behaviour that
may be anticipated,--signs which stimulate the appropriate attitude of
response. This would not, however, serve to account for the utility of
the organic accompaniments--heart-affection, respiratory changes,
vaso-motor effects and so forth, together with heightened muscular
tone,--on all of which Darwin lays stress[172] under his third
principle. The biological value of all this is, however, of great
importance, though Darwin was hardly in a position to take it fully
into account.

Having regard to the instinctive and hereditary factors of emotional
expression we may ask whether Darwin's third principle does not alone
suffice as an explanation. Whether we admit or reject Lamarckian
inheritance it would appear that all hereditary expression must be due
to pre-established connections within the central nervous system and
to a transmitted provision for coordinated response under the
appropriate stimulation. If this be so, Darwin's first and second
principles are subordinate and ancillary to the third, an expression,
so far as it is instinctive or heredity, being "the direct result of
the constitution of the nervous system."

Darwin accepted the emotions themselves as hereditary or acquired
states of mind and devoted his attention to their expression. But
these emotions themselves are genetic products and as such dependent
on organic conditions. It remained, therefore, for psychologists who
accepted evolution and sought to build on biological foundations to
trace the genesis of these modes of animal and human experience. The
subject has been independently developed by Professors Lange and
James;[173] and some modification of their view is regarded by many
evolutionists as affording the best explanation of the facts. We must
fix our attention on the lower emotions, such as anger or fear, and on
their first occurrence in the life of the individual organism. It is a
matter of observation that if a group of young birds which have been
hatched in an incubator are frightened by an appropriate presentation,
auditory or visual, they instinctively respond in special ways. If we
speak of this response as the expression, we find that there are many
factors. There are certain visible modes of behaviour, crouching at
once, scattering and then crouching, remaining motionless, the braced
muscles sustaining an attitude of arrest, and so forth, There are also
certain visceral or organic effects, such as affections of the h