An Introduction to a Biology 



If individuals from necessity are treated collectively, it must 

 be proved that their composition is identical. In direct 

 contradiction to the methods of current statistics, Mendel 

 saw by sure penetration that masses must be avoided." 



There is one direction in which my parallel may seem 

 at first sight to be incapable of being pushed very far ; it 

 may be urged that we never can have any knowledge of 

 the individual, but only of kinds of individuals, because in 

 single cases it is impossible to eliminate the attributes which 

 are due to chance ; so that Mendelian methods are more to 

 be compared with chemistry, which tests the property, not 

 of units, but of masses of units which are known to be all 

 the same. 1 But this fact does not in the least lessen the 

 closeness of the parallel, for we have no reason to believe 

 that the demon, if his attributes are as " essentially finite 

 as our own," would have or need any knowledge of the 

 individual molecules, but merely the ability to classify them 

 into, say, ten classes, ranging from very fast to very slow, 

 and to close his door according to their speed and direction. 

 This point does not seem to be of much importance, but I 

 did not wish, by not referring to it, to appear to have over- 

 looked it. 



One result, which seems to me to follow naturally from 

 the truth of my comparison, is that it is unreasonable to 

 apply, as has often been done, the criteria of either theory 

 to a set of facts in which the conditions, on which that theory 

 is true, do not obtain ; and the manner in which materials 

 for the study of heredity are collected by Mendelians is so 

 different from those employed by biometricians that this is 

 very rarely, if ever, the case. 



From this it follows that the naturalist who sets out to 

 attack the problem of heredity will not as in the past collect 

 his facts and then see whether they fit the one theory or 



1 Cf. " The breeding-pen is to us what the test-tube is to the chemist " 

 same Address, p. 409, first column ; and cf. " Reports to Evol. Com- 

 Koyal Soc.," I., p. 159. 



158 



