NATURAL AND ARTIFICIAL VARIETIES 177 



been long cultivated, they are of frequent occurrence. This con- 

 clusion explains a curious discrepancy : Max Wichura, who worked 

 exclusively on willows which had not been subjected to culture, 

 never saw an instance of reversion ; and he goes so far as to 

 suspect the careful Gartner had not sufficiently protected his 

 hybrids from the pollen of the parent species. Naudin, on the other 

 hand, who chiefly experimented on cucurbitaceous and other culti- 

 vated plants, insists more strenuously than any other author on the 

 tendency to reversion in all hybrids. The conclusion that the 

 condition of the parent-species, as affected by culture, is one of the 

 proximate causes leading to reversion, agrees well with the converse 

 case of domesticated animals and cultivated plants being liable to 

 reversion when they become feral ; for in both cases the organiza- 

 tion or constitution must be disturbed, though in a very different 

 way." * 



294. We are driven then to the conclusion that Natural and 

 Artificial selection are essentially unlike. Nature and man do not 

 select the same class of characters. Man, perforce, chooses 

 mutations. Nature, with finer powers of discrimination and with 

 unlimited time and material at her disposal, chooses, perhaps with 

 very rare exceptions, fluctuating variations. In no other way is it 

 possible to account for the striking differences revealed when natural 

 and artificial varieties are crossed. It is known that man tends to 

 select mutations, and that the reproduction of mutations tends to 

 be alternative. It is clear that when reproduction is alternative, 

 characters tend to become latent, and when latent to become patent 

 in cross-breeding. If, then, as experimental workers suppose, nature 

 chooses mutations, how does it happen that natural varieties, when crossed, 

 not only blend very often, but hardly ever reveal latent characters ? 2 



295. The fact that natural varieties often blend their characters 



1 Animals and Plants, vol. ii. pp. 24-5. 



2 Since latent characters are in effect found only in domesticated varieties, it 

 follows that Darwin, who drew the materials on which his conclusion was founded 

 wholly from artificial varieties, formulated too wide an inference when he declared 

 that, " besides the visible changes which it [the germ] undergoes, we must believe 

 that it is crowded with invisible characters, proper to both sexes, and to both the 

 right and left side of the body, and to a long line of male and female ancestors 

 separated by hundreds or even thousands of generations from the present time ; and 

 that these characters, like those written on paper with invisible ink, lie ready to be 

 evolved whenever the organization is disturbed by certain known or unknown 

 conditions " (Animals and Plants, vol ii. pp. 35-6). It follows, also, that Professor 

 de Vries is mistaken in defining a variety as a type which has patent or latent a 

 character which is in the opposite condition in the parent species. A type which 

 carries a latent character is always a mongrel ; for it is only when varieties possess- 

 ing alternative characters cross, that latency occurs. Thus, all sexually dimorphic 



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