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) +V with +M, (c) —V with + M, 
(6) +V with —M, (d@) —V with —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 himself 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 immersion: 
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 
