The Descent of Man

y Mr. J. Jenner Weir that the bird-catchers can
distinguish the males by their slightly longer
beaks. The flocks of males are often found feeding
on the seeds of the teazle (Dipsacus),
which they can reach with their elongated
beaks, whilst the females more commonly feed
on the seeds of the betony or Scrophularia.
With a slight difference of this kind as a foundation,
we can see how the beaks of the two
sexes might be made to differ greatly through
natural selection. In some of the above cases,
however, it is possible that the beaks of the males
may have been first modified in relation to
their contests with other males; and that this
afterwards led to slightly changed habits of life.
LAW OF BATTLE.
Almost all male birds are extremely pugnacious,
using their beaks, wings, and legs for
fighting together. We see this every spring with
our robins and sparrows. The smallest of all