XIV 
FUNDAMENTAL FROBLEMS 
415 
reduction of those muscles. The amount of reduction observed 
by Darwin in the wing-bones of domestic ducks and poultry, 
and in the hind legs of tame rabbits, is very small, and is 
certainly no greater than the above causes will well account 
for; while so many of the external characters of all our 
domestic animals have been subject to long-continued artificial 
selection, and we are so ignorant of the possible correlations 
of different parts, that the phenomena presented by them 
seem sufficiently explained without recurrence to the assump¬ 
tion that any changes in the individual, due to disuse, are 
inherited by the offspring. 
Supposed Effects of Disuse among Wild Animals. 
It may be urged, however, that among wild animals we have 
many undoubted results of disuse much more pronounced than 
those among domestic kinds, results which cannot be explained 
by the causes already adduced. Such are the reduced size of 
the wings of many birds on oceanic islands ; the abortion of 
the eyes in many cave animals, and in some which live under¬ 
ground ; and the loss of the hind limbs in whales and in some 
lizards. These cases differ greatly in the amount of the re¬ 
duction of parts which has taken place, and may be due to 
different causes. It is remarkable that in some of the birds 
of oceanic islands the reduction is little if any greater than in 
domestic birds, as in the water-hen of Tristan d’Acunha. Now 
if the reduction of wing were due to the hereditary effects of 
disuse, we should expect a very much greater effect in a bird 
inhabiting an oceanic island than in a domestic bird, where the 
disuse has been in action for an indefinitely shorter period. 
In the case of many other birds, however—as some of the New 
Zealand rails and the extinct dodo of Mauritius—the wings 
have been reduced to a much more rudimentary condition, 
though it is still obvious that they were once organs of flight; 
and in these cases we certainly require some other causes than 
those which have reduced the wings of our domestic fowls. 
One such cause may have been of the same nature as that 
which has been so efficient in reducing the wings of the insects 
of oceanic islands—the destruction of those which, during the 
occasional use of their wings, were carried out to sea. This 
form of natural selection may well have acted in the case of 
