Conclusions , 327 



tions bettered the instruction of their parents until the 

 fifth generation could learn to run for food on hearing the 

 bell after only five trials! Particulars were promised, but 

 so far have not been forthcoming. Serious doubt is cast 

 upon this report not only by those whose experience is with 

 the biology of white rats, but also by those whose experience 

 is with the learning processes in animals or with the genetics 

 of mammals. For the present, the most that can be said 

 about the prematurely announced results of the Pavlov ex- 

 periment is that they are of tremendous importance — if 



true.^ 



Conclusions 



While the doctrine of transmission of the effects of 

 use and disuse, or of the effects of response to environment, 

 remains unproven it does not follow that it is impossible. 

 With all the facts of genetics and reproduction consistently 

 against this view, it may nevertheless contain a trace of truth, 

 at least in some modified form. Indeed, the relatively few 

 biologists who are inclined to favor the view are not La- 

 marckians, but Neo-Lamarckians, rejecting some of the 

 crudities of the earlier formulations, and basing their ex- 

 pectations on the fact that germ plasm must be, like other 

 protoplasm, plastic and subject to change by suitable forces. 



For the present the status of the discussion may be sum- 

 marized as follows: 



1. Living things respond to environmental changes and 

 stimuli; and some of the results of such responses are 

 adaptive. 



2. The characters or functions present in a developed 



1 In an informal statement made at the time of the Thirteenth International 

 Physiological Congress, Boston, August 1929, Pavlov explained that in checking up these 

 experiments it was found that the apparent improvement in the ability to learn, on the 

 part of successive generations of mice, was really due to an improvement in the ability 

 to teach, on the part of the experimenter! And so this "proof" of the transmission of 

 modifications drops out of the picture, at least for the present. 



