46 THE DARWINIAN THEORY 



such as nutrition, cold, &c, and these may affect 

 the young, or even the embryo, or the egg before 

 it is laid by the parent. No two animals can 

 ever come into existence under absolutely identical 

 conditions ; neither can any two after birth be ex- 

 posed to absolutely the same conditoins. 



Variation under domestication is the rule instead 

 of the exception, and occurs more or less in every 

 direction. Consider, for instance, the extraordinary 

 variations in size and mode of growth of the 

 cabbage ; the solid heads of foliage utterly unlike 

 any plant in a state of Nature; the curiously wrinkled 

 leaves of the savoy, the purple leaves of the pickling 

 cabbage, the compact heads of flowers of the 

 broccoli and cauliflower, the curious stem of the 

 Kohlrabi, which grows like a turnip. Again, of the 

 apple there are at least a thousand varieties known, 

 all descended from the common crab-apple. In fact, 

 as Wallace says, "there is hardly an organ or a 

 quality in plants or animals which has not been 

 observed to vary ; and further, whenever any of 

 these variations have been useful to man, he has 

 been able to increase them to a marvellous extent 

 by the simple process of always preserving the best 

 varieties to breed from." 



Limits to variation must of course exist, and it is 

 evident that up to some point or other variations 

 must be predetermined on definite lines. The 

 inconstancy of chemical composition or instability 

 is specially characteristic of living things. Varia- 

 tions are spoken of as accidental, not in the sense 

 of their not being all due to natural causes, but 



