98 PROBLEMS OF EVOLUTION 



is not easy to recover. " In 1793 some w ^^ Scotch roses (R. 

 spinosissima) were transplanted into a garden ; and one of these 

 bore flowers slightly tinged with red, from which a plant was 

 raised with semi-monstrous flowers, also tinged with red ; seed- 

 lings from this flower were semi-double, and by continued selec- 

 tion, in about nine or ten years, eight sub-varieties were raised. 

 In the course of less than twenty years these double Scotch 

 roses had so much increased in number and kind that twenty-six 

 well marked varieties, classed in eight sections, were described 

 by Mr Sabine. In 1841 it is said that three hundred varieties 

 could be procured in the nursery gardens near Glasgow." * 



As with plants, so with animals, though in a less degree. 

 Domesticated breeds have to some extent lost their stability ; 

 change of condition stimulates variation ; in many cases their 

 characteristics are due to recent variations ; sometimes the breed 

 is the result of a cross, after which there is generally a tendency 

 to revert. In fact, when an organism varies it is a proof of 

 variability, and the tendency can only be kept down by rigorous 

 elimination. It is the characters that have become useless through 

 change of circumstances that are noted for their instability. In 

 Dorking fowls the colour of the plumage 2 and the form of 

 the comb have not been attended to ; hence has arisen a 

 variability not found in other species. Plenty more examples 

 might be quoted, but it is needless, as the phenomenon is 

 well known. 



There are, however, as shown in a previous section, 3 a 

 number of characters which, though apparently unimportant, 

 yet seldom vary, and whose constancy makes them valuable 

 to the systematist as specific distinctions. It is possible that 

 they may be protected by correlation with some adaptive char- 

 acters ; at any rate, they seem to stand in a class by themselves, 

 never having been important as adaptations. 



All the evidence would lead us to believe that Natural Selec- 

 tion is almost always required, except in the case of such 

 minutiae, to produce stability, and that when stability has been 



1 Darwin : Animals and Plants under Domestication, vol. i. p. 3^7- 



2 Ibid, vol. i. p. 270 ; vol. ii. pp. 159, 317. 3 See p. 77. 



