JOHANNSEN 



the theorv' of evolution. For a selec- 

 tion in cases such as mine is effective 

 only in so far as it selects out repre- 

 sentatives of an already existant geno- 

 type. These genotypes would not be 

 successively originated through the re- 

 tention of those individuals which vary 

 in the desired direction; they would 

 merely he found and isolated. 



The knowledge that has been gained 

 from studies on pure lines, combined 

 with a knowledge of hybridization, 

 must serve as the starting point in the 

 case of studies on heredity within 

 population in which pure lines can not 

 be completely isolated as a conse- 

 quence of the necessity of constant 

 cross-fertilization or hybridization. 

 This knowledge is, as has been pointed 

 out earlier, in complete agreement 

 with the basic ideas in the great work 

 of de \^ries— as has been seen, my con- 

 cepts have been arrived at via a some- 

 what different path than that followed 

 by de Vries, and it is also important to 

 note, based on a different kind of in- 

 formation. 



In addition the important question 

 of correlative variation takes on a 

 somewhat changed character depend- 

 ing upon whether one works with 

 pure lines or with populations. In the 

 latter case a given "ratio of correla- 

 tion" (Pearson's term) will not neces- 

 sarily represent a strongly legitimate 

 relationship, as I have sought to dem- 

 onstrate earlier. An indicated correla- 

 tive relationship is much more signifi- 

 cant within a pure line. My summation 

 table speaks very well for this concept, 

 in that it was not possible to change 

 through selection within pure lines the 

 correlation between length and width 

 of the beans, while it was simple to 

 isolate truly different genot\^pes, as for 

 example narrow and broad forms, 

 from the original population, which 

 appeared to be entirely homogeneous. 



Again, we have to, reckon with the 



25 



possibility of mutation; for thereby 

 even the strongest correlative relation- 

 ship could be destroyed. I do not wish 

 to take up this question at this time; in 

 a later publication I hope to shed more 

 light on it, using the principle of pure 

 lines as the basis for the research. 



I would be sorry indeed if the reader 

 of this work would come to feel that 

 the value of the significant work of 

 Galton, Pearson, and other biometrical 

 research workers were to be placed in 

 doubt. I would not have the audacity 

 to criticize the treatment which Pear- 

 son in particular has given to the ques- 

 tion of the ancestral influence within 

 a specific population. I do think, how- 

 ever, that the principle of pure lines 

 in the hands of a man such as Pearson 

 can carry biometric studies much far- 

 ther along than his studies of popula- 

 tions. Obviously the relationships 

 studied by Pearson have great scientific 

 significance and they have consider- 

 able practical value as well— but they 

 are not suitable to illuminate com- 

 pletely the fundamental laws of hered- 

 it)\ 



And what particularly affects Gal- 

 ton's research, in my estimation, is that 

 the results presented here support in a 

 beautiful way the basic ideas of Gal- 

 ton's "Stirp" theory,^ which was al- 

 ready worked out in 1876. This law 

 includes almost all that is of actual 

 value in the more recent Weismann 

 theory on the "Continuitv' of the 

 Gerniplasm." That the speculation of 

 Weismann ^ could overshadow the 



3 Galton's theory is known to me from his 

 original paper in Revue Scientifique, vol. 10, 

 1876, p. 198 ("Theorie de I'heredite"). 



•* The position of biometricians on "Weis- 

 mannism" has been clearly evaluated by 

 Pearson in his characterization of this move- 

 ment in "Socialism and Natural Selection" 

 {Fortnightly Review, July, 1894. Reprinted 

 in Pearson's Chafices of Death, vol. 1, 1897, 

 p. 104) . I do not plan to go further into this 

 question at this time. 



