It would be easy to show that several distinct mental actions are commonly embraced by this term; but every one understands what is meant, when it is said that instinct impels the cuckoo to migrate and to lay her eggs in other birds' nests.
Frederick Cuvier and several of the older metaphysicians have compared instinct with habit.
Under changed conditions of life, it is at least possible that slight modifications of instinct might be profitable to a species; and if it can be shown that instincts do vary ever so little, then I can see no difficulty in natural selection preserving and continually accumulating variations of instinct to any extent that may be profitable.
No complex instinct can possibly be produced through natural selection, except by the slow and gradual accumulation of numerous, slight, yet profitable, variations.
Again as in the case of corporeal structure, and conformably with my theory, the instinct of each species is good for itself, but has never, as far as we can judge, been produced for the exclusive good of others.
I can only assert, that instincts certainly do vary--for instance, the migratory instinct, both in extent and direction, and in its total loss.
But 'Pilgrim's Progress,' let it be said frankly, will always find a dozen readers where Milton has one by choice, and no man can afford to think otherwise than respectfully of achievements which speak powerfully and nobly to the underlying instincts
and needs of all mankind.
That peculiar instinct could hardly be called a weakness.
But in any case, Chief Inspector Heat, purveyor of prisons by trade, and a man of legal instincts, did logically believe that incarceration was the proper fate for every declared enemy of the law.
It required nearly a fortnight for fine instinct
to assure itself of these inspirations; indeed, it was a whole week before Stephen's letter came, telling his father the facts, and adding that he was gone across to Holland,--had drawn upon the agent at Mudport for money,--was incapable of any resolution at present.