50 FIFTY YEARS OF DARWINISM 



depends on the perfection of its adaptation to its sur- 

 rounding conditions." 



After maintaining that the stability of states 

 rises and declines, culminating when it reaches 

 zero in revolution or extinction, and that the 

 physicist witnesses results analogous with those 

 studied by the politician and the historian, the 

 author continues: — 



" These considerations lead me to express a doubt 

 whether the biologists have been correct in looking for 

 continuous transformation of species. Judging by 

 analogy we should rather expect to find slight con- 

 tinuous changes occurring during a long period of 

 time, followed by a somewhat sudden transformation 

 into a new species, or by rapid extinction." ^ 



I do not, of course, doubt that there is reality 

 in the analogy between the evolution of states 

 and of species, but it is not, I submit, close 

 enough to justify the author's reasoning from 

 one to the other. The communities of the social 

 Hymenoptera present much closer analogies with 

 political states, and yet even here it would be 

 unjustifiable to infer that the evolution of insect 

 societies has been discontinuous. 



' The following footnote is appended to Sir George Darwin's 

 address: — "If we may illustrate this graphically, I suggest that 

 the process of transformation may be represented by long lines 

 of gentle slope, followed by shorter lines of steeper slope. The 

 alternative is a continuous uniform slope of change. If the 

 former view is correct, it would explain why it should not be 

 easy to detect specific change in actual operation. Some of my 

 critics have erroneously thought that I advocate specific change 

 per saltwm,." 



In reply to this note it may be pointed out that " per saltum 

 evolution " or " discontinuous evolution " differs from " continu- 

 ous evolution " only in the steepness of the slope of change. 



