HEREDITY, VARIATION 



121 



Per cent. 



Nose length 9.46 



" breadth 7.57 



'' height 15.2 



Forehead height 10.4 



Under-jaw length 4.81 



Mouth bretidtJi 5.18 



Per cent. 



Head length 2.44 



" breadth 2.78 



Upper arm length G.50 



Fore arm length 3.85 



Upper leg length 5.00 



Lower " 5.04 



Foot length 5.92 



Here we see that the different parts of the human body vary 

 more, proportionally, than does its whole height ; and we must 

 always remember that these variations are all, to a large extent, 

 independent of each other, just as we saw was the case with 

 those parts shown in the bird diagram. 



Again Ave must lay stress upon the fact that every part of 

 every organism, outside or inside, important or insignificant, 

 is subject to a similar and often more pronounced amount of 

 variation, as numerous examples quoted in Mr. Vernon's book 

 amply prove. So that we are fully justified in accepting as a 

 demonstrated fact, that the whole structure of every organism, 

 in every stage of its growth or development, varies in its dif- 

 ferent individuals, each one in a somewhat different manner, 

 and to such a large extent as to afford the amplest store of 

 material for modification and development in any direction 

 that may be required. 



This ever-present and all-pei"vading variability is probably 

 the most important of the contributory factors of evolution, 

 and must never for a single moment be lost sight of. 



Powers of Increase of Plants and Animals 



Of almost equal importance with ever-present variation is 

 the power which all organisms possess of reproducing their 

 kind so rapidly as to be able to take possession of any unoc- 

 cupied spaces around them, and in many cases to expel other 

 kinds by the vigour of their growth. 



The rapidity of increase is most prominently seen among 

 vegetables. These are capable, not only of a fivefold nr ten- 

 fold annual increase, as am<^iii:- many of the higher animals, 



