374 STUDIES, SCIENTIFIC AND SOCIAL caAP. 



origin of the genera and species of living organisms. A 

 study of the distribution of the stars over the surface of 

 the heavens, or of the interlacing ripple-marks upon the 

 sea-beach, would no doubt show tliat these objects might 

 also be the subject of classification; and from the point 

 of view of elucidating the origin of species, they would 

 be about as useful, or as worthless, as the study of finger- 

 marks. 



Of course, there are many varieties or races, both among 

 animals and plants, which continually reappear, and which 

 in some cases are known to reproduce their like, and these 

 undoubtedly have an appearance of stability. Such are 

 the light and dark-coloured varieties in many insects and 

 in some mammals and birds ; the hairy or smooth varieties 

 of plants ; specially banded or coloured land-shells, and 

 many others. Whenever any of these variations are not 

 injurious under the actual conditions of existence of 

 the species, they may persist in considerable numbers, 

 and thus appear to be stable. But others which are com- 

 paratively rare may be just as stable organically, as shown 

 by the case of white mice, pigeons, &c., which increase to 

 any extent under domestication. In a wild state they 

 never do so, and the obvious reason is, that either the 

 conspicuous colour, or something correlated with it, is 

 injurious. In flowers white varieties are frequent, and 

 they occur in all degrees of abundance or rarity ; and this 

 indicates, in all probability, various degrees of hurtful- 

 ness. If in any case the white colour were not at all 

 injurious as compared with that of the type, it would 

 almost always, by the operation of Delboeufs Law, tend 

 to increase to nearly an equality with the parent form ; 

 and as this equality so rarely occurs, we must conclude 

 that, in most cases, the variety (of whatever kind) is to 

 some extent injurious.^ From the usually limited num- 



^ For a statement and popular demonstration of Delbceuf's Law, see 

 Habit and bifel/iirence, by J. J. Murphy, 2nd Ed., p. 24L Briefly, the 

 law is, that, if a species produces a variety, in however small a propor- 

 tion annually, and if the variety produces its like in thesanie pi'oportion 

 as does the species, and if it is neither beneficial nor hurtful to the 

 s pecies, then the variety will increase, rapidly at first and more slowly 

 afte rwards, till it approaches to equality in numbers with the species. 



