Correlation 
Natural selection deals with an organism as a 
whole. Its effect is to permit those creatures to 
survive which, taken as a whole, are best adapted 
to their environment. 
Physiologists insist with ever-increasing em- 
phasis that there is more or less correlation and 
inter-connection between the various parts of an 
organism. 
The several organs of an animal are not so 
many isolated units. It is impossible to act on 
one organ without affecting some or all of the 
others. 
Variations in a given direction of one organ 
are usually accompanied by correlated variations 
in some of the other organs. If strength be of 
paramount importance to an animal, natural 
selection will tend to preserve those individuals 
which exhibit strength to a marked degree, and 
this exhibition of strength may be accompanied 
by other peculiarities, such as short legs or a 
certain colour, so that natural selection will 
indirectly tend to produce individuals with short 
legs and having the colour in question, and it 
may happen that this particular colour is one 
that renders the animal more conspicuous than 
the normal colour does. Nevertheless, on account 
of the all-needful strength which accompanies it, 
those animals so coloured may survive while 
those of a more protective hue perish. Thus, 
paradoxical though it seems, natural selection 
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