166 LAWS OF VAKIATION". [Chap. V 



landon gives a list of plants which, when growing 

 near the sea-shore, have their leaves in some degree 

 fleshy, though not elsewhere fleshy. These slightly 

 varying organisms are interesting in as far as they 

 present characters analogous to those possessed by the 

 species which are confined to similiar conditions. 



When a variation is of the slightest use to any being, 

 we cannot tell how much to attribute to the accumula- 

 tive action of natural selection, and how much to the 

 definite action of the conditions of life. Thus, it is well 

 known to furriers that animals of the same species 

 have thicker and better fur the further north they 

 live ; but who can tell how much of this difference 

 may be due to the warmest-clad individuals having 

 been favoured and preserved during many generations, 

 and how much to the action of the severe climate ? for 

 it would appear that climate has some direct action on 

 the hair of our domestic quadrupeds. 



Instances could be given of similar varieties being 

 produced from the same species under external con- 

 ditions of life as different as can well be conceived; 

 and, on the other hand, of dissimilar varieties being 

 produced under apparently the same external con- 

 ditions. Agjain, innumerable instances are known to 

 every naturalist, of species keeping true, or not varying 

 at all, although living under the most opposite climates. 

 Such considerations as these incline me to lay less 

 weight on the direct action of the surrounding con- 

 ditions, than on a tendency to vary, due to causes of 

 which we are quite ignorant. 



In one sense the conditions of life may be said, not 

 only to cause variability, either directly or indirectly, 

 but likewise to include natural selection, for the 



