April 7, 1903.] 



SCIENCE. 



539 



descriptions. One great desideratum in 

 ethology at the present time is a satisfac- 

 tory and sufficiently elastic working classi- 

 fication of the instincts and reactions, like 

 that of the organs and organ systems of 

 the morphologist. Such a classification 

 can be developed only by comprehensive, 

 comparative study of behavior in a number 

 of genera and families and not by any 

 amount of intensive study of a few reac- 

 tions in a few species.* 



It seemed necessary to discuss ethological 

 characters at some length for the purpose 

 of vindicating their importance. Having 

 attempted this, I may say that these char- 

 acters seem to me to offer even fewer diffi- 

 culties than the morphological characters 

 to the acceptance of the mutation theory, 

 for the reason that the ethological and psy- 

 chological processes are conceived primarily 

 as qualities and not as quantities. Thus 

 the psychical elements, i. e., the simple feel- 

 ings, cravings and sensations, are disparate 

 qualitative processes which can not be de- 

 rived from one another or from some more 

 undifferentiated process. This is still more 

 evident in the case of the complex psy- 

 chical phenomena. Similarly, instincts, 

 with which ethology is most concerned, 

 when resolved into their simplest com- 

 ponents are seen to consist of discrete reac- 

 tions which can not be shown to arise from 

 one another. Although, on the other hand, 

 the measurable intensities and durations of 

 the reactions are analogous to the fluctu- 

 ating structural variations, it is even more 

 difficult for the psychologist to conceive of 

 a particular feeling, craving or sensation 

 as arising from the greater or less intensity 

 or duration of some other psychic process, 



* An avowedly provisional but elaborate ' Sys- 

 tem der tliierisehen Triebe ' was suggested several 

 years ago by U. H. Schneider in an interesting 

 work ( ' Der thierisehe Wille,' Leipzig, Ambr. Abel, 

 1880), but subsequent workers have not even 

 adopted, to say nothing of having perfected, the 

 schema. 



than it is for the morphologist to conceive 

 of the origin of new characters from the 

 fluctuating variations of structure. 



It is, of course, extremely difficult to 

 determine the first inception of an instinct 

 process, as one may point to the mutational 

 inception of a structural character. An 

 instinct is not an isolated manifestation, 

 but is always more or less influenced by or 

 inextricably bound up with other instincts. 

 Nor do we know of any instinct which 

 manifests itself only in a single species. 

 Still there are numerous cases in which we 

 seem to see more or less clearly the phylo- 

 genetic change from one instinct to an- 

 other. Take, for example, the change from 

 a flesh-eating or insectivorous to a granivo- 

 rous or vegetarian instinct, a change which 

 has undoubtedly taken place many times in 

 the animal kingdom and is still taking 

 place, especially among insects, birds and 

 mammals. The organs which are useful 

 in obtaining, comminuting and digesting 

 animal food will function with a certain 

 degree of efficiency when vegetable food is 

 substituted, and the animal can pass either 

 at once from animal to vegetable food or 

 through a stage in which both kinds of food 

 are eaten. In the latter case, only after 

 the transition has been completed can we 

 suppose that the organs will begin to as- 

 sume the more perfect structural adapta- 

 tions to a vegetarian diet. The state in 

 which the animal is both carnivorous and 

 vegetarian may be regarded as one in which 

 two instincts coexist, and the purely vege- 

 tarian is reached by the mixtational acquisi- 

 tion of a new and the mutational loss of an 

 old instinct. Undoubtedly many changes 

 of instinct are brought about in this man- 

 ner so analogous to what has been called 

 in morphology the ' substitution of organs. ' 



Mutation is even more urgently demand- 

 ed for the explanation of many other in- 

 stincts, especially those of symbiotic and 

 parasitic species and of species with pro- 



