XVII 



THE DISPLAY OF ENERGY 



Preview. Why living things are responsive • Various kinds of stimuH • 

 Tropisms • Nature of responses • Mechanism of response in plants • Mech- 

 anisms of response in animals • Tropisms, reflexes, and native behaviors • 

 Native behaviors may be modified • Habit formation • Conditioned behav- 

 iors • Are behaviors adaptive responses? • When are animals conscious? • 

 Emotional responses • What is intelligence? • Intelligence of apes • Intelli- 

 gence of man • The measurement of intelligence • Suggested readings. 



PREVIEW 



The display of energy is characteristic of all living things. We 

 may predict quite accurately what forms energy will take in very 

 simple plants and animals, since they react variously but consistently 

 to factors of the environment, such as light, temperature, and mois- 

 ture, by making definite turning movements, growth movements, or 

 by other behavior. These expressions of behavior are called tropisms. 



When it comes to answering the question, "Why do we behave 

 like human beings?" we are faced with a much more difficult problem, 

 for the more complex the organism, the more complicated are its 

 behavior patterns. 



Comparing the behavior of plants with that of animals and using 

 the same stimuli in each case, we find in general that, correlated with 

 the lack of muscles and a nervous system, in plants responses to 

 stimuli are slow and usually expressed as growth movements. In 

 animals which, except in the lowest forms, have both muscles and a 

 nervous apparatus, the reaction to a given stimulus is a response in 

 the form of some sort of motion such as swimming, flying, crawling, 

 walking, or running. 



Two very definite theories of animal behavior are held. One 

 theory recognizes animals as living machines, giving definite and 

 unchangeable responses to certain stimuli. In such a mechanistic 

 view of life the organism is considered in terms of groups of cells and 

 tissues, or of the elements of which it is composed. When the ma- 

 chine is very complex its actions are less predictable because the 

 same stimulus may cause a different reaction to a different part of 

 the machine. Light, for example, would evoke a response only from 



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