38 Through the Brazilian Wilderness 



another set of cases, in the development and preservation 

 of species. Courage, intelligence, adaptability, prowess, 

 bodily vigor, speed, alertness, ability to hide, ability to 

 build structures which will protect the young while they 

 are helpless, fecundity — all, and many more like them, 

 have their several places; and 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 survival 

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

 vival value whatever, and in yet others, although of 

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

 conferred on foes or rivals by totally different attri- 

 butes. Intelligence, for instance, is of course a survival 

 factor ; but to-day there exist multitudes of animals with 

 very little intelligence which have persisted through im- 

 mense periods of geologic time either unchanged or else 

 without any change in the direction of increased intelli- 

 gence; and during their species-life they have witnessed 

 the death of countless other species of far greater in- 

 telligence 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 de- 

 velopment, 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 convenient but far from satisfactory term as 

 orthogenesis. 



