l6o THE FOUNDATIONS OF ZOOLOGY 



For more than fifteen hundred years men of the most acute and 

 well trained intellect devoted their lives to efforts to find out in what 

 sense a type exists, as contrasted with the individuals which exhibit 

 it; yet the modern zoologist still finds himself face to face with this 

 old problem, which, when analyzed, proves to be the same as the 

 question : What is the cause of nature ? 



The great intellectual difference between the schoolmen of the 

 Middle Ages and the man of science seems to me to be this : tha 

 the modern student has at last come to see clearly that we find i 

 nature no ultimate explanation of types ; and no reason to believ 

 that there is anything in nature which does not conform to statistical 

 laws and exhibit types. 



Statistical science, like all other branches of science, helps us to 

 regulate our actions and to act with wisdom and prudence, by mak- 

 ing known to us that order of events which makes up the system of 

 nature ; but discovery that events do take place in order is no reason 

 why they should, or even why they should take place at all. The 

 problem of the zoologist is not the existence of types, but the fitness 

 of living types for the world around them, and to my mind the 

 problem of the ** origin of species," as the zoologist understands 

 these words, would be greatly simplified if we clearly recognize the 

 fact that science holds out no well-grounded hope for any final 

 explanation of " species," in the logical sense of the word ; for while 

 we may prove that the occurrence of types is no more nor less than 

 might have been expected, this cannot show us why the thing we 

 expect should be the thing which comes about. 



The statistical study of vital types affords a means for studying 

 the phenomena of inheritance by the exact methods of mathematics, 

 and it is capable of yielding definite and valuable results, so far as 

 the vital phenomena which are studied can be treated as if they 

 stood alone ; but the attempt to generalize from vital statistics, and 

 to deduce general laws of inheritance from them, is attended by 

 peculiar difficulties, due in great part to the fact that the data which 

 are studied are not separable from the organism which exhibits them. 

 Stature, or size, or weight, may be treated abstractly for statistical 

 purposes, but the stature of an organism is not an abstraction, for 

 the organism is not only a bundle of properties, but a unit as well, 

 and its stature is only one of many features which are all beauti- 



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