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assistance which is often rendered. Different species of 
animals, as we have already seen, often live together, 
rendering mutual assistance and reaping a common 
advantage; and there seems no reason why individual 
members of different species should not do the same. 
The difference which distinguishes them may only serve to 
enhance the attraction of the mutual affection or the value 
of the mutual service. 
There are certain actions which may be described as 
tricks of manner. “ Scarcely any two sporting dogs point 
in exactly the same manner, although every dog adheres 
to his particular attitude through life.”* But this is only 
to say that as no two individuals are exactly alike, so also 
their actions are not exactly alike. Such differences may 
therefore be regarded as the inevitable result of differences 
of organisation. So long as such differences do not affect 
the usefulness of the action, they are of no practical value. 
The mannerism of the sporting dog need not lessen its 
efficiency. If the pointer moves stealthily and without 
noise in the direction of the game ; if it stops at that 
point where it would be fatal to its purpose to go further; 
if it stands like a statue with uplifted foot and outstretched 
tail, it fulfils all the necessary functions of its art; and it 
is immaterial to the sportsman so long as it does all this, 
whether or no it does it with a gait and manner of its 
own. Moreover, it is quite possible that individual differ 
ences may be useful for purposes of recognition. We can 
tell one man from another by the tread of his footstep, 
by the tone of his voice, by a characteristic cough, even 
if we do not see him. If we see him, we can tell by his 
gait who he is, even when he is at a considerable distance. 
How inconvenient it would be not to recognise one 
Mental Evolution in Animals, pp. 181-2.