468 - Multicellular Animals, Especially Man 



responses just as well initially as subse- 

 quently. The infant starts breathing; it sucks 

 upon the breast; it salivates when anything 

 is placed in the mouth; and so forth. In fact, 

 even before birth, while the fetus is in utero, 

 many visceral responses, such as the heart- 

 beat and the peristaltic movements of the 

 gastrointestinal tract — and some somatic re- 

 sponses, such as movements of the arms and 

 legs — begin to lake place at appropriate 

 stages in development. 



Unconditioned Reflexes. Regardless of 

 complexity, any standardized response to a 

 standardized stimulation, which can be exe- 

 cuted by an organism without benefit of pre- 

 vious experience, is called an unconditioned 

 reflex. In higher animals such responses in- 

 dicate the existence of a number oi highly 

 conductive reflex arcs, in which the synapses 

 offer virtually no resistance to impulses, even 

 in the absence of the facilitating effects of 

 previous transmission. 



Depending on complexity, unconditioned 

 reflexes are classified as (1) simple uncondi- 

 tioned reflexes, which involve only a few 

 quite localized receptors and effectors; and 

 (2) compound unconditioned reflexes — for- 

 merly known as instincts — which involve 

 many receptors and effectors, acting in se- 

 quence. Essentially, it is thought, compound 

 reflexes represent a train of interlocking 

 simple reflexes, each touched off by its prede- 

 cessor. However, the line of distinction be- 

 tween simple and compound reflexes is quite 

 arbitrary. In man, for example, coughing, 

 salivating, and swallowing are usually classi- 

 fied as simple reflexes, whereas sucking, chew- 

 ing, and spitting out disagreeable material 

 are regarded as compound reflexes. 



A conspicuous feature of unconditioned 

 reflexes is their survival value to the organ- 

 ism. In most cases, they serve in one way or 

 another to secure the welfare of the indi- 

 vidual and to foster the perpetuation of the 

 species. This characteristic, however, does 

 not imply any consciousness on the part of 

 the animal as to the consequences of its acts. 

 It merely means that different organisms have 



developed a structural and functional capac- 

 ity to execute certain self-preserving re- 

 sponses, anil these organisms continue to 

 survive and perpetuate themselves, each ac- 

 cording to its kind. 



The lack of any "conscious purpose" in 

 unconditioned reflexes is clearly shown by 

 the fact that their "usefulness" applies only 

 under the natural conditions of the animal's 

 age-old habitat. When some feature of the 

 natural environment is changed, the animal 

 still responds in the same old way to the 

 same old stimulus, even though the response 

 may now be useless, or even injurious. Moths, 

 for example, always fly toward the light. 

 Under primeval conditions this was un- 

 doubtedly a useful response, since the moth 

 is a nocturnal flyer ami depends upon white 

 or fight-colored flowers as a source of nectar. 

 But with the introduction of fires and lamps 

 into the moth's environment, this response 

 became virtually suicidal — but nevertheless 

 it persists. The moth Hies into the flame for 

 the same reason that it flies to a white flower 

 — not because it knows the flower to be nutri- 

 tious, nor because it thinks the flame to be 

 a flower — but because its eves, nervous sys- 

 tem, and wing muscles are so connected that 

 an unequal illumination of the two eves sets 

 up reactions that automatically turn it to- 

 ward the light. Likewise, a majority of the 

 complex and seemingly purposeful actions of 

 lower vertebrates — such as fish, amphibians 

 and reptiles — are machinelike and unvarying 

 in nature. And even in the birds and mam- 

 mals, many of the reactions most essential to 

 survival are purely unconditioned, that is, 

 quite independent of experience and learn- 

 ing. 



Modifiability of Behavior: Conditioned 

 Reflexes. In higher animals especially, the 

 same stimulus does not invariably elicit the 

 same response, and there are a number ot 

 factors that may, to a greater or lesser extent, 

 modify the outcome of a given stimulation. 

 Combinations of two or more stimuli, applied 

 simultaneously or in close succession, often 

 change the response that would be evoked by 



