THE START 37 



behind all these visible causes there are at work other and 

 often more potent causes of which as yet science can say 

 nothing. Some species owe much to a given attribute 

 which may be wholly lacking in influence on other species; 

 and every one of the attributes above enumerated is a sur- 

 vival factor in some species, while in others it has no sur- 

 vival value whatever, and in yet others, although of bene- 

 fit, it is not of sufficient benefit to offset the benefit conferred 

 on foes or rivals by totally different attributes. Intelli- 

 gence, for instance, is of course a survival factor; but 

 to-day there exist multitudes of animals with very little 

 intelligence which have persisted through immense periods 

 of geologic time either unchanged or else without any 

 change in the direction of increased intelligence; and dur- 

 ing their species-life they have witnessed the death of 

 countless other species of far greater intelligence but in 

 other ways less adapted to succeed in the environmental 

 complex. The same statement can be made of all the 

 many, many other known factors in development, from 

 fecundity to concealing coloration; and behind them lie 

 forces as to which we veil our ignorance by the use of 

 high-sounding nomenclature — as when we use such a con- 

 venient but far from satisfactory term as orthogenesis. 



