156 MENTAL EVOLUTION IN MAN. 



Sprang from some other species of man-like creature, and 

 became human in virtue of the power of articulation plus all 

 the other conditions external and internal, therefore the 

 talking birds ought to have developed some similar progeny, 

 merely because they happen to satisfy one of these conditions. 



Take a fair analogy. Flying is no doubt a very useful 

 faculty to all animals which present it, and it is shown to 

 be mechanically possible in animals so unlike one another as 

 Insects, Reptiles, Birds, and Mammals. We might therefore 

 suppose that, from the fact of bats being able to fly, many 

 other mammals should have acquired the art. But, as they have 

 not done so, we can only say that the reason is because the 

 complex conditions leading to the growth of this faculty have 

 been satisfied in the bats alone. Similarly " the flight of 

 thought " is a most useful faculty, and it has only been 

 developed in man. One of the conditions required for its 

 development — power of articulation — occurs also in a few birds. 

 But to argue from this that these birds ought to have developed 

 the faculty of thought, would be just as unwarrantable as to 

 argue that some other mammals ought to have developed the 

 faculty of flight, seeing that they all present the most important 

 of the needful conditions — to wit, bones and muscles actuated 

 by nerves. Indeed, the argument would be even more un- 

 warranted than this ; for we can see plainly enough that the 

 most important conditions required for the development of 

 thought are of a psychological and social kind — those which 

 are merely anatomical being but of secondary value, even 

 though, as I have endeavoured to indicate, they are none the 

 less indispensable. 



In short, I am not endeavouring to argue that the influence 

 of articulation on the development of thought is in any way 

 magical. Therefore, the mere fact that certain birds are able 

 to make articulate sounds in itself furnishes no more difficulty 

 to my argument than the fact that they are able to imitate a 

 variety of other sounds. For the psychological use of articulate 

 sounds can only be developed in the presence of many other 

 and highly complex conditions, few if any of which can be 



