68 PHYSICAL BASIS OF CIVILIZATION 



tending to stimulate them in the use of whatever 

 degree of intelligence they were endowed with, then 

 this slight difference in incentive to its use and the 

 urgent need of it might offer a point of departure, a 

 plane of cleavage, where the small end of the wedge 

 of natural selection might enter, and this, in practi- 

 cally infinite time, might lead to a degree of intelli- 

 gence such as is displayed by the most advanced 

 minds of our generation. 1 



For when, during a long period, measured in this 

 case probably by hundreds of thousands if not mil- 

 lions of years, destructive agencies eliminate the 

 great majority of certain creatures before they can 

 reach the reproductive age, then, as more fully ex- 

 plained earlier in these essays, natural selection is 

 able to work on a very small margin, and, still by the 

 accumulation of many of these small margins from 

 generation to generation through many ages, to 

 accomplish astonishingly cumulative results. For 



1 To account for the wonder of the survival of the two-footed 

 upright brute, it has been suggested that, in the earlier genera- 

 tions, before the expansion of intelligence and the use of sticks 

 and missiles had begun, our ancestors dwelt in some favored 

 spot where no fierce or powerful competitors or enemies existed ; 

 that there they acquired a high order of intelligence and became 

 proficient in the use of tools and weapons, and thereafter issued 

 forth to conquer the earth. This is obviously a purely arbitrary 

 guess suggested by the story of the (j-arden of Eden. Only a 

 miracle could have kept such retreats from being overrun by 

 man's competitors and enemies, or from leaving some evidence 

 of their former existence to posterity of these asylums. Further- 

 more, the unique and enormous expansion of human intelligence 

 would seem miraculous, if the helplessness of our ancestry and 

 the absence of such hypothetical safe retreats sufficiently ex- 

 tensive for the habitat of the whole race had not been the inevi- 

 table exciting cause of it. 



