On this view each group
would be returning to its ancestral home, led by the older birds,
in the great migration flights. The curious paths they follow are
believed by some authorities to mark the original lines of their
spread, preserved from generation to generation through the
annual lead of the older birds. If we recollect the Ice-Age which
drove the vast majority of the birds south at the end of the
Tertiary, and imagine them later following the northward retreat
of the ice, from their narrowed and overcrowded southern
territory, we may not be far from the secret of the annual
migration.
A more important controversy is conducted in regard to the
gorgeous plumage and other decorations and weapons of the male
birds. Darwin, as is known, advanced a theory of "sexual
selection" to explain these. The male peacock, to take a concrete
instance, would have developed its beautiful tail because,
through tens of thousands of generations, the female selected the
more finely tailed male among the various suitors. Dr. Wallace
and other authorities always disputed this aesthetic sentiment
and choice on the part of the female. The general opinion today
is that Darwin's theory could not be sustained in the range and
precise sense he gave to it.
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