426 Mental Factors in Evolution 
evolution rendered possible. Such is the logical outcome of Darwin’s 
teaching. 
Those who abide by the cardinal results of this teaching are 
bound to regard all behaviour as the expression of the functional 
activities of the living tissues of the organism, 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. Sub- 
ordinate 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 ex- 
perience 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 distinguish- 
able: 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’, “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 
1 Origin of Species (6th edit.), p. 205. 
