THE GENOTYPE HYPOTHESIS AND HYBRIDI- 

 ZATION 1 



PROFESSOR E. M. EAST 

 Harvard University 



It sometimes seems as if the hypercritical attitude had 

 become an obsession among biologists. A proper judi- 

 cial spirit is of course essential to science, but do not 

 biologists often require a large amount of affirmative 

 data before assenting to a proposition which is in real- 

 ity a simple corollary of one already accepted? 



For example, Darwin emphasized small quantitative 

 variations as the method of evolution, although he rec- 

 ognized the occurrence of larger changes both quantita- 

 tive and qualitative. De Vries, on the other hand, 

 emphasized large variations — especially qualitative 

 variations — as the real basis of evolution, although he 

 too admitted the existence of lesser changes. He dis- 

 tinctly states that a mutation or new basis for fluctua- 

 ting variation, may be so small that it is obscured by the 

 fluctuations themselves. 



If relative frequency of occurrence is a criterion of 

 the value of variations in organic evolution, which is not 

 necessarily so, Darwin's point of view is probably the 

 nearer correct. If one could find a unit basis for describ- 

 ing variations in terms of the physiological economy of 

 the organism concerned, i. e., if one knew exactly what 

 was a large change and what was a small change, he would 

 probably find that a random sample of inherited varia- 

 tions followed the normal curve of error. By this I 



of th^Amedcan SoXt^ Naturli^ ^ 



