262 Why Living 



muscular contraction, and increased se- 

 cretion of the tear gland. In this case 

 there are two quite different effectors. 

 Many responses to a stimulus are not 

 visible. In the case of the automobile ap- 

 proaching you the hearing of the horn 

 is itself a response; recognizing the noise 

 as a horn is another response; the feeling 

 of pain and the feeling of fright which 

 follow are also responses; and there are 

 many other possible responses. Sometimes 

 a response follows upon a stimulus im- 

 mediately; at other times it may be de- 

 layed a long time. 



Unlearned responses in all animals. In 

 you, as in all other animals, there are 

 responses that are inborn or unlearned. 

 The suckina^ movements made by a 

 baby's mouth when its lips come in con- 

 tact with any object and the clasping 

 movements made by the baby's fingers 

 when they touch your finger or a stick 

 are inborn responses made by all babies. 

 Unexpectedly touching a hot stove, pro- 

 vided the stove is hot enough, will al- 

 ways cause the hand to be jerked away. 

 This, too, is inborn and unlearned. The 

 same response is made by you and by me 

 and by a very young child. An act of 

 this kind, which is a simple direct re- 

 sponse to a stimulus and which is inborn 

 and unlearned, is called a reflex act or 

 simply a reflex. Starting at the sound of 

 a loud noise, blinking when a cinder en- 

 ters the eye, and the secreting by the 

 tear gland at this time are also reflex 

 acts. 



There are many reflexes in us and in 

 all other animals which occur internally 

 and which are therefore not noticed. 

 When food reaches the top of the food 

 pipe a ring of muscle contracts; by the 



Things Behave As They Do unit v 



contraction and relaxation of this muscle 

 the food is pushed to the stomach. Each 

 muscular contraction is a response to a 

 stimulus and is a true reflex. When the 

 food reaches the stomach another reflex 

 is started. This time the response is made 

 by gland cells, that is, gastric juice is 

 secreted. You can demonstrate some of 

 your own reflexes by doing Exercises 

 I, 2, and 3. 



How much of the animal's behavior is 

 reflex? You will learn that many animals 

 perform some acts which are not reflexes. 

 But, in general, the less complex an ani- 

 mal is, the greater is the proportion of 

 its reflex acts. In the simpler vertebrates, 

 such as the fish, amphibians, reptiles, and 

 even birds, almost all behavior is inborn 

 and unlearned (reflex). Very few acts 

 seem to be learned during the lifetime of 

 the individual. In more complex verte- 

 brates, such as mammals, there is a greater 

 proportion of learned behavior. Much of 

 man's behavior is learned, as you will 

 see. The mammals most nearly like man, 

 such as the apes, have a greater amount 

 of learned behavior than the mammals 

 that are less like man. But no other ani- 

 mals can learn nearly as much as m_an 

 can. 



As far as we know, among inverte- 

 brates behavior seems to be largely, if 

 not entirely, unlearned behavior. The 

 elaborate routine performed by spiders, 

 by ants in their nests, by bees in their 

 hives, by wasps in nest building, and by 

 beavers in making dams is unlearned. 

 Without study we might be led to be- 

 lieve that much of this behavior is learned 

 and carefully thought out. It is not. Let 

 us examine some of the behavior of sev- 

 eral animals more closely. 



