Indeed the instinct persists when it is obviously useless, as in the case of a dog who turns round to flatten the grass before lying down on a carpet; and even when it is known to be dangerous, as when a man recovering from typhoid hungers for solid food.
[4] 'Instinct is usually defined as the faculty of acting in such a way as to produce certain ends without foresight of the ends and without previous education in the performance.'-- W.

James, _Principles of Psychology_, vol.ii.p.

383.
The fact that impulse is not always the result of conscious foresight is most clearly seen in the case of children.

The first impulses of a baby to suck, or to grasp, are obviously 'instinctive.' But even when the unconscious or unremembered condition of infancy has been succeeded by the connected consciousness of childhood, the child will fly to his mother and hide his face in her skirts when he sees a harmless stranger.
Later on he will torture small beasts and run away from big beasts, or steal fruit, or climb trees, though no one has suggested such actions to him, and though he may expect disagreeable results from them.
We generally think of 'instinct' as consisting of a number of such separate tendencies, each towards some distinct act or series of acts.
But there is no reason to suppose that the whole body of inherited impulse even among non-human animals has ever been divisible in that way.

The evolutionary history of impulse must have been very complicated.