

 the case of Johannsen's work on pure lines and the 

 attempt to distinguish sharply between mutations 

 and fluctuating variations connected therewith, 

 and the method is one which may be fruitful 

 enough in cautious and experienced hands. It 

 is not, however, for one who has no mathematical 

 capacity to speak of it, and in any case space does 

 not permit of more than a passing reference. 



We come at length to the last of our three main 

 categories Philosophical Biology, and here we 

 can afford to be very brief, for we have already 

 trespassed upon this field repeatedly. The chief 

 content of this division of our subject is undoubtedly 

 the Theory of Organic Evolution. It is safe to 

 say, as I have already indicated, that this theory 

 stands more firmly grounded to-day than at any 

 time in its past history, and that it is still the most 

 fruitful source of inspiration for the biological 

 investigator. The evidence for the evolution of 

 the whole organic world in a tree-like manner 

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