560 Causes and Course of Organic Evolution 



ing an exemplification of the truth that zoological or structural 

 affinity is only related in a most loose and general way to psy- 

 chological or mental similarity. Up to a certain point, how- 

 ever, even here we meet with an exemplification of what I may 

 call a complementary truth, namely, that similarity of organiza- 

 tion and environment is in a general way related to similarity 

 of instincts (though not necessarily of intelligence). This is 

 obviously the case with the habit from which the order takes 

 its name ; for, whether the instinct of gnawing is here the cause 

 or the result of peculiar organization, the instinct is unques- 

 tionably correlated with the peculiarity. And similarly, though 

 less obviously, is this the case with the instinct of storing food 

 for winter consumption which is more prevalent among the 

 rodents than in any other order of mammals — rats, mice, 

 squirrels, harvesters, beavers, etc., all manifesting it with re- 

 markable vigor and persistency. Here we probably have a case 

 of similar organization and environment determining the same 

 instinct; for the latter is not of sufficiently general occurrence 

 among all species of rodents to allow us to suppose that the 

 species in which it does occur have derived it from a common 

 ancestry." 



As will be explained later, we would attribute practically all 

 of the above "instinct" and "intelligence" to environal ac- 

 tion and proenvironal response. This starts, by long continued 

 repetition, definite stereoenergetic currents, along certain tiss- 

 ues, that effect a stereo-chemical placing of definite mole- 

 cules. There thus arises an acquired and inherited act, through 

 lines of energy flow proceeding more readily along one pathway 

 than another, and so determining the nervous, the muscular, the 

 osseous, and other modifications that have generally taken place. 



But we would take exception to the first clause of the above 

 quotation from Romanes: "In no other group of animals," etc. 

 For between a Nautilus and a Loligo, between a hemipterid 

 and an ant, between an Apteryx and a parrot, the cogitic dif- 

 ferences are at least as great, we should incline to say much 

 greater, than between the least and the most advanced rodent 

 mentally. 



