194 IOWA ACADEMY OF SCIENCES. 



ness extends to the realm of psychology, and that activities 

 ■which would unhesitatingly be ascribed to reason if exhibited 

 by man, should be regarded as evidence of reason when exhib- 

 ite 1 by organisms closely allied to man, until evidence to the 

 contrary is forthcoming. 



It is entirely unnecessary in this presence to show the very 

 great likeness in morphology and physiology between man and 

 the other mammalia. The more minute our investigations, 

 the more are we impressed with this similarity. Almost every 

 bone found in the one is found in the other. A striking illus- 

 tration of this similarity was furnished lately when a taxider- 

 mist used the skeleton of the human hand as an aid in articula- 

 ting the bones of a fore-foot of the wombat, an animal at the 

 opposite end of the mammalian series. "But,'' it may be 

 objected, "the great physical difference between man and brute 

 is in the brain." Granted. But the difference is quantitative, 

 not qualitative. So far as I know there is no kind of brain cell 

 in man that is not found in the brute. The difference in quan- 

 tity is enormous, but that in quality is yet to be discovered. 



In physiological matters the same conclusion is inevitable. 

 The various organs in animals are strictly homologous with 

 those of man in structure and also in functi' n. They act, in 

 general, in the same way in both under similar conditions. But 

 that which is rightly regarded as most conclusive of all is the 

 fact that medicines and poisons act in the same way in both. 

 When we know the effect of a certain drug in man we can con- 

 fidently predict the same effect would ensue if the dog were 

 treated with that drug. It is also true in general that the same 

 diseases affect man and the apes, for instance, in the same way. 

 Consumption might almost be said to be the natural death of 

 captured monkeys, so prevalent is it 



I maintain, then, that we have a perfect right to insist that in 

 view of these innumerable homologies, the overwhelming pre- 

 sumption is in favor of like actions being indices of like mental 

 states in both; and that when a given activity on the part of 

 an animal appears to indicate the exercise of reason, the 

 assumption is that the animal does reason, and that assumption 

 logically stands until it is swept away by conclusive evidence 

 to the contrary. 



It will be seen from what I have already said that Pr^ fessor 

 Morgan, in contemplating the apparently rational acts of 

 animals, demands that they be regarded as irrational if it is 



