46 Heredity and Environment 



tively simple beginnings. All children come gradually to an age of 

 intelligence and reason. In its simpler forms at least reason may 

 be defined as the power of predicting future events and of reaching 

 conclusions regarding unexperienced phenomena under the influ- 

 ence of past experience. In the absence of individual experience 

 young children have none of this power, but it comes gradually 

 as a result of remembering past experiences and of' fitting such 

 experiences into new conditions. 



Useful Responses. — Young infants and many lower animals 

 lack the power of reason, though their behavior is frequently of 

 such a sort as to suggest that they are reasoning. Even the low- 

 est animals avoid injurious substances and conditions and find 

 beneficial ones; more complex animals learn to move objects, solve 

 problems, and find their way through labyrinths in the shortest 

 and most economical way ; but this apparently intelligent and pur- 

 posive behavior has been shown to be due to the gradual elimina- 

 tion of all sorts of useless activities, and to the persistence of the 

 useful ones. 



The ciliated infusorian, Paramecium, moves by the beating of 

 cilia, which are arranged in such a way that they drive the ani- 

 mal forward in a spiral course. However, when it is strongly ir- 

 ritated, the normal forward movement is reversed ; the cilia beat 

 forward instead of backward and the animal is driven backward 

 for some distance (Fig. 21, 1, 2, 3) ; it then stands nearly still, 

 merely rolling over and swerving toward the aboral side, and 

 finally it goes ahead again, usually on a new course (Fig. 21, 

 3, 4, 5, 6). These movements seem to be conditioned rather 

 rigidly by the organization of the animal : they, are more or less 

 fixed and mechanical in character, though to a certain extent 

 they may be modified by experience or physiological states. Para- 

 mecium behaves as it does in virtue of its constitution, just as an 

 egg develops in a particular way because of its particular organi- 

 zation. 



"Trial and Error." — But although limited in its behavior to 



