Organic Selection 429 



tions (V) occur, some of which are in the direction of increased 

 adaptation (+), others in the direction of decreased adaptation (— ). 

 (2) Acquired modifications (M) also occur. Some of these are in the 

 direction of increased accommodation to circumstances (+), while 

 others are in the direction of diminished accommodation (— ). Four 

 major combinations are 



(a) +Vwith+M, 

 (6) +Vwith-M, 



(c) -Vwith+M, 

 {d) -Vwith-M. 



Of these {d) must inevitably be eliminated while (a) are selected. 

 The predominant survival of {a) entails the survival of the adaptive 

 variations which are inherited. The contributory acquisitions (+ M) 

 are not inherited ; but they are none the less factors in determining- 

 the survival of the coincident variations. It is surely abundantly 

 clear that this is Darwinism and has no tincture of Lamarck's essential 

 principle, the inheritance of acquired characters. 



Whether Darwin liiniself would have accepted this interpretation 

 of some at least of the evidence put forward by Lamarckians is 

 unfortunately a matter of conjecture. The fact remains that in his 

 interpretation of instinct and in allied questions he accepted the 

 inheritance of individually acquired modifications of behaviour and 

 structure. 



Darwin was chiefly concerned with instinct from the biological 

 rather than from the psychological point of view. Indeed it must be 

 confessed that, from the latter standpoint, his conception of instinct 

 as a " mental faculty " which '' impels " an animal to the performance 

 of certain actions, scarcely affords a satisfactory basis for genetic 

 treatment. To carry out the spirit of Darwin's teaching it is neces- 

 sary to link more closely biological and psychological evolution. The 

 first step towards this is to interpret the phenomena of instinctive 

 behaviour in terms of stimulation and response. It may be well to 

 take a particular case. Swimming on the part of a duckling is, from 

 the biological point of view, a typical example of instinctive be- 

 haviour. Gently lower a recently hatched bird into water: coordinated 

 movements of the limbs follow in rhythmical sequence. The behaviour 

 is new to the individual though it is no doubt closely related to that 

 of walking, which is no less instinctive. There is a group of stimuli 

 afforded by the "presentation" which results from partial innnersion: 

 upon this there follows as a complex response an application of 

 the functional activities in swimming ; the sequence of adaptive 

 application on the appropriate presentation is determined by racial 

 preparation. We know, it is true, but little of the physiological 

 details of what takes place in the central nervous system; but in 

 broad outline the nature of the organic mechanism and the manner 



