CHAPTER XI. 



STERILITY OF HYBRIDS. CONCLUDING REMARKS. 



WHEN we consider the bearing of recent discoveries on those 

 comprehensive schemes of evolution with which we were formerly 

 satisfied, we find that certain details of the process are more easy 

 to imagine. We readily now understand how varieties once 

 formed, can persist, but at the same time difficulties hitherto 

 faced with complacency become formidable in the light of the 

 new knowledge. So generally is this admitted by those familiar 

 with modern genetic research that most are rightly inclined to 

 postpone the discussion. The premisses, indeed, on which such 

 a discussion must be based are almost wholly wanting. 



The difficulties to which I chiefly refer are not those created 

 by the phenomena of adaptation, though they are serious enough. 

 In treating of that subject I* have felt obliged to express scepti- 

 cism as to the validity of nearly all the new evidence for the 

 transmission of acquired characters. At the present time the 

 utmost we are bound to accept is the proof that (i) in some 

 parthenogenetic forms variations, or perhaps we may say mal- 

 formations, produced in response to special conditions, recur in 

 one or perhaps two generations asexually produced after removal 

 to other conditions. (2) That violent maltreatment may in rare 

 instances so affect the germ-cells contained in the parents as to 

 cause the individuals resulting from the fertilisation of those 

 cells to exhibit an arrest of development similar to that which 

 their parents underwent. 



I do not doubt that evidence of this type will be greatly 

 extended. As a contribution to genetic physiology these facts 

 are very important and interesting, but I cannot think that any 

 one, on reflexion, will feel encouraged by such indications to 

 revive old beliefs in the direct origin of adaptations. 



In these respects we are simply left where we were. The 

 force of objections based upon the existence of adaptative 



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