294 



HABIT AND INTELLIGENCE. 



[chap. 



tissue to its function — is totally insoluble. And certainly, 

 at a first glance, the question how germinal matter has 

 acquired the power of transforming itself into cellular 

 tissue, bone, muscle, and nerve, appears at least as far 

 heyond the possibility of solution as the question why 

 oxygen and hydrogen combine into water, or nitrogen and 

 carbon into cyanogen. Nevertheless it is worth while to 

 inquire whether it is possible to suggest any physical causes 

 for these transformations : if we come to the conclusioia 

 that none such are possible to assign, even such a negative 

 conclusion will be valuable ; and if we are compelled to 

 keep our judgment in suspense, it will be well to have 

 stated the question. With respect to morphological adap- 

 tations — as, for instance, the question how, and by Avhat 

 physical process or physical cause, a limb which is homo- 

 logically identical with the pectoral fin of the fish has been 

 transformed into tlie leg of the quadruped, into the wing of 

 the pterodactyle, the bird, and the bat, and into the hand 

 of man; — with respect to this class of questions, I say, it 

 does not appear so hopeless to seek for a solution. In 

 speaking of the laws of habit and variation in a former 

 chapter, it has been explained at some length how organ- 

 isms have a very considerable power of adapting them- 

 selves to changing circumstances, necessitating a change in 

 the mode of life. The problem before us may be thus 

 stated, in words somewhat different from those employed 

 above : — Is it possible that all of the almost infinitely com- 

 plex adaptations of the organic creation can be produced 

 by any action, direct or indirect, of inorganic forces on the 

 organism, and the actions of the organism in response 

 thereto ; the effects of all such actions being, of course, 

 accumulated by hereditary habit, and complicated with 

 the laws of the correlation of variations 1 



^Vhen I speak of a direct process, I mean, of course, the 



. process of spontaneous self-adaptation to circumstances, of 



which all organisms are in some degree capable. By an 



natiiral^'^' indirect process, I mean that of " natural selection among 



spontaneous variations," according to Darwin's law. These 



two causes — self-adaptation and natural selection — are the 



The 



proLlem 



stated. 



Two pos- 

 sible 



processes 

 self-adap- 

 tation, I 

 natural 

 selection 



