152 THE EVOLUTION OF LIVING BEINGS. 



on in different geological periods ; all we can say is that 

 migration formerly existed as it does now. 



Yet migration has been exagerated in one respect, in 

 as much, as here also, as in former theories of evolution, 

 the dogma of the single origin reigned supreme. 



So, if Primula acaulis is found in England and in the 

 Tirolese Alps, it is concluded that it must necessarily 

 have originated either in England or in the Tirolese 

 Alps or on a single third spot from where it has migra- 

 ted to the different countries it new occupies. 



Now this creed was the consequence of the supposi- 

 tion that species arose by selection of favorable varia- 

 tions, and that, what was favorable at the one spot, could 

 not be expected to be favorable — at least not to the 

 same degree — at another spot, so that the result at 

 different spots could not be the same e. g. that the pro- 

 duction of identical species at different spots, was well 

 nigh impossible. This objection — in itself not well 

 tenable because during this selective process the ances- 

 tral species itself does not remain stationary, but also 

 migrates — of course falls away entirely if species are 

 not the result of a selective accumulation of favorable 

 variations, but are born, ready made, as a result of a cross 

 and left to try to find a place fit to support them, or. . . 

 perish. 



If we dwell a moment on the fact, that identical 

 gametes, irrespective of their source, must give the sa- 

 me kind of zygote, irrespective of the spot where the 

 mating occured, it follows from the theory of the origin 

 of newtypesbycrossing,thatidenticaltypescan originate 

 at different spots, that species can arise polytopically. 



