248 PROBLEMS OF GENETICS 



derivatives. We should expect such groups of forms to behave 

 like the Erophila types, and frequently to produce sterile products 

 on crossing. Whatever be the explanation, the fact remains 

 that such evidence is wanting almost completely. In spite of 

 all that we know of variability nothing readily comparable with 

 the power to produce a sterile hybrid on crossing with a near 

 ally, has yet been observed spontaneously arising, though that 

 characteristic of specificity is one of the most widely distributed 

 in nature. It may be that the lacuna in our evidence is due 

 merely to want of attention to this special aspect of genetic 

 inquiry, and on the whole that is the most acceptable view which 

 can be proposed. But seeing that naturalists are more and 

 more driven to believe the domesticated animals and plants to be 

 poly-phyletic in origin — the descendants, that is to say, of several 

 wild forms — the difficulty is proportionately greater than it was 

 formerly, when variation spontaneously occurring was regarded 

 as a sufficient account of their diversity. 



Concluding Remarks. 



The many converging lines of evidence point so clearly to 

 "the central fact of the origin of the forms of life by an evolutionary 

 •process that we are compelled to accept this deduction, but as 

 to almost all the essential features, whether of cause or mode, 

 by which specific diversity has become what we perceive it to 

 be, we have to confess an ignorance nearly total. The trans- 

 formation of masses of population by imperceptible steps guided 

 by selection, is, as most of us now see, so inapplicable to the 

 facts, whether of variation or of specificity, that we can only 

 marvel both at the want of penetration displayed by the advo- 

 cates of such a proposition, and at the forensic skill by which it 

 was made to appear acceptable even for a time. 



In place of this doctrine we have little teaching of a positive 

 kind to offer. We have direct perception that new forms of life 

 may arise sporadically, and that they differ from their progenitors 

 quite sufficiently to pass for species. By the success and main- 

 tenance of such sporadically arising forms, moreover, there is 

 no reasonable doubt that innumerable strains, whether in isola- 



