192 THE ORIGIN OF SPECIES 



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 accumulative 

 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 tho 

 warmest-clad individuals having been favored and pre- 

 served 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 domes- 

 tic quadrupeds. 



Instances could be given of similar varieties being 

 produced from the same species under external conditions 

 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, innu- 

 merable instances are known to every naturalist of 

 species keeping true, or not varying at all, although 

 living unvier the most opposite climates. Such considera- 

 tions 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 condi- 

 tions determine whether this or that variety shall survive. 

 But when man is the selecting agent, we clearly see that 

 the two elements of change are distinct; variability is in. 



