104 THE EVOLUTION OF MAN 



evidence of change and development, of rise and fall, in the 

 tide of animal life, in its geographical range, in its anatomical 

 organization, and in its adjustability to the major features of 

 environment. One of the lectures in this series has in particu- 

 lar been devoted to evidence of this character as it applies to 

 the changes brought about in the nervous system of various 

 forms of animal life. The development of man himself and of 

 the society within which he lives has also been passed in review 

 and convincing demonstration has been offered of the extensive 

 changes which have, throughout the ages, come to pass in both. 

 Evolution having been thus convincingly exhibited in a number 

 of important fields, it behooves us, in discussing the present 

 problem, to secure impressions as clear as possible of the char- 

 acter of the evidence upon which we are to base our inferences 

 and conclusions regarding the development of intelligence. 



ANIMAL INTELLIGENCE 



In the case of animal life, the only available information is 

 to be gained by the direct observation of animal behavior as 

 that is found among the creatures surviving in our age of the 

 world. Whether there may have been creatures in the past 

 possessing forms of intelligence substantially different from 

 that of any animals now living can neither be denied nor as- 

 serted with absolute confidence. But such evidence as we have 

 is at least all against the inference that animals superior to 

 those now living have ever been developed. So great is the 

 similarity of existing forms to such extinct forms as are known 

 to us, that it seems highly improbable there should have oc- 

 curred developments of intelligence widely different from those 

 represented in the animal life of to-day. This inference, 

 to be sure, rests upon the hypothesis which most scientists re- 

 gard as conclusively established, to wit, that intelligence is 



