viii PEEFACE. 



them would have been useless without some trustworthy 

 principles of selection. The first and most obvious principle 

 that occurred to me was to regard only those facts which 

 stood upon the authority of observers well known as com- 

 petent ; but I soon found that this principle constituted 

 much too close a mesh. Where one of my objects was to 

 determine the upper limit of intelligence reached by this 

 and that class, order, or species of animals, I usually found 

 that the most remarkable instances of the display of intel- 

 ligence were recorded by persons bearing names more or 

 less unknown to fame. This, of course, is what we might 

 antecedently expect, as it is obvious that the chances must 

 always be greatly against the more intelligent individuals 

 among animals happening to fall under the observation of 

 the more intelligent individuals among men. Therefore I 

 soon found that I had to choose between neglecting all the 

 more important part of the evidence and consequently in 

 most cases feeling sure that I had fixed the upper limit 

 of intelligence too low or supplementing the principle of 

 looking to authority alone with some other principles of 

 selection, which, while embracing the enormous class of 

 alleged facts recorded by unknown observers, might be 

 felt to meet the requirements of u reasonably critical 

 method. I therefore adopted the following principles as a 

 filter to this class of facts. First, never to accept an alleged 

 fact without the authority of some name. Second, in the 

 case of the name being unknown, and the alleged fact of 

 sufficient importance to be entertained, carefully to con- 

 sider whether, from all the circumstances of the case as 

 recorded, there was any considerable opportunity for mal- 

 observation ; this principle generally demanded that the 

 alleged fact, or action on the part of the animal, should be 

 of a particularly marked and unmistakable kind, looking 

 to the end which the action is said to have accomplished. 



