128 REDUCTION OF VARIABILITY. 



In new conditions of life, in a new environment, possibilities 

 may be open that were not so before. An organ which may 

 have had an important tunction, may now be useless. There- 

 fore, if formerly only individuals having the organ in a certain 

 state of development could live, in the new conditions tolera- 

 tion will be great on this point, and if genes affecting the devel- 

 opment of the organ are recombined, the final type of the new 

 species may have the organ greatly changed. It may now be 

 larger or smaller or altogether rudimentary without hindering 

 an otherwisely well-adapted species from procreating itself. 



The disappearance of unused organs may in some instances 

 be thus explained. But this is a rather complicated question. 



In the first place it must be remembered that no organ is as 

 such determined in the germ. To its development very many 

 factors cooperate, of which some are inherited and some are 

 not. Functions are very important developmental factors. A 

 functionless organ may in many cases remain rudimentary 

 for the very reason that it is without function. If we regard the 

 heavy fore-legs, and the strong musculature of the neck of the 

 bull-moose, we may assume that these adaptations to the great 

 weight of the antlers are in some way inherited. But we may 

 also try to find out whether this musculature is not to a great 

 extent caused in every individual male-moose by the weight of 

 the antlers. If we gradually weigh the head. of a young horse 

 with shot, until it bears the weight of a moose's antlers, it may 

 be that the musculature of its back will closely approximate 

 that of a bull-moose. 



Carnivorous animals have a very much shorter alimentary 

 tract than herbivores. This is an adaptation to the special diet. 

 But feeding experiments with geese and tadpoles and ducks 

 have shown, that the length of the alimentary tract depends 

 very largely upon the diet of the developing individual. 



In those cases where we observe an anatomical peculiarity 

 adapted to a peculiar habit or mode of life, it is very difficult to 

 see clearly whether the anatomical character was gradually 

 evolved by selection to meet the requirements of the habit, or 



