182 General Biology 



We have seen in our study of past chapters that the unicellular 

 Paramoecium has only two simple reactions, namely, a backward and 

 forward movement, while the vertebrate frog can move in many and 

 varying ways in order to get out of harm's way. Probably all animals 

 can learn. That is, they can be taught to make some change in their 

 behavior, but the rate of speed with which they can learn probably 

 becomes greater as we ascend from lower to higher phyla. The same 

 may be said of the complexity of the problems to be learned. 



When left to themselves, all animals and children learn whatever 

 they do learn by what is called the trial-and-error method. This simply 

 means that they try something and, if this something is unpleasant or 

 painful, they try something else. Contrariwise, if a reaction produces 

 pleasure, it is done again and again until it becomes a habit. 



All learning, no matter what it may be, must, however, be based 

 on instinct in its widest sense. That is, the problem presented must 

 be something which can be solved by making use of some instinctive 

 behavior of the animal upon which we wish to experiment. For example, 

 a cat can be placed in a closed box in which there is a lever, which, 

 when pressed, will open a door. Now, cats are excitable and, when 

 excited, will begin to leap about. This is an instinctive action. If, while 

 leaping about, the animal strikes the lever and the door opens, it can 

 be trained, by enclosing it often enough in the same or a similar box, to 

 press the lever without going through the leaping first. 



Learning, then, really means profiting by past experience. But no 

 profiting by past experience is possible unless such past experience is 

 remembered. Now, such memory by no means must be a definite 

 thinking out of a past event and then sitting back and saying "I will" 

 or "I will not do this again." Most physical experiences, even in man, 

 are merely non-conscious functioning of nerve-arcs. Neither men nor 

 the lower animals do any thinking in regard to these simple or complex- 

 chain-reflex actions. It is a mere association of one stimulus starting 

 another and is called, as already stated, sensory, or associative memory. 



There may, or may not, be an awareness of doing an act, plus an 

 associated pleasure or pain sensation. That is, there may be conscious- 

 ness not only of the fact that an act is being performed, but there may 

 also be an awareness of pleasure and pain, accompanying it, though 

 there is little proof that a definite thought — that is, reasoning — is per- 

 formed, and that it is then due to such reasoning that changes of action 

 are made. These learning acts are in all probability due only to sensory 

 memory. ■ 



An example comes to mind. We have all heard some one tell of 

 a horse that knows when Sunday comes, that being the only day when 

 the animal does not come out of the stable to be harnessed as soon as 

 its master appears. 



But does this show that the horse can count up to seven and has 



