390 ON SPECIES AND RACES, AND THEIR ORIGIN 
he considers that causes essentially similar to those which have given 
rise to these birds are operative in nature now, and have in past times 
been the agents in producing all the species we know. If neither of 
these positions can be upset, Mr. Darwin’s must be regarded as a true 
theory of species, as well based as any other physical theory: they 
require, therefore, the most careful and searching criticism. 
after pointing out the remarkable differences in structure and 
habits between the Carrier, Pouter, Fantail, Tumbler, and the wild 
Columba livia, the speaker expressed his entire agreement with 
Mr. Darwin’s conclusion, that all the former domesticated breeds had 
arisen from the last-named wild stock ; and on the following grounds— 
1. That all interbreed freely with one another. 2. That none of the 
domesticated breeds presents the slightest approximation to any wild 
species but C. /¢zza, whose characteristic markings are at times ex- 
hibited by all. 3. That the known habits of the Indian variety of the 
Rock Pigeon (C. zz¢erimedia) render its domestication easily intelligible 
4. That existing varieties connect the extremest modifications of the 
domestic breeds by insensible links with C. “via. 5. That there is 
historical evidence of the divergence of existing breeds, eg., the 
Tumbler, from forms less unlike C. Zvza. 
The speaker then analyzed the process of selection by which the 
domesticated breeds had been produced from the Wild Rock Pigeon ; 
and he showed its possibility to depend upon two laws which hold 
good for all species, viz., 1. That every species tends tovary. 2. That 
variations are capable of hereditary transmission. The second law is 
well understood ; but the speaker adverted to the miscomprehension 
which appears to prevail regarding the first, and showed that the 
variation of a species is by no means an adaptation to conditions in 
the sense in which that phrase is commonly used. Pigeon-fanciers 
in fact, subject their pigeons to a complete uniformity of conditions ; 
but while the similarly used feet, legs, skull, sacral vertebra, tail 
feathers, oil gland and crop undergo the most extraordinary modifi- 
cations ; on the other hand, the wings, whose use is hardly ever per- 
mitted to the choice breeds, have hitherto shown no sign of diminution. 
Man has not as yet been able to determine a variation; he only 
favours those which arise spontaneously, ze, are determined by 
unknown conditions. 
It must be admitted that, by selection, a species may be made to 
give rise experimentally to excessively different modifications; and 
the next question is: Do causes adequate to exert selection exist 
in nature? On this point, the speaker referred his audience to 
