Pebbuary 16, 1906.] 



SCIENCE. 



247 



that his studies of plants have been mainly 

 with species as modified by man rather 

 than with species in a state of nature. For 

 instance, he says : ' ' The same original form 

 can in this way give birth to numerous 

 others, and this single fact at once gives an 

 explanation of all those cases in which spe- 

 cies comprise numbers of subspecies, or 

 genera large series of nearly allied forms. ' ' 

 In the present connection it is necessary to 

 notice only two of the fallacies embodied 

 in this sweeping assertion— the two con- 

 cerning subspecies. As a matter of fact, 

 siibspecies in nature do not occupy the 

 same ground with the parent form, but an 

 adjacent area; hence it is hard to see how 

 they could fulfil his geographic require- 

 ment, which is that forms arising by muta- 

 tion occur side by side with the original 

 stock. And since subspecies diflier from 

 the parent form only by small differences, 

 how can they arise from sports, which are 

 distinguished from the parent form by 

 large differences— differences of at least 

 specific value? 



From this it appears that de Vries's con- 

 ception of subspecies and their relations in 

 nature is somewhat hazy. In order to 

 understand the relations and mode of origin 

 of subspecies it is necessary to study them 

 on the ground where they are formed, 

 which means that it is necessary to con- 

 sider them geographically. To do this in- 

 telligently one must study species in a 

 region large enough to embrace belts of 

 transition from one faunal (or floral) area 

 to another, for it is in these transitional 

 belts that the changes from one species or 

 subspecies to another take place. The fail- 

 ure to recognize this simple but all impor- 

 tant fact accounts for most of the current 

 misconceptions concerning subspecies.^ 



, ° For present purposes it is immaterial whether 

 subspecies are based on actual known intergrada- 

 tion (the point of view of the A. O. U. Code of 

 Nomenclature) or on degree of relationship (the 



DO SPECIES ARISE INDEPENDENTLY OF GEO- 

 GRAPHIC ISOLATION? 



According to de Vries: "We must con- 

 clude that new species are produced side- 

 ways by other forms, and that this change 

 affects only the product and not the pro- 

 ducer." Two of his seven 'laws' relate to 

 this phase of the subject. These are : ' (1) 

 New elementary species appear suddenly, 

 without intermediate steps ; (2) they spring 

 laterally from the main stem (not replacing 

 it).' In thus burdening his mutation the- 

 ory with the additional requirement that in 

 giving off new forms the old is not altered, 

 but continues to exist side by side with the 

 new, he restricts its application to an ex- 

 ceedingly small number of cases, thereby 

 materially weakening the theory itself. 

 For in the case of the birth of a new species 

 the new quality or character may be either 

 neutral or beneficial. If neutral— of no 

 value to its possessor— it is conceivable that 

 the resulting new species may continue to 

 exist in the same area with the old; but if 

 beneficial the new species in the struggle 

 for existence will eventually destroy and 

 supplant the old— unless it diverges geo- 

 graphically so as to inhabit a separate area. 



Dr. D. S. Jordan has recently expressed 

 the belief that well-defined species arise 

 only as a result of geographic isolation, but 

 I am not sure that he means by this just 

 what the reader might infer. His words 

 are : "It is now nearly forty years since 

 Moritz Wagner first made it clear that geo- 

 graphical isolation was a factor or condi- 

 tion in the formation of every species, race 

 or tribe of animal or plant we know on the 

 face of the earth. This conclusion is ac- 

 cepted as almost self-evident by every com- 

 petent student of species or of the geo- 

 graphical distribution of species. ' ' A little 



point of view of the niorphologists and of some 

 systematists), the material point being that they 

 must be closely related to the parent form — either 

 directly, or indirectly through other subspecies. 



