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or selected for three thousand years. Mr Darwin took two of the 
unlikest and most aberrant parents he could select, a black “ barb” 
and a white “ fantail.” The result was, that a grandchild of these 
parents exhibited a close return to the old primal type, the rock- 
pigeon, from which all domestic pigeons originally sprung. Yet 
who knows through how many generations of “ selected parents” — 
perhaps from the days of the Pharaohs — this chick had inherited its 
ancestral colours ! Can there be a stronger illustration of that 
restraining law of reversion to type, which, so far as we know, con- 
fines within a very narrow circle, not only the extent, but the dura- 
tion of aberrant forms of life? Then, as regards natural selection, 
do we know of any one authentic instance in which new conditions 
of life have been met by such modifications of structure as might 
enable an animal to survive its congeners in the “ battle of life ?” 
Our experience in this way is perhaps fully more extensive than in 
any other. The truth is, that man is himself the greatest modifier 
of the natural conditions under which the lower animals are placed. 
He is year by year producing revolutions which might be equivalent 
to centuries of natural change. Nor are these without a powerful 
effect on animal life. Mr Darwin has traced the changes thus pro- 
duced with singular ingenuity and beauty of description. But all 
those changes are produced by the substitution of one species for 
another, — never by the modification of the same species to the new 
conditions which surround it. There need be no dispute that, under 
the law so beautifully traced by Darwin, such modifications, if they did 
arise , would tend to survive and be perpetuated. But what we want 
is — facts to justify the supposition that any such modifications do actu- 
ally arise ; such, for example, as would enable an animal adapted for 
marshy land to survive on land which had become dry ; — or arboreal 
forms to survive the destruction of their native forests ; — or land- 
animals to adapt themselves to a country which is being gradually 
submerged. These are all operations of which man has had expe- 
rience, and to some of which he is every day contributing ; yet no 
instance is recorded of nature having ever had any opportunity of 
exercising in favour of any animal that “selecting” power which is 
the assumed origin of new species. The Fauna is indeed changed by 
such changes of condition as I have supposed. But that change is 
effected by substitution, not by conversion. One animal or plant in- 
VOL. iv. 3 D 
