An Introduction to a Biology 



gametes ; and if an F l hybrid could multiply partheno- 

 genetically, none of its offspring would be like itself. This 

 theory as to the nature of the character-representing elements 

 borne by the hybrids is so remarkable that one requires very 

 strong evidence for it to believe it. The only evidence so 

 far adduced is that the proportions in which the various 

 kinds of young occur are those demanded by the theory ; 

 but this does not prove the theory to be true. 



The question we have to ask ourselves in considering the 

 value of the evidence for an hypothesis is not " How many 

 cases are there which are consonant with its truth ? " but 

 " Is there a single case which is not ? " The list of cases 

 in which the proportion 1:2:1 obtains in the F 2 generation 

 is lengthening every day, and it is imagined that the value 

 of the evidence for this particular theory becomes greater 

 as the list becomes longer. The simple truth that I have 

 stated in the form of two questions above is often forgotten. 



We are too apt to think that it is sufficient to rest content 

 with the many that are with us ; and too ready to forget 

 that we ought to be up and seeking out one that may be 

 against us. 



Are there any facts which render the above-outlined 

 Mendelian theory untenable ? I have at my disposal two, 

 to only one of which will I refer now. I may say, by way 

 of preface, that I do not wish my remarks to be construed 

 as antagonistic to Mendelian theory as a whole, but merely 

 critical of a particular hypothesis bearing that name, which 

 was put forward two years ago an hypothesis in which 

 Mr. Bateson ceased to believe before I did. 



At a time when I still thought that it was a useful sub- 

 ject for investigation to try to find out which of the two 

 theories, Galton's or Mendel's, fitted the result of my experi- 

 ment best, I obtained a result that was apparently conclusive 

 in favour of the former. 



The result, which I have described before, but which I 

 may briefly recapitulate here, was obtained by tabulating 



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