n the more
strictly Darwinian and the Lamarckian principles of interpretation.
But it is not in any sense a compromise. The principle of
interpretation of that which is instinctive and hereditary is wholly
Darwinian. It is true that some of the facts of observation relied
upon by Lamarckians are introduced. For Lamarckians however the
modifications which are admittedly factors in survival, are regarded
as the parents of inherited variations; for believers in organic
selection they are only the foster-parents or nurses. It is because
organic selection is the direct outcome of and a natural extension of
Darwin's cardinal thesis that some reference to it here is
justifiable. The matter may be put with the utmost brevity as follows:
(1) Variations (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

(_b_) + V with - M, (_c_) - V with + M,

(_a_) + 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 there 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
necessary to link more closely biologica