Mat 1, 1908] 



SCIENCE 



707 



a differential movement," or that I deny the 

 " possibility of syrmTietrical stimulation for 

 an oriented organism," depend simply on the 

 definition of stimulus and reaction as correla- 

 tive terms of purely experimental meaning. 

 I certainly believe that many animals, after 

 they have " fixed " a source of light and are 

 swimming toward it, are in a difiereut physi- 

 ological state from before. If we define 

 Btimulation somewhat indefinitely as meaning 

 any such changed physiological state, then we 

 may of course hold that they are then stimu- 

 lated. There seems to be no real difierence of 

 opinion on this matter; but the method of 

 formulation of course depends on the defini- 

 tion of the terms employed. 



A further point discussed by Torrey has to 

 do with the relation between selection and 

 adaptation. As an aid to understanding the 

 existence of adaptations in behavior, I ac- 

 cepted certain forms of the selection theory. 

 Torrey emphasizes the existence of unadap- 

 tive reactions, like that to the electric cur- 

 rent; he points out that there is no ground 

 for supposing that selection has played a part 

 in their production. To this I agree fully. 

 But since Torrey draws therefrom the con- 

 elusion that " the hypothesis advanced by 

 Jennings is not sufficiently broad to encom- 

 pass all the phenomena it is devised to ex- 

 plain," it needs to be pointed out that my 

 view was not " devised to explain " such phe- 

 nomena. A theory of selection, while directed 

 primarily to the explanation of adaptiveness, 

 requires the existence of raw material from 

 which selection may occur, and this raw ma- 

 terial must of course be largely unadaptive, 

 or there would be no ground for selection. 

 Selection can never account for the existence 

 of that from which selection is made. This, 

 I believe, was made plain in my book. " It is 

 clear that natural selection can not account 

 for the origin of anything; only that can' be 

 selected which already exists " (p. 326) . I 

 stated explicitly that the hypothesis set forth 

 was a theory of regulation; my exposition of 

 the matter opens on page 315 as follows: 

 " The question in which we are interested is 

 then the following: How can behavior de- 

 velop ? That is, how can it change so as to 



become more effective — more regulatory ? " 

 The existence of unadaptive reactions not 

 coming under this theory was recognized. 

 " The organism is composed of matter that is 

 subject to the usual laws of physics and 

 chemistry. External agents may of course 

 act on this matter directly, causing changes 

 in movement that are not regulatory " (paga 

 345). The origin of these unadaptive reac- 

 tions I did not discuss, because I had no light 

 to throw on the matter. But I emphasized 

 my conviction that the study of the laws of 

 matter and energy furnish the main field for 

 investigation, as compared with questions of 

 selection. " Whatever the part assigned to 

 natural selection, the superlative importance 

 of these laws remains ; they must continue the 

 chief field for scientific investigation " (p. 

 326). I might have said "the only field," 

 since of course the study of selection is merely 

 the study of how these laws work under cer- 

 tain complicated conditions. 



Torrey evidently overlooked my explicit 

 statements of the object and limitations of 

 the theory in question. 



This discussion of theories of development 

 tends to give the impression that these form 

 the important part of my treatment of be- 

 havior. It is, therefore, only just to point out 

 that this matter was a side issue from the 

 main purpose of my work, and was explicitly 

 put forward merely as a suggestion as to 

 what may have occurred. The short chapter 

 on this subject begins as follows : " It is not 

 the primary purpose of the present work to 

 treat the problems of development, but rather 

 to give an analysis of behavior as we now 

 find it. But the results of this analysis fur- 

 nish a certain amount of evidence as to how 

 development may have occurred; this it will 

 be well to set forth briefly." The book is 

 primarily a treatment of behavior as a branch 

 of experimental physiology. 



But I believe it to be short-sighted and un- 

 fortunate for a physiologist to attempt to set 

 in opposition physiological interpretation, on 

 the one hand, with so-called "historical" in- 

 terpretation, dealing with selection and evolu- 

 tion, on the other. Selection is not something 

 outside of physiological or physico-chemical ■ 



