320 CONCLUDING CHAPTER 



Now we saw that there seems to be good evidence 

 that normal or continuous variations are inherited. 

 Logic does not, however, permit us to make the step : 

 Acquired variations are continuous variations; con- 

 tinuous variations are inherited ; therefore acquired 

 variations are inherited. It seems, indeed, to be this 

 fallacy which has led to the long-continued belief in 

 the inheritance of acquired characters as an important 

 factor in organic evolution, in spite of so many argu- 

 ments to the contrary. 



Formal disproof of this proposition is very difficult, 

 and in the meantime the confusion between continuous 

 acquired variations and continuous genetic variations, 

 which is always present in practice, constitutes a very 

 serious drawback to the biometric method of research. 

 At present Johannsen's explanation of these phenomena 

 seems to afford so much the simplest solution that 

 we may once more repeat his statement of the case, 

 though with the proviso that his hypothesis is not 

 universally accepted. 



Johannsen looks upon a population which, as a 

 whole, exhibits continuous or normal variability, as 

 being capable of analysis into a number of pure lines. 

 In a single pure line genetic variability is sensibly 

 absent. The members of such a pure line exhibit, 

 however, very considerable acquired variability, so 

 that in this way each line shows a normal variability 

 of its own. And the range of this variability may 

 greatly exceed the limits which separate two pure lines 

 from one another. The result is to give a completely 

 blurred picture when all the lines are looked at simul- 





