30 MODES OF RESEARCH IN GENETICS 



consequences of a particular hypothesis with the 

 observed data does not prove, in the absence of an- 

 other kind of evidence, that the hypothesis ex- 

 presses the causal basis of the phenomena. If an 

 hypothesis is true its numerical consequences must 

 accord with observation : but the converse proposi- 

 tion that because there is agreement the hypothe- 

 sis must be true, does not necessarily follow. It 

 is one of the weaknesses of the human mind to fall 

 into the error of thinking that it does : it is a mis- 

 take most of us have made in one form or another. 1 

 Bateson's reduplication hypothesis seems to 

 furnish an excellent concrete illustration of the 

 point. Essentially the only evidence in favor of 

 the hypothesis is that derived from the agreement 

 between observed and expected statistical ratios. 

 This is totally inadequate to base any cytological 

 hypothesis upon. Some other kind of evidence 

 must be forthcoming before it can be demonstrated 

 that some gametes "reduplicate" to a just-suffi- 

 cient degree to meet the exigencies of the case. 

 An ingenious mathematician could probably frame 



1 One learns to be cautious about "expectations." There once 

 came to my attention some results put together by a non-mathe- 

 matical biologist, who had elaborated a very complicated mathe- 

 matical hypothesis to account for his observations. The agreement 

 was wonderfully close between "observed" and "expected." Some 

 of its significance disappeared, however, when it was found, upon 

 analysis of the hypothesis, that the mathematical methods involved 

 were such that, barring an arithmetical error, there could by no pos- 

 sibility ever be more than a fractional discrepancy between observation 

 and calculation, whatever the nature of the observations I 



