anism, and all conscious experience as
correlated with such activities. For the purposes of scientific
treatment, mental processes are one mode of expression of the same
changes of which the physiological processes accompanying behaviour
are another mode of expression. This is simply accepted as a fact
which others may seek to explain. The behaviour itself is the adaptive
application of the energies of the organism; it is called forth by
some form of presentation or stimulation brought to bear on the
organism by the environment. This presentation is always an individual
or personal matter. But in order that the organism may be fitted to
respond to the presentation of the environment it must have undergone
in some way a suitable preparation. According to the theory of
evolution this preparation is primarily racial and is transmitted
through heredity. Darwin's main thesis was that the method of
preparation is predominantly by natural selection. Subordinate to
racial preparation, and always dependent thereon, is individual or
personal preparation through some kind of acquisition; of which the
guidance of behaviour through individually won experience is a typical
example. We here introduce the mental factor because the facts seem to
justify the inference. Thus there are some modes of behaviour which
are wholly and solely dependent upon inherited racial preparation;
there are other modes of behaviour which are also dependent, in part
at least, on individual preparation. In the former case the behaviour
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 cooeperate, 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,[160] "I will not attempt any definition of instinct.... Every
one understands what is meant, when it is said that instinct impels
the cuckoo to