A radiation of nerve-force of this kind,
if it caused a movement tending to lessen the primary irritation,
as in the case of the contraction of the iris preventing too much
light from falling on the retina, might afterwards have been
taken advantage of and modified for this special purpose.
It further deserves notice that reflex actions are in all probability
liable to slight variations, as are all corporeal structures and instincts;
and any variations which were beneficial and of sufficient importance,
would tend to be preserved and inherited. Thus reflex actions, when once
gained for one purpose, might afterwards be modified independently
of the will or habit, so as to serve for some distinct purpose.
Such cases would be parallel with those which, as we have every
reason to believe, have occurred with many instincts; for although
some instincts have been developed simply through long-continued
and inherited habit, other highly complex ones have been developed
through the preservation of variations of pre-existing instincts--
that is, through natural selection.
I have discussed at some little length, though as I am well aware,
in a very imperfect manner, the acquirement of reflex actions,
because they are often brought into play in connection with movements
expressive of our emotions; and it was necessary to show that at least
some of them might have been Erst acquired through the will in order
to satisfy a desire, or to relieve a disagreeable sensation.
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