1884 .] 
Theory of Evolution . 187 
As regards the first assertion it is, of course, refuted by 
all the very numerous instances where hybrids have been 
produced without any human aid or contrivance. But there 
are, further, cases almost innumerable of intercourse be- 
tween animals of widely different species where no offspring 
has been known to result. Thus there is on record (“ Ame- 
rican Naturalist,” xvii., 359) the long-continued intimacy of 
a male elk with a Durham heifer. A stag has been known 
to pair with cows in Scotland. The present writer once 
saw, in Austrian Silesia, a hound copulating with an ewe, 
and was told that this was a very common action on the 
part of the dog. A Newfoundland dog has been known to 
have intercourse with a sow. Without needlessly multi- 
plying further examples I may lay down, as a counter- 
proposition based upon faCts, that — 
“ Male animals, without human interference, will, in 
default of a mate of their own species, pair with any 
female not too dissimilar from themselves in size, 
structure, and habits.” 
Let us turn to the second proposition. The number of 
hybrid forms which have been produced is so great that 
their birth cannot be regarded as an abnormal result. Mac- 
gillivray, as quoted by Darwin in the “ Descent of Man,” 
gives an instance of a male blackbird which paired with a 
female thrush, and produced a family of young birds. The 
great wood-grouse ( Tetrao urogallus) very commonly espouses 
the black hen ( T . tetrix), and the hybrids sprung from this 
alliance have been recognised as a distinct species under the 
name of Tetrao medius, and in some districts are, according 
to Semper, superseding the pure strain of black game ; 
whence it may be fairly concluded that T. medius is not in- 
capable of reproduction. In the gardens of the Paris 
“ Society of Acclimatisation ” there are, or were in 1882, 
two male hybrids, one between a Houdan cock and a Guinea 
hen, and the other between a Cochin China cock and a turkey 
hen. According to Darwin ( opus citat., p. 414) eighteen cases 
have been recorded, in Great Britain alone, of hybrids be- 
tween the black grouse and the pheasant. A wild duck has 
been known to nest with a male pintail, and rear a brood of 
seven or eight hybrid ducklings. According to Rev. W. D. 
Fox ( ibidem ) “ a pair of Chinese geese ( Anser cygnoides) were 
placed on the same pond with a common gander and three 
geese. The result was that of the young birds hatched from 
the eggs of the common geese only four were pure, the other 
eighteen proving hybrids.” 
