ii2 THE EVOLUTION OF MAN 



and thinking. This amounts to saying that there is in the 

 animal kingdom, as we know it, the widest range of behavior 

 extending from that which at one end of the line is almost, if 

 not wholly, stereotyped and mechanical to forms which at the 

 other extreme represent not only a rich life of plastic instinct, 

 but also highly variable forms of behavior, some of which 

 definitely suggest the possession of rudimentary intelligent 

 powers. There is, then, conclusive evidence of a real evolu- 

 tionary process, if one assume, as all scientists now do, that 

 the more complex organisms, in which behavior is most 

 elaborate and intelligent, have arisen from simpler and his- 

 torically antecedent forms. That is to say, there is no question 

 whatever regarding the wide variety of the present modes of 

 behavior extending from the reflex and tropistic type up to 

 the variable intelligent type, and, on the basis of the evolution- 

 ary conception of organic structures, there can be no question 

 that these differences in behavior represent historic evolution 

 of the more complex out of the simpler. 



INTELLIGENCE AND CONSCIOUSNESS 



This is perhaps a convenient point at which to mention an 

 issue often much magnified in discussions of mental evolution, 

 to wit: Are all animals conscious, or is consciousness a phe- 

 nomenon which appears only at a certain stage of evolutionary 

 development? 



Disregarding earlier historic theories, there have been 

 three distinct positions represented by contemporary scientific 

 opinion. One of these holds that all animals are conscious, 

 even an amoeba. Indeed, the defenders of this extreme view 

 have sometimes gone further in maintaining not only that all 

 life, plant as well as animal, enjoys at least a rudimentary form 

 of consciousness, but also that the whole physical universe is 

 but one aspect of a reality, which seen in its entirety presents 



