An impulse which survived because it produced one result may have persisted with modifications because it produced another result; and side by side with impulses towards specific acts we can detect in all animals vague and generalised tendencies, often overlapping and contradictory, like curiosity and shyness, sympathy and cruelty, imitation and restless activity.

It is possible, therefore, to avoid the ingenious dilemma by which Mr.Balfour argues that we must either demonstrate that the desire, _e.g._ for scientific truth, is lineally descended from some one of the specific instincts which teach us 'to fight, to eat, and to bring up children,' or must admit the supernatural authority of the Shorter Catechism.[5] [5] _Reflections suggested by the New Theory of Matter_, 1904, p.

21.
'So far as natural science can tell us, every quality of sense or intellect which does _not_ help us to fight, to eat, and to bring up children, is but a by-product of the qualities which do.' The pre-rational character of many of our impulses is, however, disguised by the fact that during the lifetime of each individual they are increasingly modified by memory and habit and thought.

Even the non-human animals are able to adapt and modify their inherited impulses either by imitation or by habits founded on individual experience.

When telegraph wires, for instance, were first put up many birds flew against them and were killed.