ls have been modified by domestication. It is scarcely possible to
doubt that the love of man has become instinctive in the dog. All wolves,
foxes, jackals, and species of the cat genus, when kept tame, are most
eager to attack poultry, sheep, and pigs; and this tendency has been found
incurable in dogs which have been brought home as puppies from countries,
such as Tierra del Fuego and Australia, where the savages do not keep these
domestic animals. How rarely, on the other hand, do our civilised dogs,
even when quite young, require to be taught not to attack poultry, sheep,
and pigs! No doubt they occasionally do make an attack, and are then
beaten; and if not cured, they are destroyed; so that habit, with some
degree of selection, has probably concurred in civilising by inheritance
our dogs. On the other hand, young chickens have lost, wholly by habit,
that fear of the dog and cat which no doubt was originally instinctive in
them, in the same way as it is so plainly instinctive in {216} young
pheasants, though reared under a hen. It is not that chickens have lost all
fear, but fear only of dogs and cats, for if the hen gives the
danger-chuckle, they will run (more especially young turkeys) from under
her, and conceal themselves in the surrounding grass or thickets; and this
is evidently done for the instinctive purpose of allowing, as we see in
wild ground-birds, their mother to fly away. But this instinct retained by
our chickens has become useless under domestication, for the mother-hen has
almost lost by disuse the power of flight.

Hence, we may conclude, that domestic instincts have been acquired and
natural instincts have been lost partly by habit, and partly by man
selecting and accumulating during successive generations, peculiar mental
habits and actions, which at first appeared from what we must in our
ignorance call an accident. In some cases compulsory habit alone has
sufficed to produce such inherited mental changes; in other cases
compulsory habit has done nothing, and all has been the result of
selection, pursued both methodically and unconsciously; but in most cases,
probably, habit and selection have acted together.

We shall, perhaps, best understand how instincts in a state of nature have
become modified by selection, by considering a few cases. I will select
only three, out of the several which I shall have to discuss in my future
work,--namely, the instinct which leads the cuckoo to lay her eggs i