Darwin thinks it highly probable that the short feet of most breeds of
pigeons are due to lessened use, though he owns that the effects of
correlation with the shortened beak are more plainly shown than the
effects of disuse.[36] But why need the inherited effects of disuse be
called in to explain an average reduction of some 5 per cent., when
Darwin's measurements show that in the breeds where long beaks are
favoured the principle of correlation between these parts has lengthened
the foot by 13 per cent. in spite of disuse?