166 LAWS OF VARIATION. [Chap. V. 



Tandon gives a list of plants which, when growing 

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

 fleshy, though not elsewhere fleshy. These sHghtly va- 

 rying organisms are interesting in as far as they present 

 characters analogous to those possessed by the species 

 which are confined to similar 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 condi- 

 tions of life as different as can well be conceived; and, 

 on the other hand, of dissimilar varieties being produced 

 under apparently the same external conditions. Again, 

 innumerable instances are known to every naturalist, of 

 species keeping true, or not varying at all, although 

 living under the most opposite climates. Such con- 

 siderations as these incline me to lay less weight on 

 the direct action of the surrounding conditions, 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 con- 



