By a continued process of this nature, I believe
that the strange instinct of our cuckoo could be, and has been,
generated. I may add that, according to Dr. Gray and to some other
observers, the European cuckoo has not utterly lost all maternal love
and care for her own offspring.
The occasional habit of birds laying their eggs in other birds' nests,
either of the same or of a distinct species, is not very uncommon with
the Gallinaceae; and this perhaps explains the origin of a singular
instinct in the allied group of ostriches. For several hen ostriches,
at least in the case of the American species, unite and lay first a
few eggs in one nest and then in another; and these are hatched by the
males. This instinct may probably be accounted for by the fact of the
hens laying a large number of eggs; but, as in the case of the cuckoo,
at intervals of two or three days. This instinct, however, of the
American ostrich has not as yet been perfected; for a surprising
number of eggs lie strewed over the plains, so that in one day's
hunting I picked up no less than twenty lost and wasted eggs.
Many bees are parasitic, and always lay their eggs in the nests of
bees of other kinds. This case is more remarkable than that of the
cuckoo; for these bees have not only their instincts but their
structure modified in accordance with their parasitic habits; for they
do not possess the pollen-collecting apparatus which would be
necessary if they had to store food for their own young.
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