68 INSTINCTIVE BEHAVIOUR 
shall also admit some, nay much, variation in detail. Take, for 
example, two of the cases which Mr. Marshall cites—nest- 
building and migration. Both involve, not merely a simple 
response to a given stimulus, but a complex sequence of actions. 
In detail there may be much variation even among members of 
the same species. And yet, can it be questioned that the 
behaviour as a whole is in each case relatively definite ? May 
we not even say that it is remarkably definite? May we not 
even go further, and assert that only on the assumption that 
instinctive behaviour is relatively definite, can we regard it 
as a subject for scientific investigation, and can we hope to 
distinguish it from other modes of behaviour ? 
The next point for consideration in Spence’s definition, 
which we have taken as our text, is his characterization of 
instinctive acts as ‘“‘ tending to the well-being of the individual 
and the preservation of the species.” Here we have Mr. 
Marshall with us, for he too lays stress on the fact that 
instinctive behaviour has reference to a definite biological end. 
But in saying that the biological end is the objective mark of 
an instinct,* he seems to bein error. Because, in the first place, 
there are other “ objective marks,” and because, in the second 
place, this objective mark is not restricted to instinctive 
behaviour. According to Spence, a further characteristic of 
instinctive acts is that they are independent of instruction or 
experience ; and this serves to differentiate them from other 
modes of behaviour which are also subservient to a biological 
end. Intelligent behaviour, not less than that which we term 
instinctive, has reference to a biological end. Many intelligent 
acts, for example, have for their object the well-being of the 
individual ; many subserve race preservation ; these bear, every 
whit as much as instinctive acts, the ‘‘ objective mark” which 
Mr. Marshall regards as characteristic of instinct. And if we 
turn to his subjective criterion—the absence of any conception 
of the biological end which the behaviour subserves—Mr. 
Marshall’s position is equally untenable. There are thousands 
of acquired modes of behaviour, dependent on instruction or 
* « Instinct and Reason,” p. 91. 
