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ON THE EXCITING CAUSES OF VARIETIES IN BIRDS AND 
OTHER ANIMALS. 
By Neville Wood, Esq. 
In various numbers of The Naturalist , correspondents have recorded instances 
of varieties in birds and other animals which have fallen under their observation, 
or come to their knowledge. In the present paper we propose briefly to explain 
our views respecting the exciting causes of these curious modifications. 
The Common Fowl ( Gallus domesticus , Auct., Pkasianus gallus , Linn.), 
originally derived fr :m Asia, is now scarcely known in its native haunts; but 
has long been extensively cultivated as a domestic bird in almost every country. 
What influence may be drawn from these facts ? Now we are of opinion, that, 
cceteris paribus , the more thoroughly and the longer any animal is domesticated, 
and the more the domesticated differs from the wild state, the more subject will 
that animal be to variety, and the more remarkable will the varieties be. Both 
arguments and facts fully support this theory ; and what we at first considered a 
mere hypothesis, has at length ripened into a matter of demonstration. 
Thus, varieties of birds inhabiting extensive tracts of fen-land, wflde and arid 
plains, or the summits of bleak mountains, little frequented by Man, are seldom 
noticed, because they rarely occur. The ordinary changes of plumage, termed 
moulting, there take place with almost unerring regularity, as, for instance, in 
the various Ptarmigans of the hill-top, the Waders ( Grallatores) of the moist 
and sedgy river-side, the Petrels, Ducks, and Gulls of the “ wild unbounded 
sea,” &c. All these, and many others, live strictly according to their nature. 
A second class furnishes the collecting naturalist with occasional varieties. 
Thus the Wild Duck ( Anas bosckas, Linn.), which abounds throughout the year 
in the fresh waters of Britain, is necessarily partially, though but little, under 
the jurisdiction of Man. Varieties are accordingly occasionally met with, from 
the dark rich colour of the natural state to a chocolate hue, or even pure white. 
The Partridge belongs to the same division, and yields an occasional variety. 
The Pheasant and the House Sparrow depend still more upon our bounty and 
our works, and hence varieties are tolerably frequent in these species, though not 
very much so, considering the great abundance of these birds in almost every part 
of the country. Sparrows occur black, white, and cream-coloured, and the 
varieties of the Pheasant—an imported species, and half domesticated—are still 
more frequent and diverse. 
Lastly, we come to the wholly-domesticated races of birds. In the two 
former classes the varieties form the exceptions to a general rule; but here the 
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