10 ORTHOGENETIC EVOLUTION IN PIGEONS. 



The new species arises from the old, but without any visible preparatory steps 

 and without intermediate connecting stages. Like the old, it is subject to varia- 

 tion, but as a type it is essentially immutable. Do Vries does not deny that varia- 

 tion produces what may appear to be transitional forms, but he maintains that 

 these forms in reality have no such meaning. They are to be regarded as phenomena 

 of " transgressive variability," which may obscure but not obliterate the specific 

 limits. De Vries states (vol. 1, page 362) : 



The transitions do not appear before the new species, at most only simultaneously 

 with this, and generally only after this is already in existence. The transitions are there- 

 fore not intermediates or preparations for the appearance of the new forms. The origin 

 takes place, not through them, but wholly independently of them. 



Granting that the position with respect to the mutants obtained from the 

 evening-primrose (Oenothera lamarckiana) is unassailable, does it follow that all 

 new species have arisen by mutation and that continuous variation has never had, 

 and never can have, anything to do with the origin of species? Plausible as is the 

 argument and impressive as is the array of evidence presented, I can but feel that 

 there are reasons which compel us to suspend judgment for a while on this pivotal 

 point of the mutation theory. America is the original home of the evening-prim- 

 roses, and it is here that the natural history of the group remains to be worked out 

 in the light of the experimental results obtained in Holland. 



What does it mean that a few' mutants keep on reappearing year after year, 

 and that even the mutants themselves mutate, not in new lines, but in the same old 

 ones? Persuaded as deeply as I am that we can never draw from a species anything 

 for which no ancestral foundations preexist, I anticipate that our wild evening- 

 primroses have revelations to make. 3 Whatever revelations may await future 

 investigation in this field, the work done in the primrose garden of Amsterdam will 

 stand as a classical contribution to the new biology and as one of the very best 

 models in method of research that we have yet seen. 



Natural selection, orthogenesis, and mutation appear to present fundamental 

 contradictions, but I believe that each stands for truth, and that reconciliation is 

 not distant. 



The so-called mutations of Oenothera are indubitable facts; but two leading 

 questions remain to be answered: First, are these mutations, now appearing, as 

 is claimed, independently of variation, nevertheless the product of variations that 

 took place at an earlier period in the history of these plants? Secondly, if species 

 can spring into existence at a single leap, without the assistance of cumulative 

 variations, may they not also originate with such assistance? That variation does 

 issue in new species, and that natural selection is a factor, though not the only 

 factor, in determining results, is, in my opinion, as certain as that grass grows, 

 although we can not see it grow. 



Furthermore, I believe I have found indubitable evidence of species-forming 

 variation advancing in a definite direction (orthogenesis), and likewise of varia- 

 tions in various directions (amphigenesis). If I am not mistaken in this, the 

 reconciliation for natural selection and orthogenesis is at hand. 



» This was written (1904) before the publications of Davis and of Jeffrey on the (Enoihera.— Ed. 



