The Descent of Man

number of the more complex instincts appear
to have been gained in a wholly different manner,
through the natural selection of variations
of simpler instinctive actions. Such variations
appear to arise from the same unknown causes
acting on the cerebral organisation, which induce
slight variations or individual differences
in other parts of the body; and these variations,
owing to our ignorance, are often said to arise
spontaneously. We can, I think, come to no
other conclusion with respect to the origin of
the more complex instincts, when we reflect on
the marvellous instincts of sterile worker- ants
and bees, which leave no offspring to inherit
the effects of experience and of modified habits.
Although, as we learn from the abovementioned
insects and the beaver, a high degree
of intelligence is certainly compatible with
complex instincts, and although actions, at first
learnt voluntarily can soon through habit be
performed with the quickness and certainty of