aviour is adaptive on the first occurrence
of the appropriate presentation; in the latter case accommodation to
circumstances is only reached after a greater or less amount of acquired
organic modification of structure, often accompanied (as we assume) in
the higher animals by acquired experience. Logically and biologically
the two classes of behaviour are clearly distinguishable: but the
analysis of complex cases of behaviour where the two factors cooperate,
is difficult and requires careful and critical study of life-history.

The foundations of the mental life are laid in the conscious experience
that accompanies those modes of behaviour, dependent entirely on racial
preparation, which may broadly be described as instinctive. In the
eighth chapter of "The Origin of Species" Darwin says ("Origin of
Species" (6th edition), page 205.), "I will not attempt any definition
of instinct... 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. An action, which we ourselves require experience to enable
us to perform, when performed by an animal, more especially by a very
young one, without experience, and when performed by many individuals in
the same way, without their knowing for what purpose it is performed, is
usually said to be instinctive." And in the summary at the close of the
chapter he says ("Origin of Species" (6th edition), page 233.), "I have
endeavoured briefly to show that the mental qualities of our domestic
animals vary, and that the variations are inherited. Still more briefly
I have attempted to show that instincts vary slightly in a state of
nature. No one will dispute that instincts are of the highest importance
to each animal. Therefore there is no real difficulty, under changing
conditions of life, in natural selection accumulating to any extent
slight modifications of instinct which are in any way useful. In many
cases habit or use and disuse have probably come into play."

Into the details of Darwin's treatment there is neither space nor need
to enter. There are some ambiguous passages; but it may be said that for
him, as for his followers to-day, instinctive behaviour is wholly the
result of racial preparation transmitted through organic heredity. For
the performance of the instinctive act no individual preparation under
the guidance of personal experience is necessary. It is true that Darwin
quotes with approval Hube