THE METHOD OF ORGANIC EVOLUTION. 433 



of stability. Such are the light and dark colored varieties in many 

 insects and in some nianinials and birds, the hairy or smooth varieties 

 of plants, specially banded or colored land shells, and many others. 

 Whenever any of these variations are not injurious under the actual 

 conditions of existence of the species they may i^ersist in considerable 

 numbers, and thus appear to be stable. But others which are compar- 

 atively rare may be just as stable organically, as shown by the case 

 of white mice, pigeons, etc., which increase to any extent under domes- 

 tication. In a wild state they rever do so, and the obvious reason 

 is that either the conspicuous color 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 proba- 

 bility, various degrees of hurtfulness. If in any case the white color 

 were not at all injurious as compared with that of the type, it would 

 almost alwaj^s, by the operation of Delboeuf's law, tend to increase to 

 nearly an eciuality 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 number 

 of individuals i)resenting these discontinuous variations, we may there- 

 fore draw an important conclusion which has hitherto been overlooked. 

 It is that not only do such variations afford no support to the theory 

 of a special "organic stability" capable of producing races, species, 

 and even genera, without any aid from natural selection, but they fur- 

 nish a strong, if not conclusive, argument against it, since any which 

 did i)ossess such exceptional stability and were in no degree injurious 

 would long since have become equal in numbers to the type of the 

 species. 



A few words are here necessary as to the very common misconcep- 

 tion that extreme Darwinians do not recognize the importance of the 

 organism itself and of its laws of growth and development in the proc- 

 ess of evolution. For myself, I may say that no one can be more 

 profoundly impressed by the vast range, by the complexity, by the mys- 

 tery, by the marvelous power of the laws and i)roperties of organized 



'For a statement and popular demonstration of DeTbcenf's law see Habit and 

 Intelligence, by J. J. Muriihy, 2d ed., page 241. Brielly, the law is that if a species 

 produces a variety, in liowever small a proportion annually, and if the variety pro- 

 duces its like in the same proportion as docs the species, and if it is neither bene- 

 ficial nor hurtful to the species, then the variety will increase, rapidly at first and 

 more slowly afterwards, till it approaches to ecxuality in numbers with the species. 

 From this law it follows that, as varieties are usually very much less numerous than 

 the species, this must be due to one of the following causes: Either (1) the variety 

 has but recently originated, and has not had time to increase, or (2) the variety has 

 ceased to be produced by the species, or (3) it does not reproduce its like so com- 

 pletely as does the species, or (4) it is disadvantageous to the species. The first two 

 suppositions are improbable, and can only account for a very small proportion of the 

 varieties which are greatly inferior iu numbers to the species; the other two are 

 antagonistic to any si)e<ial "organic stabilitj'," which must therefore, in the great 

 majority of cases, be rejected as being both unproven and opposed to the facts. 



SM 91 28 



