h 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. 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. But although the number of those that were killed
was obviously insufficient to produce a change in the biological
inheritance of the species, very few birds fly against the wires now.
The young birds must have imitated their elders, who had learnt to avoid
the wires; just as the young of many hunting animals are said to learn
devices and precautions which are the result of their parents'
experience, and later to make and hand down by imitation inventions of
their own.

Many of the directly inherited impulses, again, appear both in man and
other animals at a certain point