154 
DARAVINISM 
CHAP. 
and numbers of species of rodents, very rarely breed in 
confinement; while other species do so more or less freely. 
Hawks, vultures, and owls hardly ever breed in confinement; 
neither did the falcons kept for hawking ever breed. Of the 
numerous small seed-eating birds kept in aviaries, hardly 
any breed, neither do parrots. Gallinaceous birds usually 
breed freely in confinement, but some do not; and even 
the guans and curassows, kept tame by the South American 
Indians, never breed. This shows that change of climate has 
nothing to do with the phenomenon ; and, in fact, the same 
species that refuse to breed in Europe do so, in almost every 
case, when tamed or confined in their native countries. This 
inability to reproduce is not due to ill-health, since many 
of these creatures are perfectly vigorous and live very long. 
With our true domestic animals, on the other hand, 
fertility is perfect, and is very little affected by changed 
conditions. Thus, we see the common fowl, a native of 
tropical India, living and multiplying in almost every part of 
the world ; and the same is the case wdth our cattle, sheep, 
and goats, our dogs and horses, and especially with domestic 
pigeons. It therefore seems probable, that this facility for 
breeding under changed conditions was an original property 
of the species which man has domesticated — a property 
which, more than any other, enabled him to domesticate them. 
Yet, even with these, there is evidence that great changes of 
conditions affect the fertility. In the hot valleys of the 
Andes sheep are less fertile ; while geese taken to the high 
plateau of Bogota were at first almost sterile, but after some 
generations recovered their fertility. These and many 
other facts seem to show that, with the majority of animals, 
even a slight change of conditions may produce infertility or 
sterility; and also that after a time, when the animal has 
become thoroughly acclimatised, as it were, to the new 
conditions, the infertility is in some cases diminished or 
altogether ceases. It is stated by Bechstein that the canary 
was long infertile, and it is only of late years that good 
breeding birds have become common; but in this case no 
doubt selection has aided the change. 
As showing that these phenomena depend on deep-seated 
causes and are of a very general nature, it is interesting 
