They have shown, or they have tried to show (for I don't want
to dogmatise on the subject), how mind is gradually built up from the
simplest raw elements of sense and feeling; how emotions and intellect
slowly arise; how the action of the environment on the organism begets a
nervous system of ever greater and greater complexity, culminating at
last in the brain of a Newton, a Shakespeare, or a Mendelssohn. Step by
step, nerves have built themselves up out of the soft tissues as
channels of communication between part and part. Sense-organs of
extreme simplicity have first been formed on the outside of the body,
where it comes most into contact with external nature. Use and wont have
fashioned them through long ages into organs of taste and smell and
touch; pigment spots, sensitive to light or shade, have grown by
infinite gradations into the human eye or into the myriad facets of bee
and beetle; tremulous nerve-ends, responsive sympathetically to waves of
sound, have tuned themselves at last into a perfect gamut in the
developed ear of men and mammals. Meanwhile corresponding percipient
centres have grown up in the brain, so that the coloured picture flashed
by an external scene upon the eye is telegraphed from the sensitive
mirror of the retina, through the many-stranded cable of the optic
nerve, straight up to the appropriate headquarters in the thinking
brain. Stage by stage the continuous process has gone on unceasingly,
from the jelly-fish with its tiny black specks of eyes, through infinite
steps of progression, induced by ever-widening intercourse with the
outer world, to the final outcome in the senses and the emotions, the
intellect and the will, of civilised man.
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