advanced as truly wonderful,
namely parents bringing food to their young which they themselves
neither like nor partake of{293};--for instance, the common sparrow, a
granivorous bird, feeding its young with caterpillars. We might of
course look into the case still earlier, and seek how an instinct in the
parent, of feeding its young at all, was first derived; but it is
useless to waste time in conjectures on a series of gradations from the
young feeding themselves and being slightly and occasionally assisted in
their search, to their entire food being brought to them. With respect
to the parent bringing a different kind of food from its own kind, we
may suppose either that the remote stock, whence the sparrow and other
congenerous birds have descended, was insectivorous, and that its own
habits and structure have been changed, whilst its ancient instincts
with respect to its young have remained unchanged; or we may suppose
that the parents have been induced to vary slightly the food of their
young, by a slight scarcity of the proper kind (or by the instincts of
some individuals not being so truly developed), and in this case those
young which were most capable of surviving were necessarily most often
preserved, and would themselves in time become parents, and would be
similarly compelled to alter their food for their young. In the case of
those animals, the young of which feed themselves, changes in their
instincts for food, and in their structure, might be selected from
slight variations, just as in mature animals. Again, where the food of
the young depends on where the mother places her eggs, as in the case of
the caterpillars of the cabbage-butterfly, we may suppose that the
parent stock of the species deposited her eggs sometimes on one kind and
sometimes on another of congenerous plants (as some species now do), and
if the cabbage suited the caterpillars better than any other plant, the
caterpillars of those butterflies, which had chosen the cabbage, would
be most plentifully reared, and would produce butterflies more apt to
lay their eggs on the cabbage than on the other congenerous plants.

{293} This is an expansion of an obscure passage in the Essay of
1842, p. 19.

However vague and unphilosophical these conjectures may appear, they
serve, I think, to show that one's first impulse utterly to reject any
theory whatever, implying a gradual acquirement of these instincts,
which for ages have excited m