THE PRESENT POSITION Oh' THE THEORY OF ORGANIC EVOLUTION. 105 



If, however, we raise a progeny from a single bean produced 

 by the self-fertilization of a single bean plant, then again we 

 find that the progeny sorted by size will give rise to a curve of 

 error, lint if we now select the larger beans from this progeny 

 and raise offspring from them, we find that they vary about a 

 mean, which is not the size of their immediate parent, but is a 

 fixed mean, which is the same as that for the progeny of the 

 smaller beans. The variations in size seem therefore to be 

 fluctuations and in no way indicative of a change in hereditary 

 potentiality, and a change in type of such a line by the 

 continual selection of the larger individuals for propagation 

 would seem to be impossible. 



The same result has been arrived at by Agar, working on the 

 eggs of the water-flea Daphnia, which develop partheno- 

 genetically, and by Jennings, who studied the unicellular animal 

 Paramecium, which propagates itself by division. 



It would seem, therefore, that this work leads to the conclu- 

 sion that a very essential part of Danvin's reasoning is unsound, 

 for it would appear that by a continual selection of individuals 

 showing a certain character in greater or less degree — and this is 

 what Darwin postulated — no change in the type can be effected. 



Before, how r ever, we resign ourselves to this conclusion, there 

 are several matters which call for grave consideration. In the 

 first place, no one doubts that when two races differing from 

 one another in a sharply marked character are crossed, the 

 progeny will inherit the qualities of the parents according 

 to the laws worked out by Mendel. In broad outline this 

 was known to Darwin, who knew nothing of Mendel or of 

 his work. But it is to be remembered that Mendel expressly 

 excluded from his purview "all qualities of a more or less 

 description," and he never hinted that the laws which he 

 discovered would apply to them. Yet it is precisely these 

 qualities of "more or less" which are important to the com- 

 parative anatomist. Allied species and genera differ from one 

 another not so far as can be seen in the presence or absence of 

 a factor, but usually in the greater or less development of 

 homologous organs. These greater or lesser developments stand, 

 in many cases, in obvious relationship to the possessor's func- 

 tions and habits, and it is this adaptation which Mendel utterly 

 fails to explain. Again, while it is true that cultivated white 

 sweet-peas differ from the wild stock in the absence of a factor 

 which would allow, if present, of the production of the original 

 purple colour, the difference in size of the pod and pea in the 

 cultivated and wild varieties cannot thus be accounted for. It 



