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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