Any contrivance which shows an interdependence of parts, that results in
unity of action, is super-mechanical. The solar system may be regarded
as a unit, but it has not the purposive unity of a living body. It is
one only in the sense that its separate bodies are all made of one
stuff, and obey the same laws and move together in the same direction,
but a living body is a unit because all its parts are in the service of
one purposive end. An army is a unit, a flock of gregarious birds, a
colony of ants or bees, is a unit because the spirit and purpose of one
is the spirit and purpose of all; the unity is psychological.
Only living bodies are adaptive. Adaptation, of course, has its physics
or its chemistry, because it is a physical phenomenon; but there is no
adaptation of a rock or a clay-bank to its environment; there is only
mechanical and chemical adjustment. The influence of the environment may
bring about chemical and physical changes in a non-living body, but they
are not purposive as in a living body. The fat in the seeds of plants in
northern countries is liquid and solid at a lower temperature than in
tropical climates. Living organisms alone react in a formative or
deformative way to external stimuli. In warm climates the fur of
animals and the wool of sheep become thin and light. The colder the
climate, the thicker these coverings. Such facts only show that in the
matter of adaptation among living organisms, there is a factor at work
other than chemistry and physics--not independent of them, but making a
purposive use of them. Cut off the central shoot that leads the young
spruce tree upwards, and one of the shoots from the whirl of lateral
branches below it slowly rises up and takes the place of the lost
leader. Here is an action not prompted by the environment, but by the
morphological needs of the tree, and it illustrates how different is its
unity from the unity of a mere machine. I am only aiming to point out
that in all living things the material forces behave in a purposive way
to a degree that cannot be affirmed of them in non-living, and that,
therefore, they imply intelligence.
Evidently the cells in the body do not all have the same degree of
life,--that is, the same degree of irritability. The bone cells and the
hair cells, for instance, can hardly be so much alive--or so
irritable--as the muscle cells; nor these as intensely alive as the
nerve and brain cells. Does not a bird possess a higher degree of life
than a mollusk, or a turtle? Is not a brook trout more alive than a
mud-sucker? You can freeze the latter as stiff as an icicle and
resuscitate it, but not the former. There is a scale of degrees in life
as clearly as there is a scale of degrees in temperature. There is an
endless gradation of sensibilities of the living cells, dependent
probably upon the degree of differentiation of function. Anæsthetics
dull or suspend this irritability. The more highly developed and complex
the nervous system, the higher the degree of life, till we pass from
mere physical life to psychic life. Science might trace this difference
to cell structure, but what brings about the change in the character of
the cell, or starts the cells to building a complex nervous system, is a
question unanswerable to science. The biologist imagines this and that
about the invisible or hypothetical molecular structure; he assigns
different functions to the atoms; some are for endosmosis, others for
contraction, others for conduction of stimuli. Intramolecular oxygen
plays a part. Other names are given to the mystery--the micellar strings
of Naegeli, the biophores of Weismann, the plastidules of Haeckel; they
all presuppose millions of molecules peculiarly arranged in the
protoplasm.
On purely mechanical and chemical principles Tyndall accounts for the
growth from the germ of a tree. The germ would be quiet, but the solar
light and heat disturb its dreams, break up its atomic equilibrium. The
germ makes an "effort" to restore it (why does it make an effort?),
which effort is necessarily defeated and incessantly renewed, and in
the turmoil or "scrapping" between the germ and the solar forces, matter
is gathered from the soil and from the air and built into the special
form of a tree. Why not in the form of a cabbage, or a donkey, or a
clam? If the forces are purely automatic, why not? Why should matter be
gathered in at all in a mechanical struggle between inorganic elements?
But these are not all inorganic; the seed is organic. Ah! that makes the
difference! That accounts for the "effort." So we have to have the
organic to start with, then the rest is easy. No doubt the molecules of
the seed would remain in a quiescent state, if they were not disturbed
by external influences, chemical and mechanical. But there is something
latent or potential in that seed that is the opposite of the mechanical,
namely, the vital, and in what that consists, and where it came from, is
the mystery.