A Suggestion on Extinction. 479 



cerned in the amphymyxis, or the more rigid the selection 

 of forms that varied in the same direction, the greater would 

 be the limit set on the resulting potential variation, and the 

 more rapid would be the resulting actual variation. I may 

 say that this result is apparently what does occur, not only 

 as we proceed from lower to higher forms of life, but also as 

 the result of true breeding by careful selection of variations 

 of the type. It is also seen that if in-breeding on a close 

 scale should occur, the potential variation that is brought 

 about by the union may be so lessened that it becomes 

 almost a matter of self-fertilisation, with possibilities of 

 pathological results. 



Let us next turn to see what effect Natural Selection 

 would have in regard to these matters. It has been fully 

 demonstrated by Darwin that specialisation is the result of 

 Natural Selection. He pointed out that species are formed 

 from species by a selection of certain variations of the parent 

 species, and that by a process of what might be termed true 

 breeding of these variations, and usually to the detriment of 

 less successful types, in time such a divergence took place 

 between the different selected variations that they ceased to 

 congregate with each other, and often to be even fertile the 

 one with the other, and that in this way new species came 

 into existence. These new species would have their period 

 of dominance, and produce new variations, upon which in 

 turn Natural Selection would come into play, and again 

 choose a few forms to start a new stock. In those forms 

 which varied rapidly. Natural Selection would be most rigid, 

 while in forms like Lingula and Nautilus, which tended to 

 vary but little, the hand of death would be much more 

 indiscriminate. 



If we apply what has been said before regarding 

 potential variation, we see that as Natural Selection is 

 more rigid, the greater is the limit set upon the poten- 

 tial variation, and, moreover, that the individuals of the 

 groups, however numerous they may have become during 

 their period of dominance, are becoming more and more 

 alike as regards the restriction of their potential variation. 

 Natural Selection of a rigid kind would therefore tend to 



