314 



SCIENCE 



[N. S. Vol. XXVI. No. 662 



phenomena of behavior of that variant of the 

 Darwinian doctrine known by the name of 

 organic selection. It is a view that lends 

 itself with especial facility to the interpreta- 

 tion of physiological evolution. It distin- 

 guishes between adaptations that are relatively 

 unstable, resulting from the capacity of given 

 individuals to accommodate themselves to 

 changing conditions, and adaptations that are 

 relatively stable, such as the inherited adapta- 

 tions characteristic of races. Its chief contri- 

 bution to the present discussion lies in the 

 recognition that acquired characters, such as 

 habits, cultivated aptitudes., advantages ob- 

 tained over competitors by larger experience, 

 may be approved by natural selection, even 

 though heredity decline to place them on a 

 permanent footing. Fortunate individual 

 adaptations of the unstable variety come then 

 to play important roles in the preservation of 

 the species, and in one sense actually deter- 

 mine the course of its evolution. Such, at 

 least, is the claim of the organic selectionists 

 with whom Jenings allies himself, and I have 

 no wish to deny the hypothesis. 



How the organism comes into accord with 

 its environment to the extent that it is able 

 to persist is determined, according to Jen- 

 nings, primarily by application of the method 

 of trial. The individual itself selects those 

 reactions which are favorable for its existence 

 from a number of random or trial reactions. 

 Let us consider a typical case. Whenever the 

 protozoon Paramecium, swimming along its 

 narrowly spiral path by means of the vibratile 

 hair-like cilia that clothe its body, chances to 

 come in contact with an impediment, whether 

 it be in the shape of a sand grain, a droplet of 

 some chemical solution or a sudden change in 

 temperature, the beat of its cilia may be re- 

 versed and it may back off for a distance vary- 

 ing with the strength of the stimulation. 

 Another reversal of the cilia then sends it 

 forward again, but not quite in the direction it 

 had previously taken. Owing to the peculiar 

 beating of its cilia, its progress is along a 

 spiral path, with the primitive gullet (hence 

 a structurally defined side) always towards 

 the axis of the spiral. On resuming a forward 



movement, the creature swerves toward the 

 side away from the mouth. This has been de- 

 scribed as an avoiding reaction, since it pro- 

 vides a method of passing obstacles. The 

 method is said to be a method of trial. Para- 

 mecium backs and fills until it chances to hit 

 upon an unobstructed pathway. ISTo cause of 

 a reversing reaction being offered, it keeps on 

 its way. Its final appropriate reaction is 

 said to be selected from a number of inap- 

 propriate trials or errors. 



How far the facts obtained from an analysis 

 of the behavior of Paramecium are applicable 

 to the analysis of behavior in general may best 

 be considered after an examination of Jen- 

 nings's scheme according to which behavior 

 develops, that is, becomes more effective: 



The behavior of any organism may become more 

 eflfeetive through an. increased tendency for the 

 first ^¥eak effects of injurious or beneficial agents 

 to cause the appropriate reaction; in other words, 

 through increased delicacy of perception and dis- 

 crimination on the part of the organism. Such a 

 change would be brought about through the law 

 of the readier resolution of physiological states 

 after repetition. When the organism is subjected 

 to a slight stimulus, this changes its physiological 

 state, though perhaps not sufficiently to cause a 

 reaction. Such a slight stimulus would be pro- 

 duced by a very weak solution of a chemical, or 

 by a slight increase in temperature. Now, sup- 

 pose that this weak stimulus, causing no reaction, 

 is regularly followed by a stronger one, as would 

 be the case if the weak chemical or slight warmth 

 were the outer boundary of a strong chemical solu- 

 tion, or of a region of high temperature toward 

 which the organism is moving. This stronger 

 stimulus would produce an intense physiological 

 state, corresponding to a marked negative reaction. 

 That is, the first (weak) physiological state is 

 regularly resolved by the action of the stimulating 

 agent into the second (intense) one, inducing reac- 

 tion. In time, the first state would come to resolve 

 itself into the second one even before the intense 

 stimulus had come into action. As a result, the 

 organism would react now to the weak stimulus, 

 as it had before reacted to the strong one. It 

 would thus be prevented from entering the region 

 of the chemical or the heat, even before any in- 

 jury had arisen. 



2. In the same way the organism may come to 

 react positively or negatively to a stimulus that is 



