Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

THE PHILOSOPHY OF BIRDS' NESTS. 219
good, sometimes distinctly, sometimes more obscurely
apparent, according as the habits of the species are
more marked, or their structure more peculiar. It
is true that, among birds differing but little in structure or habits, we see considerable diversity in the
mode of nesting, but we are now so well assured that
important changes of climate and of surface have occured within the period of existing species, that it
is by no means difficult to see how such differences
have arisen. Simple habits are known to be hereditary, and as the area now occupied by each species
is different from that of every other, we may be sure
that such changes would act differently upon each, and
would often bring together species which had acquired
their peculiar habits in distinct regions and under
different conditions.
How do Young Birds learn to Build their First ANest?
But it is objected, birds do not learn to make their
nest as man does to build, for all birds will make
exactly the same nest as the rest of their species, even if
they have never seen one, and it is instinct alone that
can enable them to do this. No doubt this would be
instinct if it were true, and I simply ask for proof
of the fact. This point, although so important to the
question at issue, is always assumed without proof, and
even against proof, for what facts there are, are opposed to it. Birds brought up from the egg in cages
do not make the characteristic nest of their species,
even though the proper materials are supplied them,