220 COOK 



The selection which would eliminate the over-wise insects 

 would not be applied to them directly, but to the trees which 

 have become completely dependent upon their insect servants. 

 Their highly specialized flower-receptacles are so tightly closed 

 that no other insects will enter. 1 When once such a delicate 

 adjustment of structures and instincts breaks down, the parts are 

 as useless as a watch that will not keep time. The utility de- 

 pends only on the adjustment, and when the adjustment has 

 become highly complex changes are far more likely to disturb 

 than to improve it. Highly specialized types, those upon which 

 selection has exerted the most successful influence, are ever the 

 most liable to sudden and complete extinction, as geological 

 history has already shown. 



Close adjustments induced by selective influence are not, in 

 the long run, truly advantageous. The chances of survival are 

 not increased by close adjustment, but by the continuation of 

 development of characters which allow a wide range of possi- 

 bilities of existence under different environmental conditions. 

 From the standpoint of the species, changes of the environment 

 are fortuitous, and the utility of adjustments is also fortuitous 

 and temporary. Indeed, the study of adaptations alone might 

 have suggested caution in the acceptance of the doctrine of en- 

 vironmental causation, for a vast number of adaptations, and 

 perhaps the majority of them, do not have reference to the en- 

 vironment, but are devices for keeping the species together, that 

 is, for facilitating symbasic interbreeding. To this class of sym- 

 basic adaptations belong the whole series of specializations of 

 flowers to secure the visits of insects, the group of phenomena 

 which has probably figured more largely than any other as an 

 evidence that adaptation is a genuine phenomenon of nature and 

 not merely an elaborate collection of coincidences. These 

 cross-fertilizing adaptations are real and wonderful, but the 

 plants instead of having been acted upon by external influences 

 have taken advantage of the environment to enable them to 



1 A wild species of fig native in the Comitan district of the Mexican state of 

 Chiapas has its fruits so completely closed that even the fig insects can no longer 

 emerge by the natural aperture, but are obliged to bore through the wall of the 

 fruit to let themselves out. Mr. W. T. Swingle informs me that this is true also 

 of the sycamore-figs of the Old World. 



